Low-expansion-rate silicon-oxygen negative electrode material based on porous carbon carrier and preparation method of low-expansion-rate silicon-oxygen negative electrode material

Abstract

The invention relates to the technical field of silicon-oxygen negative electrode materials, in particular to a low-expansion-rate silicon-oxygen negative electrode material based on a porous carbon carrier and a preparation method thereof.The preparation method comprises the steps that 1, raw oil is pretreated to obtain a low-condensation-degree carbon-rich precursor; 2, sequentially carrying out oxidation crosslinking, molecular cutting, pre-oxidation and activation treatment on the low-condensation-degree carbon-rich precursor to obtain a porous carbon carrier; and step 3, taking the porous carbon carrier as a substrate, and carrying out vapor deposition and pyrolysis treatment to obtain the low-expansion-rate silicon-oxygen negative electrode material. According to the invention, the porous carbon carrier is used as the substrate, and the silicon-oxygen negative electrode material is obtained through vapor deposition and pyrolysis treatment, and has the characteristics of low expansion rate, good cycle stability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-oxygen negative electrode materials, and in particular to a low-expansion silicon-oxygen negative electrode material based on a porous carbon carrier and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles, portable electronic devices, and large-scale energy storage systems, lithium-ion batteries are facing higher demands for cycle performance, energy density, and safety. However, the currently widely used full-cell battery consisting of a graphite anode and nickel-cobalt-manganese oxide has an energy density of only 250 Wh / kg, which is difficult to meet these requirements. To achieve the goal of 400-500 Wh / kg, the development of high-energy-density electrode materials is crucial.

[0003] Among the many anode materials, silicon-based materials are of great significance for improving battery energy density due to their high specific capacity (4200 mAh / g) (10 times higher than that of graphite anodes). Adding 5-10 wt% silicon anode material to graphite can achieve a power battery energy density of 300 Wh / kg. Silicon also has a slightly higher lithium insertion potential than graphite, which can inhibit lithium dendrite growth and reduce safety risks. Silicon is also abundant and environmentally friendly. However, silicon undergoes a large volume change (300%-400%) during lithium insertion and delithiation, and issues such as the continuous growth of the SEI film, low intrinsic conductivity, and low lithium ion diffusion rate have hindered its commercial application.

[0004] Silicon dioxide (SiOx, 0≤x≤2) is considered one of the most promising anode materials for next-generation lithium-ion batteries due to its suitable operating potential and high theoretical capacity. However, it undergoes a certain volume expansion during the charge and discharge process, causing the material's capacity to decay rapidly, resulting in poor charge and discharge cycle performance.

[0005] Therefore, the present invention studies a low expansion rate silicon-oxygen negative electrode material based on a porous carbon carrier and a preparation method thereof. Summary of the Invention

[0006] In order to overcome the defects of the existing technology, the technical problem solved by the present invention is to provide a low-expansion silicon-oxygen negative electrode material based on a porous carbon carrier and a preparation method thereof. The present invention uses a porous carbon carrier as a substrate, and obtains a silicon-oxygen negative electrode material through vapor deposition and pyrolysis treatment. The material has the characteristics of low expansion rate and good cycle stability.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a low expansion rate silicon-oxygen negative electrode material based on a porous carbon carrier, comprising:

[0009] Step 1: Pre-treating the crude oil to obtain a low-condensation carbon-rich precursor;

[0010] Step 2: The low-condensation carbon-rich precursor is subjected to oxidative crosslinking, molecular cleavage, pre-oxidation, and activation treatments to obtain a porous carbon support;

[0011] Step three: using a porous carbon support as a substrate, vapor deposition and pyrolysis treatment are performed to obtain a low expansion rate silicon-oxygen negative electrode material.

[0012] In step 1, the feedstock oil is one or more of medium- and low-temperature coal tar, catalytic cracking slurry, ethylene tar, vacuum residue, and visbreaking residue; the low-condensation carbon-rich precursor has the following indicators: saturates ≤ 10 wt%, aromatics ≥ 60 wt%, colloids ≥ 18 wt%, asphaltenes ≤ 1 wt%, ash ≤ 0.05 wt%, H / C atomic ratio (0.1-0.15): 1, S ≥ 6 wt%, and N ≥ 7 wt%.

[0013] In the step 1, the pretreatment is one or more of solid-liquid separation, "solvent method" sedimentation, solvent extraction and refining, solvent deasphalting, furfural solvent refining, supercritical fluid extraction, catalytic hydrogenation, and short-process molecular cutting.

[0014] In the step 2, the crosslinking agent for the oxidative crosslinking treatment is one or more solvents selected from the group consisting of toluenesulfonic acid, paraformaldehyde, benzaldehyde alkylbenzenesulfonic acid, unsaturated fatty acid, and petroleum cyclopentane acid compounds, or a composite solvent of the above solvents. The mass ratio of the crosslinking agent to the low condensation degree carbon-rich precursor is (1-10):100, the vacuum degree is 0.01-0.09 MPa, the heating rate is 5-15°C / min, the reaction temperature is 280-420°C, and the treatment time is 0.5-4h.

[0015] In the step 2, according to the molecular weight requirement of the component to be removed from the oxidative cross-linking product, the molecular cutting is a single-stage or multi-stage treatment; the multi-stage treatment adopts a step-by-step treatment; the extractant used is any one of acetone, benzene, toluene, xylene, pyridine, quinoline, furfural, N-methylpyrrolidone, medium wash oil, and kerosene, or a mixture of two or more thereof, and the reaction conditions are: reaction temperature: 30-150° C., time: 0.5-8 h, vacuum degree: 0.01-0.09 MPa, screen mesh: 300-1200 mesh; 5000≤molecular weight<50000, adopting a single-stage molecular cutting; 2600≤molecular weight<5000, adopting a secondary molecular cutting; 200≤molecular weight<2600, adopting a third or higher level molecular cutting.

[0016] In the step 2, the pre-oxidation oxidant is one of HNO3, H2SO4, KMnO4, and H2O2, the oxidation reaction temperature is 150~350°C, the oxidation residence time is 1~6h, and the mass ratio of the oxidant to the molecular cleavage product is (0.5~2):1.

[0017] In the step 2, according to the requirements of the porous carbon support structure, the activation process is one or more activation treatments; the multi-stage activation treatment is carried out stage by stage; the first stage activation treatment is surface modification, and the reaction conditions are as follows: the reaction temperature is 500-800°C, the reaction atmosphere is oxygen or air or carbon dioxide, the flow rate is 60-300 L / h, and the reaction time is 0.5-15h; the second stage activation treatment is etching, and the reaction conditions are as follows: the reaction temperature is 600-1200°C, the reaction time is 2-10h, and the reaction medium is one of KOH, NaOH, CO2, water vapor, NaHCO3, KHCO3, and H3PO4; the conditions for the three-stage and above activation treatments adopt the second-stage activation treatment conditions;

[0018] 600m 2 / g≤Specific surface area of ​​porous carbon carrier<1000m 2 / g, when the proportion of micropores is ≥10% and the proportion of mesopores is ≥30%, one-stage activation treatment is adopted; 1000m 2 / g≤Specific surface area of ​​porous carbon carrier<1600m 2 / g, when the proportion of micropores is ≥20% and the proportion of mesopores is ≥40%, two-stage activation treatment is adopted; 1600m 2 / g≤Specific surface area of ​​porous carbon carrier<2200m 2 / g, when the proportion of micropores is ≥30% and the proportion of mesopores is ≥50%, more than three stages of activation treatment are used.

[0019] In the step 3, the silicon source gas for vapor deposition is monosilane (SiH4), disilane (Si2H6), silicon hydride (Si n H 2n+2 ), the gas flow rate is 2~30L / h, the carrier gas is Ar or N2, the gas flow rate is 10~60L / h, the oxygen concentration is less than 0.5ppm, the vacuum degree is 0.01~0.09Mpa, the reaction temperature is 600~1400℃, the heating rate is 2~15℃ / min, and the constant temperature time is 0.5~8h.

[0020] In step three, the pyrolysis reaction conditions are as follows: the carbon encapsulating agent is one or more of citric acid, glucose, sucrose, phenolic resin, polyvinyl chloride, polyacrylic acid, and polyvinyl alcohol; under nitrogen protection, the reaction temperature is 600-1200° C., the reaction time is 1-8 hours, and the mass ratio of the carbon encapsulating agent to the vapor deposition product is (0.2-4):1.

[0021] A method for preparing a low-expansion silicon-oxygen negative electrode material based on a porous carbon support. The prepared low-expansion silicon-oxygen negative electrode material has a three-layer structure, wherein the inner layer is a porous carbon support, the middle layer is a SiOx deposition phase, and the outer layer is a pyrolytic carbon coating layer; the porous carbon support has a specific surface area of ​​800~2000m 2 / g, micropores account for 10~30%, mesopores account for 30~50%, carbon content ≥90%; SiOx deposition phase, wherein SiOx content ≥60wt%; pyrolytic carbon coating layer, which is an amorphous structure, carbon content ≥92%, graphitization degree ≤70%; the particle size distribution of silicon oxide negative electrode material is D 10 :6~12μm、D 50 :15~24μm、D 90 : 28~45μm, true density ≥2.24g / cm 3 , tap density ≥0.9g / cm 3 , the powder compaction density is ≥1.55g / cm 3 , ash content ≤ 0.01%, specific surface area ≤ 1.8m 2 / g, interlayer spacing (d 002 ) is 0.34nm~0.375nm, and the thickness of the carbon layer is 5~20nm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention uses a porous carbon carrier as a substrate, and after vapor deposition and pyrolysis treatment, the obtained silicon-oxygen negative electrode material has good gram-specific capacity, rate performance and cycle stability, meeting the demand for high gram-specific capacity and low expansion rate silicon-oxygen negative electrode materials for lithium-ion batteries.

[0024] 2) This invention prepares a carbon support with a three-dimensional porous network structure through processes including feedstock pretreatment, oxidative crosslinking, molecular cleavage, pre-oxidation, and activation. This support, composed of interconnected amorphous carbon, exhibits a high specific surface area, a controllable thermal expansion coefficient, excellent thermal conductivity, and low density. Its continuous three-dimensional pore structure provides an ideal buffer space for the silicon-oxygen anode material, significantly suppressing the volume expansion effect during charge and discharge, thereby significantly improving the battery's cycling stability.

[0025] 3) The carbon coating layer formed by pyrolysis treatment in the present invention forms a conductive network, which improves the conductivity and structural stability of the material, promotes the rapid transmission of lithium ions, and improves the rate performance.

[0026] 4) The method for preparing a low expansion rate silicon-oxygen negative electrode material provided by the present invention is simple, the process flow is easy to control, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 This is the charge and discharge curve of the low expansion rate silicon oxide negative electrode material of the present invention.

[0029] Figure 2 This is the cycle curve of the low expansion rate silicon oxide negative electrode material of the present invention. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are further described below:

[0031] The present invention provides a method for preparing a low expansion rate silicon-oxygen negative electrode material based on a porous carbon carrier, comprising:

[0032] Step 1: Pre-treating the crude oil to obtain a low-condensation carbon-rich precursor;

[0033] Step 2: The low-condensation carbon-rich precursor is subjected to oxidative crosslinking, molecular cleavage, pre-oxidation, and activation treatments to obtain a porous carbon support;

[0034] Step three: using a porous carbon support as a substrate, vapor deposition and pyrolysis treatment are performed to obtain a low expansion rate silicon-oxygen negative electrode material.

[0035] In step 1, the feedstock oil is one or more of medium- and low-temperature coal tar, catalytic cracking slurry, ethylene tar, vacuum residue, and visbreaking residue; the low-condensation carbon-rich precursor has the following indicators: saturates ≤ 10 wt%, aromatics ≥ 60 wt%, colloids ≥ 18 wt%, asphaltenes ≤ 1 wt%, ash ≤ 0.05 wt%, H / C atomic ratio (0.1-0.15): 1, S ≥ 6 wt%, and N ≥ 7 wt%.

[0036] In the step 1, the pretreatment is one or more of solid-liquid separation, "solvent method" sedimentation, solvent extraction and refining, solvent deasphalting, furfural solvent refining, supercritical fluid extraction, catalytic hydrogenation, and short-process molecular cutting.

[0037] In the step 2, the crosslinking agent for the oxidative crosslinking treatment is one or more solvents selected from the group consisting of toluenesulfonic acid, paraformaldehyde, benzaldehyde alkylbenzenesulfonic acid, unsaturated fatty acid, and petroleum cyclopentane acid compounds, or a composite solvent of the above solvents. The mass ratio of the crosslinking agent to the low condensation degree carbon-rich precursor is (1-10):100, the vacuum degree is 0.01-0.09 MPa, the heating rate is 5-15°C / min, the reaction temperature is 280-420°C, and the treatment time is 0.5-4h.

[0038] In step 2, molecular cutting is performed in one or multiple stages according to the molecular weight requirement of the component to be removed from the oxidative cross-linking product; the multi-stage treatment adopts step-by-step treatment; the extractant used is any one of acetone, benzene, toluene, xylene, pyridine, quinoline, furfural, N-methylpyrrolidone, medium wash oil, kerosene, or a mixture of two or more thereof; the reaction conditions are: reaction temperature: 30-150°C, reaction time: 0.5-8h, vacuum degree: 0.01-0.09MPa, screen mesh: 300-1200 mesh; for molecular weights of 5000≤<50000, a first-stage molecular cutting is used; for molecular weights of 2600≤<5000, a second-stage molecular cutting is used; for molecular weights of 200≤<2600, a third-stage or higher molecular cutting is used. When a third-stage molecular cutting is used, the first-stage treatment is performed first, followed by the second-stage treatment, and finally the third-stage treatment.

[0039] In the step 2, the pre-oxidation oxidant is one of HNO3, H2SO4, KMnO4, and H2O2, the oxidation reaction temperature is 150~350°C, the oxidation residence time is 1~6h, and the mass ratio of the oxidant to the molecular cleavage product is (0.5~2):1.

[0040] In the step 2, according to the requirements of the porous carbon support structure, the activation process is one or more activation treatments; the multi-stage activation treatment is carried out stage by stage; the first stage activation treatment is surface modification, and the reaction conditions are as follows: the reaction temperature is 500-800°C, the reaction atmosphere is oxygen or air or carbon dioxide, the flow rate is 60-300 L / h, and the reaction time is 0.5-15h; the second stage activation treatment is etching, and the reaction conditions are as follows: the reaction temperature is 600-1200°C, the reaction time is 2-10h, and the reaction medium is one of KOH, NaOH, CO2, water vapor, NaHCO3, KHCO3, and H3PO4; the conditions for the three-stage and above activation treatments adopt the second-stage activation treatment conditions;

[0041] 600m 2 / g≤Specific surface area of ​​porous carbon carrier<1000m 2 / g, when the proportion of micropores is ≥10% and the proportion of mesopores is ≥30%, one-stage activation treatment is adopted; 1000m 2 / g≤Specific surface area of ​​porous carbon carrier<1600m 2 / g, when the proportion of micropores is ≥20% and the proportion of mesopores is ≥40%, two-stage activation treatment is adopted; 1600m 2 / g≤Specific surface area of ​​porous carbon carrier<2200m 2 / g, when the micropore ratio is ≥30% and the mesopore ratio is ≥50%, three or more stages of activation treatment are used. When three-stage activation treatment is used, the first stage is carried out first, followed by the second stage, and finally the third stage.

[0042] In the step 3, the silicon source gas for vapor deposition is monosilane (SiH4), disilane (Si2H6), silicon hydride (Si n H 2n+2 ), the gas flow rate is 2~30L / h, the carrier gas is Ar or N2, the gas flow rate is 10~60L / h, the oxygen concentration is less than 0.5ppm, the vacuum degree is 0.01~0.09Mpa, the reaction temperature is 600~1400℃, the heating rate is 2~15℃ / min, and the constant temperature time is 0.5~8h.

[0043] In step three, the pyrolysis reaction conditions are as follows: the carbon encapsulating agent is one or more of citric acid, glucose, sucrose, phenolic resin, polyvinyl chloride, polyacrylic acid, and polyvinyl alcohol; under nitrogen protection, the reaction temperature is 600-1200° C., the reaction time is 1-8 hours, and the mass ratio of the carbon encapsulating agent to the vapor deposition product is (0.2-4):1.

[0044] A method for preparing a low-expansion silicon-oxygen negative electrode material based on a porous carbon support. The prepared low-expansion silicon-oxygen negative electrode material has a three-layer structure, wherein the inner layer is a porous carbon support, the middle layer is a SiOx deposition phase, and the outer layer is a pyrolytic carbon coating layer; the porous carbon support has a specific surface area of ​​800~2000m 2 / g, micropores account for 10~30%, mesopores account for 30~50%, carbon content ≥90%; SiOx deposition phase, wherein SiOx content ≥60wt%; pyrolytic carbon coating layer, which is an amorphous structure, carbon content ≥92%, graphitization degree ≤70%; the particle size distribution of silicon oxide negative electrode material is D 10 :6~12μm、D 50 :15~24μm、D 90 : 28~45μm, true density ≥2.24g / cm 3 , tap density ≥0.9g / cm 3 , the powder compaction density is ≥1.55g / cm 3 , ash content ≤ 0.01%, specific surface area ≤ 1.8m 2 / g, interlayer spacing (d 002 ) is 0.34nm~0.375nm, and the thickness of the carbon layer is 5~20nm.

[0045] Example:

[0046] Table 1 shows the process parameters for preparing low expansion silicon-oxygen negative electrode materials in various examples. Table 2 shows the performance indicators of low expansion silicon-oxygen negative electrode materials prepared in various examples.

[0047] Table 1 Preparation process parameters of low expansion rate silicon oxide negative electrode materials

[0048]

[0049]

[0050] Table 2 shows the performance indicators of the low expansion rate silicon oxide negative electrode materials prepared in each embodiment

[0051]

[0052] It can be seen from this that, combined with Figure 1 and Figure 2 It can be seen that the low-expansion silicon-oxygen negative electrode material based on a porous carbon carrier and the preparation method thereof provided by the present invention has the advantages of a low-expansion silicon-oxygen negative electrode material having an initial coulombic efficiency ≥90%, an initial discharge specific capacity ≥450 mAh / g, a capacity retention rate of ≥80% after 400 0.5C cycles, a cycle performance ≥800 cycles, and a rate performance (2C / 0.2C) ≥80%. It has the advantages of small expansion rate, long safe use period, and good cycle stability.

[0053] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, and these simple modifications all fall within the scope of protection of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. In order to avoid unnecessary repetition, the present invention will no longer describe various possible combinations separately. In addition, the various different embodiments of the present invention can also be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a low expansion rate silicon-oxygen negative electrode material based on a porous carbon support, characterized in that: The steps include: Step 1: Pre-treating the crude oil to obtain a low-condensation carbon-rich precursor; Step 2: The low-condensation carbon-rich precursor is subjected to oxidative crosslinking, molecular cleavage, pre-oxidation, and activation treatment to obtain a porous carbon support; Step 3: Using a porous carbon support as a substrate, vapor deposition and pyrolysis treatment are performed to obtain a low expansion rate silicon-oxygen negative electrode material; In step 1, the feedstock oil is one or more selected from the group consisting of medium- and low-temperature coal tar, catalytic cracking slurry, ethylene tar, vacuum residue, and visbreaking residue; the low-condensation carbon-rich precursor has the following indicators: saturates ≤ 10 wt%, aromatics ≥ 60 wt%, colloids ≥ 18 wt%, asphaltenes ≤ 1 wt%, ash ≤ 0.05 wt%, H / C atomic ratio (0.1-0.15): 1, S ≥ 6 wt%, and N ≥ 7 wt%; In the step 1, the pretreatment is one or more of solid-liquid separation, "solvent method" sedimentation, solvent extraction and refining, solvent deasphalting, furfural solvent refining, supercritical fluid extraction, catalytic hydrogenation, and short-process molecular cutting.

2. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In the step 2, the crosslinking agent for the oxidative crosslinking treatment is one or more solvents selected from the group consisting of toluenesulfonic acid, paraformaldehyde, benzaldehyde alkylbenzenesulfonic acid, unsaturated fatty acid, and petroleum cyclopentane acid compounds, or a composite solvent of the above solvents. The mass ratio of the crosslinking agent to the low condensation degree carbon-rich precursor is (1-10):100, the vacuum degree is 0.01-0.09 MPa, the heating rate is 5-15°C / min, the reaction temperature is 280-420°C, and the treatment time is 0.5-4h.

3. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In the step 2, according to the molecular weight requirement of the component to be removed from the oxidative cross-linking product, the molecular cutting is a single-stage or multi-stage treatment; the multi-stage treatment adopts a step-by-step treatment; the extractant used is any one of acetone, benzene, toluene, xylene, pyridine, quinoline, furfural, N-methylpyrrolidone, medium wash oil, and kerosene, or a mixture of two or more thereof, and the reaction conditions are: reaction temperature: 30-150° C., time: 0.5-8 h, vacuum degree: 0.01-0.09 MPa, screen mesh: 300-1200 mesh; 5000≤molecular weight<50000, adopting a single-stage molecular cutting; 2600≤molecular weight<5000, adopting a secondary molecular cutting; 200≤molecular weight<2600, adopting a third or higher level molecular cutting.

4. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In the step 2, the pre-oxidation oxidant is one of HNO3, H2SO4, KMnO4, and H2O2, the oxidation reaction temperature is 150~350°C, the oxidation residence time is 1~6h, and the mass ratio of the oxidant to the molecular cleavage product is (0.5~2):

1.

5. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In the step 2, according to the requirements of the porous carbon support structure, the activation process is one or more activation treatments; the multi-stage activation treatment is carried out stage by stage; the first stage activation treatment is surface modification, and the reaction conditions are as follows: the reaction temperature is 500-800°C, the reaction atmosphere is oxygen or air or carbon dioxide, the flow rate is 60-300 L / h, and the reaction time is 0.5-15h; the second stage activation treatment is etching, and the reaction conditions are as follows: the reaction temperature is 600-1200°C, the reaction time is 2-10h, and the reaction medium is one of KOH, NaOH, CO2, water vapor, NaHCO3, KHCO3, and H3PO4; the conditions for the three-stage and above activation treatments adopt the second-stage activation treatment conditions; 600m 2 / g≤Specific surface area of ​​porous carbon carrier<1000m 2 / g, when the proportion of micropores is ≥10% and the proportion of mesopores is ≥30%, one-stage activation treatment is adopted; 1000m 2 / g≤Specific surface area of ​​porous carbon carrier<1600m 2 / g, when the proportion of micropores is ≥20% and the proportion of mesopores is ≥40%, two-stage activation treatment is adopted; 1600m 2 / g≤Specific surface area of ​​porous carbon carrier<2200m 2 / g, when the proportion of micropores is ≥30% and the proportion of mesopores is ≥50%, more than three stages of activation treatment are used.

6. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In the step 3, the silicon source gas for vapor deposition is monosilane (SiH4), disilane (Si2H6), silicon hydride (Si n H 2n+2 ), the gas flow rate is 2~30L / h, the carrier gas is Ar or N2, the gas flow rate is 10~60L / h, the oxygen concentration is less than 0.5ppm, the vacuum degree is 0.01~0.09Mpa, the reaction temperature is 600~1400℃, the heating rate is 2~15℃ / min, and the constant temperature time is 0.5~8h.

7. The method for preparing a low expansion coefficient silicon-oxygen negative electrode material based on a porous carbon support according to claim 1, characterized in that: In step three, the pyrolysis reaction conditions are as follows: the carbon encapsulating agent is one or more of citric acid, glucose, sucrose, phenolic resin, polyvinyl chloride, polyacrylic acid, and polyvinyl alcohol; under nitrogen protection, the reaction temperature is 600-1200° C., the reaction time is 1-8 hours, and the mass ratio of the carbon encapsulating agent to the vapor deposition product is (0.2-4):

1.

8. The low expansion rate silicon-oxygen negative electrode material prepared by the method for preparing a low expansion rate silicon-oxygen negative electrode material based on a porous carbon support according to any one of claims 1 to 7, characterized in that: The low expansion rate silicon oxide negative electrode material has a three-layer structure, the inner layer is a porous carbon support, the middle layer is a SiOx deposition phase, and the outer layer is a pyrolytic carbon coating layer; the porous carbon support has a specific surface area of ​​800~2000m 2 / g, micropores account for 10~30%, mesopores account for 30~50%, carbon content ≥90%; SiOx deposition phase, wherein SiOx content ≥60wt%; pyrolytic carbon coating layer, which is an amorphous structure, carbon content ≥92%, graphitization degree ≤70%; the particle size distribution of silicon oxide negative electrode material is D 10 :6~12μm、D 50 :15~24μm、D 90 : 28~45μm, true density ≥2.24g / cm 3 , tap density ≥0.9g / cm 3 , the powder compaction density is ≥1.55g / cm 3 , ash content ≤ 0.01%, specific surface area ≤ 1.8m 2 / g, the interlayer spacing (d002) is 0.34nm~0.375nm, and the thickness of the carbon layer is 5~20nm.

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