Preparation of low expansion ratio silicon-carbon anode materials based on porous carbon framework and method

Abstract

This invention belongs to the technical field of silicon-carbon anode materials, and particularly relates to a method for preparing a low-expansion-rate silicon-carbon anode material based on a porous carbon framework. The method includes the following steps: 1) obtaining centrifugal liquid and centrifugal residue by supercentrifugation of raw oil; 2) obtaining heavy distillate oil by distillation of the centrifugal liquid, mixing it with a catalytic crosslinking agent, and then sequentially undergoing thermal polymerization, flash evaporation, and short-path molecular distillation to obtain a coating agent; 3) obtaining a porous carbon framework by sequentially undergoing pressure filtration, oxidative stabilization, surface modification, and carbonization of the centrifugal residue obtained in step 1); 4) uniformly mixing the porous carbon framework with silicon powder, adding the coating agent obtained in step 2), and then performing solid-phase coating and carbonization to obtain a low-expansion-rate silicon-carbon anode material. The advantages are: this low-expansion-rate silicon-carbon anode material has high capacity, long cycle life, excellent rate performance, and high initial coulombic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon anode material technology, and particularly relates to a method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework. Background Technology

[0002] With the widespread application and rapid development of various portable electronic products and electric vehicles, the demand for and performance requirements of chemical energy are constantly increasing. Lithium-ion batteries are a current research hotspot in the field of new energy due to their excellent performance, such as high specific energy, low self-discharge, high operating voltage, no memory effect, and green environmental protection. Currently, the main anode materials for lithium-ion batteries used in commercial production are carbon materials with low and stable operating potential and good cycle performance. However, the specific capacity of carbon materials is relatively low, and the lithium storage capacity of lithium-ion battery anode materials is a key factor restricting their application range. Silicon has a large theoretical specific capacity (4200mAh / g), which is an order of magnitude higher than that of graphite anode materials (372mAh / g) and has a lower lithium intercalation potential. Silicon has low reactivity with electrolyte, is abundant in the earth's crust, and is inexpensive, making it an ideal choice for the next generation of lithium-ion battery anode materials.

[0003] Silicon-carbon composites are a type of silicon-based composite material that has attracted increasing attention from researchers due to their unique advantages and potential. Silicon and carbon have similar chemical properties, and carbon-based anode materials exhibit small volume changes during charge and discharge, as well as good cycle stability and conductivity. Therefore, carbon-based materials are often chosen as the preferred matrix for composites with silicon. In order to further improve the electrochemical performance of silicon-carbon composites as anode materials for lithium-ion batteries, such as cycle stability and reversible cycle capacity retention, and to obtain alternatives to graphite as a new generation of lithium-ion battery anode materials, researchers have conducted extensive exploratory research in recent years and achieved significant results. Continuing to develop high-performance silicon-carbon composite materials is of great significance for their application in practical production.

[0004] In the prior art, patent publication number CN115986075A discloses a low-expansion silicon-carbon anode material and its preparation method for lithium-ion batteries. The material includes silicon-carbon particles, which comprise composite particles of porous materials and nanoscale silicon-based materials, a carbon coating layer, graphite, and organic pyrolysis carbon. The structure of the composite particles of porous materials and nanoscale silicon-based materials involves depositing a silicon layer of nanoscale silicon-based material within the pores of the porous material. This technical solution employs a vapor deposition method, which has a long process chain and high cost. Furthermore, silicon deposition depends on the pore size distribution of the porous material; uneven pore size can lead to uneven silicon dispersion. The carbon coating layer, formed through pyrolysis deposition, may not provide complete coverage. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing low expansion rate silicon-carbon anode materials based on a porous carbon framework. The prepared low expansion rate silicon-carbon anode materials have high capacity, long cycle life, excellent rate performance and high initial coulombic efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing low expansion rate silicon-carbon anode materials based on porous carbon framework includes the following steps:

[0008] 1) The raw oil is processed by super centrifugation to obtain centrifugal liquid and centrifugal residue;

[0009] 2) The centrifuged liquid is separated by distillation to obtain heavy distillate oil, which is then mixed with a catalytic crosslinking agent and subjected to thermal polymerization, flash evaporation, and short-path molecular distillation to obtain a coating agent;

[0010] 3) The centrifugal residue obtained in step 1) is subjected to pressure filtration, oxidation stabilization, surface modification and carbonization treatment in sequence to obtain a porous carbon skeleton;

[0011] 4) After the porous carbon skeleton and silicon powder are mixed evenly, the coating agent obtained in step 2) is added, and the mixture is subjected to solid-phase coating and carbonization treatment to obtain a silicon-carbon anode material with low expansion rate.

[0012] The feedstock oil has the following specifications: ash content < 0.05%, moisture content < 1.0%, and quinoline insoluble content ≥ 15%. The quinoline insoluble content includes primary organic quinoline insolubles and secondary quinoline insolubles, wherein the primary organic quinoline insoluble content is ≥ 10%, ash content < 0.05%, and particle size distribution is D. 50 : 0.5~1μm, D max : 1.5~2μm; secondary quinoline insoluble content ≥5%, ash content <0.05%, particle size distribution is D 50 5~30μm, D max : 40~50μm;

[0013] The feedstock oil is one or more of the following: poor and rich coal dry distillation tar, medium and low temperature coal tar, high temperature coal tar, catalytic cracking slurry oil, and ethylene residue oil.

[0014] The reaction conditions for the supercentrifugation treatment in step 1) are: separation temperature 30~80℃, separation time 0.5~5h, centrifugation speed 5000~20000rad / min, and sieve mesh 100~800 mesh.

[0015] The toluene-insoluble matter content in the centrifuged residue obtained in step 1) is ≥80%, and the ash content is <0.05%.

[0016] The reaction conditions for the distillation separation process in step 2) are as follows: top temperature of 160~280℃, bottom temperature of 320~400℃, vacuum degree of 0.01~0.09MPa, and recycle ratio of 0.6~1.2.

[0017] In step 2), the heavy distillate oil distilled at 380°C has a volume percentage ≥ 50%, a heptane-insoluble component mass percentage ≥ 70%, a toluene-soluble component mass percentage ≥ 50%, and a toluene-insoluble component mass percentage ≥ 5%.

[0018] In step 2), the catalytic crosslinking agent is one or more solvents selected from paraformaldehyde, benzaldehyde, glyoxal, glutaraldehyde, and alkylphenol resin, or a compound solvent of the solvents mentioned above.

[0019] The mass ratio of the catalytic crosslinking agent to the heavy distillate oil is (1~10):20.

[0020] The reaction conditions for thermal polymerization in step 2) are: heating rate of 5~15℃ / min, reaction temperature of 280~420℃, and treatment time of 1~8h;

[0021] In step 2), the flash evaporation is a multi-stage dynamic pressure-controlled flash evaporation. The reaction conditions for each stage of flash evaporation are as follows: the temperature of the radiant section of the heating furnace is 140~420℃, the temperature of the bottom of the flash evaporator is 120~400℃, the absolute pressure is 5~20kPa, and the residence time is 0.5~2h.

[0022] In the aforementioned short-path molecular distillation, the polymeric asphalt is at a temperature of 300–450°C and an absolute pressure of 0.5–30 kPa in the thin-film evaporator or short-path evaporator, and the residence time of the polymeric asphalt in the thin-film evaporator or short-path evaporator is 0.5–10 min.

[0023] The coating agent obtained in step 2) has a softening point of 180~280℃, a TI content of 40%~75%, a QI content of 0.01%~0.5%, an ash content of 0.01%~0.05%, and a CV content of 75%~85%.

[0024] In step 3), the pressure filtration process is performed once, twice, or more than three times depending on the molecular weight requirements of the filtration product.

[0025] If the molecular weight of the filter press product is 5000~50000, a single filter press is used; if the molecular weight of the filter press product is 2600~5000 (excluding 5000), a double filter press is used; if the molecular weight of the filter press product is 200~2600 (excluding 2600), a triple or higher filter press is used.

[0026] When the filtration process is performed twice, the first filtration process is performed first, followed by the second filtration process. When the filtration process is performed three or more times, the first filtration process is performed first, followed by the second filtration process. For filtration processes with three or more times, the process conditions of either the first or second filtration process are adopted.

[0027] The reaction conditions for the primary pressure filtration process are: extraction temperature 100~180℃, extraction time 1~8h, and sieve to obtain filter residue of 100~400 mesh; the mass ratio of primary extractant to centrifuged residue is (1~5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline;

[0028] The reaction conditions for the secondary pressure filtration process are: extraction temperature 40~80℃, extraction time 1~4h, and 200~800 mesh filter residue obtained by sieving. The mass ratio of the secondary extractant to the primary filter residue is (0.2~2):1. The secondary extractant is one or more of acetone, benzene, toluene, and xylene.

[0029] The reaction conditions for oxidation stabilization in step 3) are: reaction temperature of 260~380℃ and air flow rate of 1~10m³ / h. 3 / h, processing time 1~8h;

[0030] The surface modification is divided into one-stage or two-stage modification reaction processes, depending on the structural requirements of the surface modification product.

[0031] The surface-modified product structure requires a specific surface area of ​​600~1000 m². 2 / g, excluding 1000m 2 / g, when the micropore ratio is ≥10% and the mesopore ratio is ≥30%, a one-stage modification reaction treatment is adopted;

[0032] The specific surface area of ​​the surface-modified product structure is 1000~1800 m². 2 / g, excluding 1800m 2 When the micropore content is ≥20% and the mesopore content is ≥40%, a two-stage modification reaction treatment is adopted.

[0033] The specific surface area of ​​the surface-modified product structure is 1800~2800 m². 2 When the micropore content is ≥30% and the mesopore content is ≥50%, a modification reaction of three or more stages shall be adopted.

[0034] The reaction conditions are as follows: reaction temperature is 300~1200℃, reaction time is 0.5~10h; the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

[0035] The reaction conditions for the carbonization treatment are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 700~1800℃, and the final temperature holding time is 1~12h.

[0036] The porous carbon framework obtained in step 3) has the following properties: specific surface area of ​​800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, mesoporous content ≥30%.

[0037] The particle size distribution of the silicon powder in step 4) is: D 50 5~25nm, D max ≤180nm; The mass ratio of the silicon powder to the porous carbon skeleton is (1~5):20;

[0038] The mixing process is carried out using a VC mixer with a mixing speed of 400~1200 rad / min, a mixing time of 1~12 h, and a vacuum degree of 0.01~0.09 MPa.

[0039] The reaction conditions for solid-phase coating are as follows: coating temperature is 380~760℃, heating rate is 5~10℃ / min, isothermal time is 2~8h, stirring speed is 400~1200rad / min, vacuum degree is 0.01~0.09MPa; the agent-carbon ratio is the mass ratio of the coating agent to the mixture of porous carbon skeleton and silicon powder, which is (1~4):10.

[0040] The reaction conditions for the carbonization treatment are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 1400~1800℃, and the final temperature holding time is 2~8h.

[0041] A low expansion rate silicon-carbon anode material based on a porous carbon framework is disclosed. The low expansion rate silicon-carbon anode material has an initial discharge specific capacity ≥450mAh / g, an initial coulombic efficiency ≥88%, a capacity retention rate ≥82% after 400 0.2C cycles, a cycle performance ≥1000 cycles, a rate performance of 2C / 0.5C ≥80%, and a volume expansion rate ≤180%.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] The low-expansion-rate silicon-carbon anode material prepared by this invention exhibits high capacity, long cycle life, excellent rate performance, and high initial coulombic efficiency. The porous carbon framework provided during the preparation process has a high specific surface area and a reasonable pore distribution, which can buffer the stress changes caused by the volume expansion of silicon powder and provide expansion space during the silicon powder-carbon composite process, maintaining the integrity of the electrode structure. The uniform coating of the carbon layer not only reduces the specific surface area of ​​the silicon-carbon anode material but also increases the lithium-ion transport channels, further improving the electrochemical performance such as safe service life and rate performance. This invention also co-produces a lithium-ion battery anode material coating agent, possessing significant technical advantages and market application potential. Specific advantages include:

[0044] 1) The low expansion rate silicon-carbon anode material prepared by this invention has an initial discharge specific capacity ≥450mAh / g, an initial coulombic efficiency ≥88%, a capacity retention rate ≥82% after 400 0.2C cycles, and an expansion rate ≤180%.

[0045] 2) The solid-phase mixing and co-production coating technology of this invention can form a uniform carbon layer, which not only reduces the specific surface area of ​​the silicon-carbon anode material, but also increases the lithium-ion transport channels, further improving the electrochemical performance such as safe service life and rate capability. Cycle performance ≥1000 cycles, rate performance (2C / 0.2C) ≥80%.

[0046] 3) The porous carbon framework provided by this invention has a high specific surface area and a reasonable pore distribution, which can buffer the stress changes caused by the volume expansion of silicon powder, provide expansion space during the silicon powder-to-carbon composite process, and maintain the integrity of the electrode structure. The specific surface area is 800~2000 m² / g. 2 / g, pore volume 0.4~1.4cm 3 / g, mesoporous content ≥30%. Attached Figure Description

[0047] Figure 1 This is a charge-discharge curve of a low-expansion-rate silicon-carbon anode material prepared based on a porous carbon framework.

[0048] Figure 2 This is a cycle curve diagram of a low expansion rate silicon-carbon anode material prepared based on a porous carbon framework. Detailed Implementation

[0049] The present invention will now be described in detail, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0050] A method for preparing low expansion rate silicon-carbon anode materials based on porous carbon framework includes the following steps:

[0051] 1) The raw oil is processed by super centrifugation to obtain centrifugal liquid and centrifugal residue;

[0052] The specifications for the feedstock oil are: ash content < 0.05%, moisture content < 1.0%, and quinoline insoluble content ≥ 15%. The quinoline insoluble content in the feedstock oil includes primary organic quinoline insolubles and secondary quinoline insolubles, of which the content of primary organic quinoline insolubles is ≥ 10%, ash content < 0.05%, and particle size distribution is D. 50 : 0.5~1μm, D max : 1.5~2μm; secondary quinoline insoluble content ≥5%, ash content <0.05%, particle size distribution is D 50 5~30μm, D max 40~50μm. The feedstock is one or more of the following: lean and rich coal dry distillation tar, medium and low temperature coal tar, high temperature coal tar, catalytic cracking slurry oil, and ethylene residue oil.

[0053] The reaction conditions for supercentrifugation are: separation temperature 30~80℃, separation time 0.5~5h, centrifugation speed 5000~20000rad / min, and sieve mesh 100~800 mesh.

[0054] The obtained centrifuged residue contains ≥80% toluene-insoluble matter and <0.05% ash.

[0055] 2) The centrifuged liquid is separated by distillation to obtain heavy distillate oil, which is then mixed with a catalytic crosslinking agent and subjected to thermal polymerization, flash evaporation, and short-path molecular distillation to obtain a coating agent.

[0056] The reaction conditions for distillation separation are: top temperature of 160~280℃, bottom temperature of 320~400℃, vacuum degree of 0.01~0.09MPa, and recycle ratio of 0.6~1.2.

[0057] The volume percentage of the heavy distillate oil distilled at 380℃ is ≥50%, the mass percentage of heptane-insoluble components is ≥70%, the mass percentage of toluene-soluble components is ≥50%, and the mass percentage of toluene-insoluble components is ≥5%.

[0058] The catalytic crosslinking agent is one or more solvents selected from paraformaldehyde, benzaldehyde, glyoxal, glutaraldehyde, and alkylphenol resin, or a compound solvent of the solvents mentioned above; the mass ratio of the catalytic crosslinking agent to the heavy distillate oil is (1~10):20.

[0059] The reaction conditions for thermal polymerization are: heating rate of 5~15℃ / min, reaction temperature of 280~420℃, and treatment time of 1~8h.

[0060] Flash evaporation is a multi-stage dynamic pressure controlled flash evaporation process, employing a multi-stage dynamic pressure controlled flash evaporation device consisting of 2-3 flash chambers connected in series. The temperature and vacuum parameters of each flash chamber can be adjusted according to the light component content of the upstream material and the molecular weight requirements of the resulting intermediate product. The reaction conditions for each stage of flash evaporation are: furnace radiation section temperature 140~420℃, flash evaporator bottom temperature 120~400℃, absolute pressure 5~20kPa, and residence time 0.5~2h.

[0061] In short-path molecular distillation, the temperature of polymeric asphalt (the heavy phase product after flash distillation) in the thin-film evaporator or short-path evaporator is 300-450℃, the absolute pressure is 0.5-30kPa, and the residence time of polymeric asphalt in the thin-film evaporator or short-path evaporator is 0.5-10min.

[0062] The obtained coating agent has a softening point of 180~280℃, a TI content of 40%~75%, a QI content of 0.01%~0.5%, an ash content of 0.01%~0.05%, and a CV content of 75%~85%.

[0063] 3) The centrifugal residue obtained in step 1) is subjected to pressure filtration, oxidation stabilization, surface modification and carbonization treatment in sequence to obtain a porous carbon skeleton;

[0064] The filtration process is performed once, twice, or more than three times depending on the molecular weight requirements of the filtration product: For a molecular weight requirement of 5000~50000, a single filtration process is used; for a molecular weight requirement of 2600~5000 (excluding 5000), a double filtration process is used; for a molecular weight requirement of 200~2600 (excluding 2600), a triple or more filtration process is used; when performing two filtration processes, a single filtration process is performed first, followed by a double filtration process; when performing three or more filtration processes, a single filtration process is performed first, followed by a double filtration process, and for filtration processes exceeding three times, either a single or double filtration process is used.

[0065] The reaction conditions for the primary pressure filtration process are: extraction temperature 100~180℃, extraction time 1~8h, and sieve to obtain filter residue of 100~400 mesh; the mass ratio of primary extractant to centrifuged residue is (1~5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline;

[0066] The reaction conditions for the secondary pressure filtration process are: extraction temperature 40~80℃, extraction time 1~4h, and 200~800 mesh filter residue obtained by sieving. The mass ratio of the secondary extractant to the primary filter residue is (0.2~2):1. The secondary extractant is one or more of acetone, benzene, toluene, and xylene.

[0067] The reaction conditions for oxidative stabilization are: reaction temperature of 260~380℃ and air flow rate of 1~10 m³ / h. 3 / h, processing time is 1~8h.

[0068] Surface modification is classified into single-stage or two-stage modification reaction processes based on the structural requirements of the surface modification products.

[0069] The surface-modified product structure requires a specific surface area of ​​600~1000 m². 2 / g, excluding 1000m 2 / g, when the micropore ratio is ≥10% and the mesopore ratio is ≥30%, a one-stage modification reaction treatment is adopted;

[0070] The specific surface area of ​​the surface-modified product structure is 1000~1800 m². 2 / g, excluding 1800m 2 When the micropore content is ≥20% and the mesopore content is ≥40%, a two-stage modification reaction treatment is adopted.

[0071] The specific surface area of ​​the surface-modified product structure is 1800~2800 m². 2 When the micropore content is ≥30% and the mesopore content is ≥50%, a modification reaction of three or more stages shall be adopted.

[0072] The reaction conditions for surface modification are: reaction temperature of 300~1200℃, reaction time of 0.5~10h; the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

[0073] The reaction conditions for carbonization are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 700~1800℃, and the final temperature holding time is 1~12h.

[0074] The obtained porous carbon framework has the following properties: specific surface area of ​​800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, mesoporous content ≥30%.

[0075] 4) After the porous carbon skeleton and silicon powder are mixed evenly in a VC mixer, the coating agent obtained in step 2) is added, and the mixture is subjected to solid-phase coating and carbonization treatment to obtain a silicon-carbon anode material with low expansion rate.

[0076] The particle size distribution of the silicon powder is: D 50 5~25nm, D max ≤180nm; the mass ratio of silicon powder to porous carbon skeleton is (1~5):20.

[0077] The stirring speed of the VC mixer is 400~1200 rad / min, the stirring time is 1~12 h, and the vacuum degree is 0.01~0.09 MPa.

[0078] The reaction conditions for solid-phase coating are as follows: coating temperature is 380~760℃, heating rate is 5~10℃ / min, isothermal time is 2~8h, stirring speed is 400~1200rad / min, vacuum degree is 0.01~0.09MPa; the agent-carbon ratio is the mass ratio of the coating agent to the mixture of porous carbon skeleton and silicon powder, which is (1~4):10.

[0079] The reaction conditions for carbonization are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200 ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 1400~1800℃, and the final temperature holding time is 2~8 h.

[0080] See Figure 1 , Figure 2 The low expansion rate silicon-carbon anode material has an initial discharge specific capacity ≥450mAh / g, initial coulombic efficiency ≥88%, capacity retention ≥82% after 400 0.2C cycles, cycle performance ≥1000 cycles, rate performance ≥80% at 2C / 0.5C, and expansion rate ≤180%.

[0081] Example:

[0082] The preparation process parameters and test results of the low expansion rate silicon-carbon anode materials prepared based on porous carbon frameworks in Examples 1-5 are shown in Tables 1-3.

[0083] Table 1. Preparation process and indicators of coating agent

[0084]

[0085]

[0086] Table 2. Preparation process and indicators of carbon skeleton raw materials

[0087]

[0088]

[0089] Table 3. Preparation process and indicators of low expansion coefficient silicon-carbon anode materials

[0090]

[0091] This invention, through material structure design and preparation methods, yields a low-expansion-rate silicon-carbon anode material based on a porous carbon framework, characterized by high capacity, long cycle life, excellent rate performance, and high initial coulombic efficiency, prepared via a solid-state coating method. The resulting porous carbon framework possesses a high specific surface area and a reasonable pore distribution, effectively buffering stress changes caused by the volume expansion of silicon powder and providing expansion space during silicon powder-carbon composite processes, thus maintaining the integrity of the electrode structure. The uniform coating of the carbon layer not only reduces the specific surface area of ​​the silicon-carbon anode material but also increases lithium-ion transport channels, further improving electrochemical performance such as safe service life and rate capability. This invention addresses the main problems of existing silicon-based anode materials in practical applications and simultaneously produces a lithium-ion battery anode material coating agent, demonstrating significant technical advantages and market application potential.

Claims

1. A method for preparing low expansion rate silicon-carbon anode materials based on a porous carbon framework, characterized in that, Includes the following steps: 1) The raw oil is processed by super centrifugation to obtain centrifugal liquid and centrifugal residue; The feedstock oil has the following specifications: ash content < 0.05%, moisture content < 1.0%, and quinoline insoluble content ≥ 15%. The quinoline insoluble content includes primary organic quinoline insolubles and secondary quinoline insolubles, wherein the primary organic quinoline insoluble content is ≥ 10%, ash content < 0.05%, and particle size distribution is D. 50 : 0.5~1μm, D max : 1.5~2μm; secondary quinoline insoluble content ≥5%, ash content <0.05%, particle size distribution is D 50 5~30μm, D max : 40~50μm; The feedstock oil is one or more of the following: poor and rich coal dry distillation tar, medium and low temperature coal tar, high temperature coal tar, catalytic cracking slurry oil, and ethylene residue oil. The obtained centrifuged residue contained ≥80% toluene-insoluble matter and <0.05% ash. 2) The centrifuged liquid is separated by distillation to obtain heavy distillate oil, which is then mixed with a catalytic crosslinking agent and subjected to thermal polymerization, flash evaporation, and short-path molecular distillation to obtain a coating agent; The volume percentage of heavy distillate oil distilled at 380℃ is ≥50%, the mass percentage of heptane-insoluble components is ≥70%, the mass percentage of toluene-soluble components is ≥50%, and the mass percentage of toluene-insoluble components is ≥5%. The obtained coating agent has a softening point of 180~280℃, a TI content of 40%~75%, a QI content of 0.01%~0.5%, an ash content of 0.01%~0.05%, and a CV content of 75%~85%. 3) The centrifugal residue obtained in step 1) is subjected to pressure filtration, oxidation stabilization, surface modification and carbonization treatment in sequence to obtain a porous carbon skeleton; The surface modification is divided into one-stage modification reaction treatment or two-stage or more modification reaction treatment according to the structural requirements of the surface modification product; the reaction conditions are: reaction temperature of 300~1200℃, reaction time of 0.5~10h; the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3; 4) After the porous carbon skeleton and silicon powder are mixed evenly, the coating agent obtained in step 2) is added, and the mixture is subjected to solid-phase coating and carbonization treatment to obtain a silicon-carbon anode material with low expansion rate.

2. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, The reaction conditions for the supercentrifugation treatment in step 1) are: separation temperature 30~80℃, separation time 0.5~5h, centrifugation speed 5000~20000rad / min, and sieve mesh 100~800 mesh.

3. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, The reaction conditions for the distillation separation process in step 2) are as follows: top temperature of 160~280℃, bottom temperature of 320~400℃, vacuum degree of 0.01~0.09MPa, and recycle ratio of 0.6~1.

2.

4. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, In step 2), the catalytic crosslinking agent is one or more solvents selected from paraformaldehyde, benzaldehyde, glyoxal, glutaraldehyde, and alkylphenol resin, or a compound solvent of the solvents mentioned above. The mass ratio of the catalytic crosslinking agent to the heavy distillate oil is (1~10):

20.

5. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, The reaction conditions for thermal polymerization in step 2) are: heating rate of 5~15℃ / min, reaction temperature of 280~420℃, and treatment time of 1~8h; In step 2), the flash evaporation is a multi-stage dynamic pressure-controlled flash evaporation. The reaction conditions for each stage of flash evaporation are as follows: the temperature of the radiant section of the heating furnace is 140~420℃, the temperature of the bottom of the flash evaporator is 120~400℃, the absolute pressure is 5~20kPa, and the residence time is 0.5~2h. In the aforementioned short-path molecular distillation, the polymeric asphalt is at a temperature of 300–450°C and an absolute pressure of 0.5–30 kPa in the thin-film evaporator or short-path evaporator, and the residence time of the polymeric asphalt in the thin-film evaporator or short-path evaporator is 0.5–10 min.

6. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, In step 3), the pressure filtration process is performed once, twice, or more than three times depending on the molecular weight requirements of the filtration product. If the molecular weight of the filter press product is 5000~50000, a single filter press is used; if the molecular weight of the filter press product is 2600~5000 (excluding 5000), a double filter press is used; if the molecular weight of the filter press product is 200~2600 (excluding 2600), a triple or higher filter press is used. When the filtration process is performed twice, the first filtration process is performed first, followed by the second filtration process. When the filtration process is performed three or more times, the first filtration process is performed first, followed by the second filtration process. For filtration processes with three or more times, the process conditions of either the first or second filtration process are adopted. The reaction conditions for the primary pressure filtration process are: extraction temperature 100~180℃, extraction time 1~8h, and sieve to obtain filter residue of 100~400 mesh; the mass ratio of primary extractant to centrifuged residue is (1~5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline; The reaction conditions for the secondary pressure filtration process are: extraction temperature 40~80℃, extraction time 1~4h, and 200~800 mesh filter residue obtained by sieving. The mass ratio of the secondary extractant to the primary filter residue is (0.2~2):

1. The secondary extractant is one or more of acetone, benzene, toluene, and xylene.

7. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, The reaction conditions for oxidation stabilization in step 3) are: reaction temperature of 260~380℃ and air flow rate of 1~10m³ / h. 3 / h, processing time 1~8h; The surface-modified product structure requires a specific surface area of ​​600~1000 m². 2 / g, excluding 1000m 2 / g, when the micropore ratio is ≥10% and the mesopore ratio is ≥30%, a one-stage modification reaction treatment is adopted; The specific surface area of ​​the surface-modified product structure is 1000~1800 m². 2 / g, excluding 1800m 2 When the micropore content is ≥20% and the mesopore content is ≥40%, a two-stage modification reaction treatment is adopted. The specific surface area of ​​the surface-modified product structure is 1800~2800 m². 2 / g, when the micropore content is ≥30% and the mesopore content is ≥50%, a three-stage or more modification reaction treatment shall be adopted; The reaction conditions for the carbonization treatment are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 700~1800℃, and the final temperature holding time is 1~12h. The porous carbon framework obtained in step 3) has the following properties: specific surface area of ​​800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, mesoporous content ≥30%.

8. The method for preparing low expansion rate silicon-carbon anode material based on a porous carbon framework according to claim 1, characterized in that, The particle size distribution of the silicon powder in step 4) is: D 50 5~25nm, D max ≤180nm; The mass ratio of the silicon powder to the porous carbon skeleton is (1~5):20; The mixing process is carried out using a VC mixer with a mixing speed of 400~1200 rad / min, a mixing time of 1~12 h, and a vacuum degree of 0.01~0.09 MPa. The reaction conditions for solid-phase coating are as follows: coating temperature is 380~760℃, heating rate is 5~10℃ / min, isothermal time is 2~8h, stirring speed is 400~1200rad / min, vacuum degree is 0.01~0.09MPa; the agent-carbon ratio is the mass ratio of the coating agent to the mixture of porous carbon skeleton and silicon powder, which is (1~4):

10. The reaction conditions for the carbonization treatment are as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the heating rate is 1~10℃ / min, the carbonization temperature is 1400~1800℃, and the final temperature holding time is 2~8h.

9. A low-expansion-rate silicon-carbon anode material prepared based on a porous carbon framework using the preparation method described in claim 1, characterized in that, The low expansion rate silicon-carbon anode material has an initial discharge specific capacity ≥450mAh / g, initial coulombic efficiency ≥88%, capacity retention ≥82% after 400 0.2C cycles, cycle performance ≥1000 cycles, rate performance ≥80% at 2C / 0.5C, and volume expansion rate ≤180%.

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