An amorphous conductive carbon framework for core-shell silicon-carbon negative electrode materials and a preparation method thereof

Abstract

The present application belongs to the technical field of negative electrode materials, and particularly relates to an amorphous conductive carbon framework for a core-shell silicon-carbon negative electrode material and a preparation method thereof, comprising the following steps: 1) subjecting raw oil to super centrifugal treatment to obtain heavy centrifugal residue; 2) removing small molecule solubles by pressure filtration treatment of the heavy centrifugal residue and an extractant to obtain a carbon framework raw material; and 3) subjecting the carbon framework raw material to oxidation stabilization, modification treatment and carbonization treatment in sequence to obtain the amorphous conductive carbon framework for the core-shell silicon-carbon negative electrode material. The amorphous conductive carbon framework for the core-shell silicon-carbon negative electrode material has the advantages of low bulk density, large specific surface area, reasonable pore size distribution and excellent electrical conductivity. The amorphous conductive carbon framework has excellent electrical conductivity and strong mechanical properties, can buffer the stress change caused by the volume expansion of silicon, can provide expansion space during the compounding of silicon powder and the amorphous conductive carbon framework, can buffer the volume expansion, and can maintain the integrity of the electrode structure.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, and particularly relates to an amorphous conductive carbon skeleton for core-shell silicon-carbon anode materials and its preparation method. Background Technology

[0002] With the increasing severity of environmental problems, the depletion of fossil fuels, and 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, due to their superior performance such as high specific energy, low self-discharge, high operating voltage, no memory effect, and environmental friendliness, have become a research hotspot in the current new energy field. Currently, the main anode materials for commercially produced lithium-ion batteries 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 (4200 mAh / g), which is an order of magnitude higher than that of graphite anode materials (372 mAh / g) and has a lower lithium intercalation potential. Silicon has low reactivity with electrolytes, is abundant in the earth's crust, and is inexpensive, making it an ideal choice for next-generation 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 CN107394137A discloses a method for preparing a high-performance silicon-carbon anode material. First, phenolic resin and a curing agent are dissolved in a solvent and stirred in an ultrasonic stirrer. Then, graphite, a conductive agent, and nano-Si powder are added sequentially to the solution. The resulting mixture is spray-dried, collected, and graded. The collected powder and asphalt are added to a heated mixer, heated and mixed, and cooled to room temperature. Finally, the mixture is sieved and graded to obtain the silicon-carbon anode material. Using phenolic resin as the carbon source for coating, the resin, after curing, can act as a skeletal support, preventing the carbon source from detaching from the powder surface during the asphalt coating process. Furthermore, the cured phenolic resin has a high residual carbon rate and good morphology retention of the carbonized material, resulting in good Si coating and preventing Si exposure. However, this method did not investigate the compatibility of phenolic resin with silicon powder of different particle sizes. During the Si powder-solubilization process, volume expansion occurs, and the phenolic resin cannot maintain the integrity of the electrode structure. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a spherical porous amorphous conductive carbon framework for core-shell silicon-carbon anode materials and its preparation method. The preparation process is simple, and the prepared amorphous conductive carbon framework has low bulk density, large specific surface area, reasonable pore size distribution, and excellent conductivity. It has excellent conductivity and strong mechanical properties and can buffer stress changes caused by silicon volume expansion.

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

[0007] A method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material includes the following steps:

[0008] 1) The raw oil is subjected to supercentrifugation to obtain heavy centrifugal residue;

[0009] 2) The heavy centrifuged residue and extractant are subjected to pressure filtration to remove small molecule soluble substances, thereby obtaining carbon skeleton raw materials;

[0010] 3) The carbon skeleton raw material is subjected to oxidation stabilization, modification and carbonization treatment in sequence to obtain the amorphous conductive carbon skeleton for core-shell silicon-carbon anode material.

[0011] The feedstock oil is any one or a mixture of two or more of the following: rich coal dry distillation tar, catalytic cracking slurry oil, ethylene residue oil, medium- and low-temperature coal tar, and high-temperature coal tar. The feedstock oil specifications are: 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, with the primary organic quinoline insoluble content ≥ 10%, ash content < 0.05%, and particle size distribution D. 50 : 0.5~1μm, D max: 1.5~2μm; secondary quinoline insoluble matter content ≥5% in quinoline insoluble matter, ash content <0.05%, particle size distribution D 50 5~30μm, D max : 40~50μm.

[0012] 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, sieve to obtain heavy centrifuged residue with a particle size of 100~800 mesh.

[0013] The heavy centrifuged residue contains ≥80% toluene-insoluble matter and <0.05% ash.

[0014] The pressure filtration process can be performed once or multiple times. When the pressure filtration process is performed twice, the first pressure filtration process is performed first, followed by the second pressure filtration process. When the pressure filtration process is performed three or more times, the first pressure filtration process is performed first, followed by the second pressure filtration process. For pressure filtration processes of three or more times, the process conditions of one or two pressure filtration processes are adopted.

[0015] The reaction conditions for primary pressure filtration are: extraction temperature 100~180℃, extraction time 1~8h, and sieve mesh size 100~400; the filter residue obtained by sieving is a carbon skeleton raw material; the mass ratio of primary extractant to heavy centrifuged residue is (1~5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline.

[0016] Before the secondary pressure filtration process, a primary pressure filtration process is performed. The reaction conditions for the secondary pressure filtration process are: extraction temperature 40~80℃, extraction time 1~4h, and sieve mesh size 200~800. The filter residue obtained by sieving is a carbon skeleton raw material. 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.

[0017] In step 2), the carbon skeleton raw material contains 0.5% to 10% β resin by mass and <0.05% ash.

[0018] 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 is 1~8h.

[0019] In step 3), the modification treatment is a one-stage or multi-stage treatment, the reaction temperature is 300~1200℃, the reaction time is 0.5~10h, and the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

[0020] The carbonization process in step 3) is as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the temperature is increased to 700~1800℃ at a heating rate of 1~10℃ / min, and the temperature is maintained for 1~12h.

[0021] An amorphous conductive carbon framework for core-shell silicon-carbon anode materials, wherein the specific surface area of ​​the amorphous conductive carbon framework for silicon-carbon anodes is 800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, average pore size 1~120nm, mesopore occupancy ≥30%, true density 1.50~2.0g / cm³ 3 Tap density ≥ 0.6 g / cm³ 3 Ash content <0.05%, particle size distribution is D10: 2~5μm, D 50 40~50μm, D max 70~80μm, interlayer spacing is 0.34nm~0.36nm.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1) The core-shell silicon-carbon anode material of this invention uses an amorphous conductive carbon framework with low bulk density, large specific surface area, reasonable pore size distribution, and excellent conductivity. Its specifications include a specific surface area of ​​800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, average pore size 1~120nm, mesopore occupancy ≥30%, true density 1.50~2.0g / cm³ 3 Tap density ≥ 0.6 g / cm³ 3 Ash content <0.05%, D 50 The interlayer spacing is 4~80μm. 002 The wavelength range is 0.34 nm to 0.36 nm, and the conductivity is >10 S / cm.

[0024] 2) The carbon skeleton raw material obtained in the preparation process of this invention is a spherical loose particle. It does not require mixing, grinding or impregnation with activator during the modification process. The preparation process is simple and the performance is safe and reliable.

[0025] 3) The amorphous conductive carbon skeleton used in the core-shell silicon-carbon anode material of this invention has excellent conductivity and strong mechanical properties. It can buffer the stress changes caused by the volume expansion of silicon, provide expansion space for silicon powder during the composite process, buffer volume expansion, and maintain the integrity of the electrode structure. The volume expansion rate of the core-shell silicon-carbon anode material product made from it is ≤120%, and the energy density is ≥280Wh / kg.

[0026] 4) By adjusting the pressure filtration and modification processes, this invention can control the structural parameters such as pore volume, pore size, and interlayer spacing of the spherical porous carbon framework, improve the compatibility with silicon powder of different particle sizes, and further optimize the electrochemical performance of silicon-carbon anode materials. Attached Figure Description

[0027] Figure 1 This is a 5000x scanning electron microscope (SEM) image of the amorphous conductive carbon skeleton used in core-shell silicon-carbon anode materials.

[0028] Figure 2 This is a 20,000x scanning electron microscope (SEM) image of the amorphous conductive carbon skeleton used in core-shell silicon-carbon anode materials.

[0029] Figure 3 This is a polarized light microstructure diagram of the amorphous conductive carbon skeleton used in core-shell silicon-carbon anode materials. Detailed Implementation

[0030] 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.

[0031] The specific surface area of ​​the amorphous conductive carbon framework used in core-shell silicon-carbon anode materials is 800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, average pore size 1~120nm, mesopore occupancy ≥30%, true density 1.50~2.0g / cm³ 3 Tap density ≥ 0.6 g / cm³ 3 Ash content <0.05%, particle size distribution D 10 2~5μm, D 50 40~50μm, D max 70~80μm, interlayer spacing 0.34nm~0.36nm, see Figures 1-3 .

[0032] A method for preparing an amorphous conductive carbon framework for core-shell silicon-carbon anode materials includes the following steps:

[0033] 1) The raw oil is subjected to supercentrifugation to obtain heavy centrifugal residue;

[0034] The feedstock oil has an ash content of <0.05%, a moisture content of <1.0%, and a quinoline-insoluble content of ≥15%. The quinoline-insoluble content includes primary organic quinoline insolubles and secondary quinoline insolubles. The primary organic quinoline insolubles have a content of ≥10%, an ash content of <0.05%, and a particle size distribution of D. 50 : 0.5~1μm, D max : 1.5~2μm; secondary quinoline insoluble matter content ≥5% in quinoline insoluble matter, ash content <0.05%, particle size distribution D50 5~30μm, D max 40~50μm. The feedstock is any one or a mixture of two or more of the following: rich coal dry distillation tar, catalytic cracking slurry oil, ethylene residue oil, medium and low temperature coal tar, and high temperature coal tar.

[0035] The reaction conditions for supercentrifugation are: separation temperature 30~80℃, separation time 0.5~5h, centrifugation speed 5000~20000rad / min, sieved to obtain 100~800 mesh heavy centrifugal residue.

[0036] The obtained heavy centrifuged residue contains ≥80% toluene-insoluble matter and <0.05% ash.

[0037] 2) The heavy centrifuged residue and extractant are subjected to pressure filtration to remove small molecule soluble substances, thereby obtaining carbon skeleton raw materials;

[0038] The filtration process is carried out in one, two, or more than three stages depending on the molecular weight requirements of the filtration product: if the molecular weight requirement of the filtration product is 5000~50000, a single filtration process is used; if the molecular weight requirement of the filtration product is 2600~5000 (excluding 5000), a two-stage filtration process is used; if the molecular weight requirement of the filtration product is 200~2600 (excluding 2600), a three-stage or more filtration process is used.

[0039] 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 of three or more times, the process conditions of either the first or second filtration process are adopted.

[0040] The reaction conditions for primary pressure filtration are: extraction temperature 100~180℃, extraction time 1~8h, and sieve mesh size 100~400; the filter residue obtained by sieving is a carbon skeleton raw material; 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.

[0041] The reaction conditions for the secondary pressure filtration treatment are: extraction temperature 40~80℃, extraction time 1~4h, and sieve mesh size 200~800; the filter residue obtained by sieving is a carbon skeleton raw material, and 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.

[0042] The β resin content (mass percentage) in the carbon skeleton raw material is 0.5%~10%, and the ash content is <0.05%.

[0043] 3) The carbon skeleton raw material is subjected to oxidation stabilization, modification and carbonization treatment in sequence to obtain the amorphous conductive carbon skeleton for core-shell silicon-carbon anode material.

[0044] 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.

[0045] The modification process is divided into one-stage modification process or two-stage or more modification processes, depending on the structural requirements of the modified product:

[0046] The 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;

[0047] The specific surface area of ​​the 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.

[0048] The specific surface area of ​​the 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.

[0049] The modification process can be carried out in one or more stages, with a reaction temperature of 300~1200℃ and a reaction time of 0.5~10h. The modifier is one of water, CO2, KOH, K2CO3, NaOH, or Na2CO3.

[0050] The carbonization process is as follows: under nitrogen protection, the nitrogen flow rate is 300~1200 ml / min, the temperature is increased to 700~1800℃ at a heating rate of 1~10℃ / min, and then kept constant for 1~12 hours.

[0051] Preparation of core-shell silicon-carbon anode materials:

[0052] The silicon-carbon anode is made by mixing an amorphous conductive carbon skeleton with silicon powder, grinding it, and then mixing it with coated asphalt. After coating and calcination, a core-shell silicon-carbon anode material is obtained.

[0053] Example:

[0054] The preparation process parameters and test results of the amorphous conductive carbon skeleton for the core-shell silicon-carbon anode materials in Examples 1-5 are shown in Tables 1 and 2.

[0055] Table 1. Preparation process and indicators of carbon skeleton raw materials

[0056]

[0057] Table 2. Preparation process and indicators of amorphous conductive carbon skeleton for silicon-carbon anodes

[0058]

[0059] The core-shell silicon-carbon anode material of this invention utilizes an amorphous conductive carbon skeleton with low bulk density, large specific surface area, and reasonable pore size distribution. The carbon skeleton raw material used in the preparation process is a near-spherical, loose particle, eliminating the need for mixing, grinding, or impregnation with activators during modification. This simplifies the preparation process and ensures safe and reliable performance. The carbon skeleton possesses excellent conductivity and strong mechanical properties, effectively buffering stress changes caused by silicon volume expansion. It provides expansion space during the silicon-carbon composite process, thus buffering volume expansion and maintaining the integrity of the electrode structure.

Claims

1. A method for preparing an amorphous conductive carbon framework for core-shell silicon-carbon anode materials, characterized in that, Includes the following steps: 1) The raw oil is subjected to supercentrifugation to obtain heavy centrifugal residue; the raw oil has the following properties: ash content <0.05%, moisture content <1.0%, and quinoline insoluble content ≥15%; the supercentrifugation conditions are: separation temperature 30~80℃, separation time 0.5~5h, centrifugation speed 5000~20000rad / min, and sieved to obtain heavy centrifugal residue with a particle size of 100~800 mesh; the heavy centrifugal residue has a toluene insoluble content ≥80% and an ash content <0.05%; 2) The heavy centrifuged residue and extractant are subjected to pressure filtration to remove small molecule soluble substances, thereby obtaining carbon skeleton raw materials; The pressure filtration process can be performed once or multiple times. When the pressure filtration process is performed twice, the first pressure filtration process is performed first, followed by the second pressure filtration process. When the pressure filtration process is performed three or more times, the first pressure filtration process is performed first, followed by the second pressure filtration process. For pressure filtration processes of three or more times, the process conditions of one or two pressure filtration processes are adopted. The reaction conditions for primary pressure filtration are: extraction temperature 100~180℃, extraction time 1~8h, and sieve mesh size 100~400; the filter residue obtained by sieving is a carbon skeleton raw material; the mass ratio of primary extractant to heavy centrifuged residue is (1~5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline. Before the secondary pressure filtration, a primary pressure filtration is performed. The reaction conditions for the secondary pressure filtration are: extraction temperature 40~80℃, extraction time 1~4h, and sieve mesh size 200~800. The filter residue obtained by sieving is a carbon skeleton raw material. 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. 3) The carbon skeleton raw material is subjected to oxidation stabilization, modification and carbonization treatment in sequence to obtain the amorphous conductive carbon skeleton for core-shell silicon-carbon anode material. The specific surface area of ​​the amorphous conductive carbon framework used in the silicon-carbon anode is 800~2000 m². 2 / g, pore volume 0.4~1.4cm 3 / g, average pore size 1~120nm, mesopore occupancy ≥30%, true density 1.50~2.0g / cm³ 3 Tap density ≥ 0.6 g / cm³ 3 Ash content <0.05%, particle size distribution D 10 2~5μm, D 50 40~50μm, D max 70~80μm, interlayer spacing is 0.34nm~0.36nm.

2. The method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material according to claim 1, characterized in that, The feedstock oil is any one or a mixture of two or more of the following: rich coal dry distillation tar, catalytic cracking slurry oil, ethylene residue oil, medium- and low-temperature coal tar, and high-temperature coal tar; the quinoline insolubles include primary organic quinoline insolubles and secondary quinoline insolubles, wherein the content of primary organic quinoline insolubles is ≥10%, the ash content is <0.05%, and the particle size distribution is D. 50 : 0.5~1μm, D max : 1.5~2μm; secondary quinoline insoluble matter content ≥5% in quinoline insoluble matter, ash content <0.05%, particle size distribution D 50 5~30μm, D max : 40~50μm.

3. The method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material according to claim 1, characterized in that, In step 2), the carbon skeleton raw material contains 0.5% to 10% β resin by mass and <0.05% ash.

4. The method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material 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 is 1~8h.

5. The method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material according to claim 1, characterized in that, In step 3), the modification treatment is a one-stage or multi-stage treatment, the reaction temperature is 300~1200℃, the reaction time is 0.5~10h, and the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

6. The method for preparing an amorphous conductive carbon framework for a core-shell silicon-carbon anode material according to claim 1, characterized in that, The carbonization process in step 3) is as follows: under nitrogen protection, the nitrogen flow rate is 300~1200ml / min, the temperature is increased to 700~1800℃ at a heating rate of 1~10℃ / min, and the temperature is maintained for 1~12h.

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