Amorphous conductive carbon skeleton for core-shell type silicon-carbon negative electrode material and preparation method of amorphous conductive carbon skeleton

Abstract

The invention belongs to the technical field of negative electrode materials, and particularly relates to an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material and a preparation method, and the preparation method comprises the following steps: 1) carrying out super centrifugal treatment on raw oil to obtain heavy centrifugal slag; (2) carrying out filter pressing treatment on the heavy centrifugal residues and an extracting agent to remove small molecular soluble substances, so as to obtain a carbon skeleton raw material; and 3) sequentially carrying out oxidation stabilization, modification treatment and carbonization treatment on the carbon skeleton raw material to obtain the amorphous conductive carbon skeleton for the core-shell type silicon-carbon negative electrode material. The amorphous conductive carbon skeleton for the core-shell type silicon-carbon negative electrode material has the advantages of low density, large specific surface area, reasonable pore size distribution and excellent conductivity. The silicon powder has excellent conductivity and relatively strong mechanical property, can buffer stress change caused by silicon volume expansion, can provide an expansion space for the silicon powder and the silicon powder in a compounding process, buffers volume expansion, and maintains the integrity of an electrode structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to an amorphous conductive carbon skeleton for core-shell silicon-carbon negative electrode materials and a preparation method thereof. Background Art

[0002] With the increasing severity of environmental problems, the depletion of fossil energy, and the widespread use and rapid development of various portable electronic products and electric vehicles, the demand for chemical energy and performance requirements are also constantly increasing. Lithium-ion batteries are currently a research hotspot in the new energy field due to their excellent properties such as high specific energy, low self-discharge, high operating voltage, no memory effect, and environmental friendliness. The anode materials currently used in commercial lithium-ion battery production are mainly 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 limiting their application range. Silicon has a large theoretical specific capacity (4200mAh / g), an order of magnitude higher than the specific capacity of graphite anode materials (372mAh / g), and a lower lithium insertion potential. Silicon has low reactivity with electrolytes, abundant reserves in the Earth's crust, and low price, making it an ideal choice for the anode material of the next generation of lithium-ion batteries.

[0003] Silicon-carbon composite material is a type of silicon-based composite material. It has attracted the attention of more and more researchers with its unique advantages and potential. Silicon and carbon have similar chemical properties, and carbon-based negative electrode materials have little volume change during charging and discharging, and have good cycle stability and conductivity. Therefore, carbon-based materials are often used as the preferred matrix for composite with silicon. In order to further improve the electrochemical properties of silicon-carbon composite materials such as cycle stability and reversible cycle capacity retention when used as negative electrode materials for lithium-ion batteries, so as to obtain a new generation of lithium-ion battery negative electrode materials that can replace graphite, researchers have conducted a lot of exploratory research in recent years and achieved remarkable results. Continuing to develop silicon-carbon composite materials with excellent performance is of great significance for their application in actual production.

[0004] Prior art patent publication number CN107394137A discloses a method for preparing a high-performance silicon-carbon anode material. The method involves dissolving a phenolic resin and a curing agent in a solvent and stirring and dissolving them in an ultrasonic stirrer. Graphite, a conductive agent, and nano-Si powder are then added to the solution in sequence. The resulting mixture is spray-dried, collected, and graded. The collected powder and asphalt are then added to a heating mixer, heated and mixed, and cooled to room temperature. Finally, the silicon-carbon anode material is sieved and graded. Phenolic resin is used as the coating carbon source. After curing, the resin provides a skeletal support, preventing the carbon source from falling off the powder surface during the asphalt coating process. Furthermore, the phenolic resin cured product has a high carbon residue rate and excellent morphology retention, effectively coating the Si and preventing Si exposure. However, the compatibility of the phenolic resin with silicon powders of varying particle sizes was not investigated. During the compounding process, Si powder expands, and the phenolic resin cannot maintain the integrity of the electrode structure. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a spherical porous amorphous conductive carbon skeleton and a preparation method for core-shell silicon-carbon negative electrode materials. The preparation process is simple, and the prepared amorphous conductive carbon skeleton 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 the stress changes caused by the volume expansion of silicon.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material comprises the following steps:

[0008] 1) Super centrifugation of the crude oil to obtain heavy centrifugal residue;

[0009] 2) The heavy centrifugal residue and the extractant are subjected to filter pressing to remove small soluble molecules to obtain a carbon skeleton raw material;

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

[0011] The raw oil is any one of rich coal dry distillation tar, catalytic cracking slurry, ethylene residue, medium and low temperature coal tar, high temperature coal tar, or a mixture of two or more thereof; the raw oil index is: ash content <0.05%, moisture <1.0%, quinoline insoluble matter content ≥15%; the quinoline insoluble matter includes primary organic quinoline insoluble matter and secondary quinoline insoluble matter, the primary organic quinoline insoluble matter in the quinoline insoluble matter content ≥10%, ash content <0.05%, and particle size distribution D 50 :0.5~1μm、D max: 1.5~2μm; the content of secondary quinoline insoluble matter in quinoline insoluble matter is ≥5%, ash content is <0.05%, and the particle size distribution is D 50 :5~30μm、D max : 40~50μm.

[0012] The reaction conditions of the ultracentrifugation treatment in step 1) are: separation temperature 30-80°C, separation time 0.5-5h, centrifugal speed 5000-20000 rad / min, and sieving to obtain heavy centrifugal residue with a particle size of 100-800 mesh.

[0013] The toluene insoluble matter content in the heavy centrifugal residue is ≥80%, and the ash content is <0.05%.

[0014] The filter press treatment is performed once or multiple times; when the filter press treatment is performed twice, the filter press treatment is performed once and then the filter press treatment is performed twice; when the filter press treatment is performed three or more times, the filter press treatment is performed once and then the filter press treatment is performed twice, and the filter press treatments for more than three times adopt the process conditions of the single filter press treatment or the secondary filter press treatment;

[0015] The reaction conditions for the primary filter press treatment are as follows: an extraction temperature of 100-180°C, an extraction time of 1-8 hours, and a sieve mesh size of 100-400; the filter residue obtained by screening is a carbon skeleton raw material; the mass ratio of the primary extractant to the heavy centrifugal residue is (1-5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline;

[0016] A primary filter press treatment is performed before a secondary filter press treatment. The reaction conditions of the secondary filter press treatment are as follows: an extraction temperature of 40-80°C, an extraction time of 1-4 hours, and a sieve mesh size of 200-800; the filter residue obtained by screening is a carbon skeleton raw material; the mass ratio of the secondary extractant to the upper filter residue is (0.2-2):1; and the secondary extractant is one or more of acetone, benzene, toluene, and xylene.

[0017] The mass percentage of β resin in the carbon skeleton raw material in step 2) is 0.5% to 10%, and the ash content is less than 0.05%.

[0018] The reaction conditions of the oxidation stabilization in step 3) are: reaction temperature of 260-380°C, air flow of 1-10m 3 / h, processing time is 1~8h.

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

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

[0021] An amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material, wherein the specific surface area of ​​the amorphous conductive carbon skeleton for the silicon-carbon negative electrode is 800-2000 m 2 / g, pore volume is 0.4~1.4cm 3 / g, average pore size is 1~120nm, mesopore occupancy is ≥30%, and true density is 1.50~2.0g / cm 3 , tap density ≥0.6g / cm 3 , ash content <0.05%, particle size distribution is D10: 2~5μm, D 50 :40~50μm、D max : 70~80μm, and the interlayer spacing is 0.34nm~0.36nm.

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

[0023] 1) The core-shell silicon-carbon negative electrode material of the present invention has a low density, a large specific surface area, a reasonable pore size distribution, and excellent conductivity. Its indicators are: a specific surface area of ​​800~2000m 2 / g, pore volume is 0.4~1.4cm 3 / g, average pore size is 1~120nm, mesopore occupancy is ≥30%, and true density is 1.50~2.0g / cm 3 , tap density ≥0.6g / cm 3 , ash content <0.05%, D 50 4~80μm, interlayer spacing (d 002 ) is 0.34nm~0.36nm, and the conductivity is >10S / cm.

[0024] 2) The carbon skeleton raw material obtained in the preparation process of the present invention is spherical loose particles. During the modification process, there is no need to mix with an active agent, grind, or impregnate. The preparation process is simple and the performance is safe and reliable.

[0025] 3) The amorphous conductive carbon framework used in the core-shell silicon-carbon anode material of this invention exhibits excellent conductivity and strong mechanical properties. It can buffer the stress changes caused by silicon volume expansion, providing expansion space for silicon powder during compounding, buffering volume expansion and maintaining the integrity of the electrode structure. The resulting core-shell silicon-carbon anode material has a volume expansion rate of ≤120% and an energy density of ≥280Wh / kg.

[0026] 4) By adjusting the filter press treatment and modification process, the present invention can control the structural parameters of the spherical porous carbon skeleton, such as pore volume, pore diameter, and interlayer spacing, improve the compatibility with silicon powders of different particle sizes, and further optimize the electrochemical performance of the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a 5000x scanning electron microscope structure diagram of the amorphous conductive carbon skeleton used in core-shell silicon-carbon negative electrode materials.

[0028] Figure 2 This is a 20,000x scanning electron microscope structure diagram of the amorphous conductive carbon skeleton used in core-shell silicon-carbon negative electrode materials.

[0029] Figure 3 This is a polarized microstructure diagram of the amorphous conductive carbon skeleton used in core-shell silicon-carbon negative electrode materials. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below, 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 skeleton used in core-shell silicon-carbon negative electrode materials is 800~2000m 2 / g, pore volume is 0.4~1.4cm 3 / g, average pore size is 1~120nm, mesopore occupancy is ≥30%, and true density is 1.50~2.0g / cm 3 , tap density ≥0.6g / cm 3 , ash content <0.05%, particle size distribution is D 10 :2~5μm、D 50 :40~50μm、D max : 70~80μm, interlayer spacing is 0.34nm~0.36nm, see Figure 1-Figure 3 .

[0032] The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material comprises the following steps:

[0033] 1) Super centrifugation of the crude oil to obtain heavy centrifugal residue;

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

[0035] The reaction conditions of the ultracentrifugation treatment are: separation temperature 30-80°C, separation time 0.5-5h, centrifugal speed 5000-20000 rad / min, sieving to obtain heavy centrifugal residue of 100-800 mesh.

[0036] The toluene insoluble matter content in the obtained heavy centrifugal residue is ≥80%, and the ash content is <0.05%.

[0037] 2) The heavy centrifugal residue and the extractant are subjected to filter pressing to remove small soluble molecules to obtain a carbon skeleton raw material;

[0038] The filter press treatment is carried out once, twice or more than three times according to the molecular weight requirements of the filter press product: if the molecular weight requirement of the filter press product is 5000~50000, one filter press treatment is adopted; if the molecular weight requirement of the filter press product is 2600~5000, excluding 5000, two filter press treatments are adopted; if the molecular weight requirement of the filter press product is 200~2600, excluding 2600, three or more filter press treatments are adopted.

[0039] When the filter press treatment is performed twice, the filter press treatment is performed once and then the filter press treatment is performed twice; when the filter press treatment is performed three or more times, the filter press treatment is performed once and then the filter press treatment is performed twice. The filter press treatments for more than three times adopt the process conditions of the single filter press treatment or the double filter press treatment.

[0040] The reaction conditions of the primary filter press treatment are as follows: extraction temperature 100-180°C, extraction time 1-8 hours, mesh size 100-400; the filter residue obtained by screening is the carbon skeleton raw material; the mass ratio of the primary extractant to the centrifugal residue is (1-5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline.

[0041] The reaction conditions of the secondary filter press treatment are: extraction temperature 40~80℃, extraction time 1~4h, sieve mesh size 200~800; the filter residue obtained by screening is the carbon skeleton raw material, the mass ratio of the secondary extractant to the upper filter residue is (0.2~2):1; the secondary extractant is one or more of acetone, benzene, toluene, and xylene.

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

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

[0044] The reaction conditions for oxidation stabilization are: reaction temperature 260~380℃, air flow rate 1~10m 3 / h, processing time is 1~8h.

[0045] The modification process is divided into one-stage modification process or two or more-stage modification process according to the structural requirements of the modified product:

[0046] The modified product structure requires a specific surface area of ​​600~1000m 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 1000~1800m 2 / g, excluding 1800m 2 / g, when the proportion of micropores is ≥20% and the proportion of mesopores is ≥40%, a two-stage modification reaction treatment is adopted;

[0048] The specific surface area of ​​the modified product structure is 1800~2800m 2 / g, when the proportion of micropores is ≥30% and the proportion of mesopores is ≥50%, more than three stages of modification reaction treatment are adopted.

[0049] The modification treatment is a one-stage or multi-stage treatment, the reaction temperature is 300-1200°C, the reaction time is 0.5-10h, and the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

[0050] The carbonization treatment 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 constant temperature is maintained for 1~12h.

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

[0052] The silicon-carbon negative electrode is made by mixing an amorphous conductive carbon skeleton with silicon powder, grinding the mixture and then mixing it with coating asphalt. After coating and calcining, a core-shell silicon-carbon negative electrode 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 negative electrode materials of Examples 1 to 5 are shown in Tables 1 and 2.

[0055] Table 1 Carbon skeleton raw material preparation process and indicators

[0056]

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

[0058]

[0059] The amorphous conductive carbon skeleton used in the core-shell silicon-carbon negative electrode material of the present invention has a low density, a large specific surface area, and a reasonable pore size distribution. The carbon skeleton raw material used in the preparation process is spherical, loose particles, and the modification process does not require mixing with an active agent, grinding, or impregnation. The preparation process is simple and the performance is safe and reliable. The carbon skeleton has excellent conductivity and strong mechanical properties, and can buffer the stress changes caused by silicon volume expansion. It can provide expansion space for silicon powder during the composite process, buffering volume expansion and maintaining the integrity of the electrode structure.

Claims

1. A method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material, characterized in that: The following steps are involved: 1) Super centrifugation of the crude oil to obtain heavy centrifugal residue; 2) The heavy centrifugal residue and the extractant are subjected to filter pressing to remove small soluble molecules to obtain a carbon skeleton raw material; 3) The carbon skeleton raw material is subjected to oxidation stabilization, modification treatment, and carbonization treatment in sequence to obtain an amorphous conductive carbon skeleton for core-shell silicon-carbon negative electrode material.

2. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The raw oil is any one of rich coal dry distillation tar, catalytic cracking slurry, ethylene residue, medium and low temperature coal tar, high temperature coal tar, or a mixture of two or more thereof; the raw oil index is: ash content <0.05%, moisture <1.0%, quinoline insoluble matter content ≥15%; the quinoline insoluble matter includes primary organic quinoline insoluble matter and secondary quinoline insoluble matter, the primary organic quinoline insoluble matter in the quinoline insoluble matter content ≥10%, ash content <0.05%, and particle size distribution D 50 :0.5~1μm、D max : 1.5~2μm; the content of secondary quinoline insoluble matter in quinoline insoluble matter is ≥5%, ash content is <0.05%, and the particle size distribution is D 50 :5~30μm、D max : 40~50μm.

3. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The reaction conditions of the ultracentrifugation treatment in step 1) are: separation temperature 30-80°C, separation time 0.5-5h, centrifugal speed 5000-20000 rad / min, and sieving to obtain heavy centrifugal residue with a particle size of 100-800 mesh.

4. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The toluene insoluble matter content in the heavy centrifugal residue is ≥80%, and the ash content is <0.05%.

5. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The filter press treatment is performed once or multiple times; when the filter press treatment is performed twice, the filter press treatment is performed once and then the filter press treatment is performed twice; when the filter press treatment is performed three or more times, the filter press treatment is performed once and then the filter press treatment is performed twice, and the filter press treatments for more than three times adopt the process conditions of the single filter press treatment or the secondary filter press treatment; The reaction conditions for the primary filter press treatment are as follows: an extraction temperature of 100-180°C, an extraction time of 1-8 hours, and a sieve mesh size of 100-400; the filter residue obtained by screening is the carbon skeleton raw material; the mass ratio of the primary extractant to the heavy centrifugal residue is (1-5):1; the primary extractant is one or more of wash oil, pyridine, and quinoline; A primary filter press treatment is performed before a secondary filter press treatment. The reaction conditions of the secondary filter press treatment are as follows: an extraction temperature of 40-80°C, an extraction time of 1-4 hours, and a sieve mesh size of 200-800; the filter residue obtained by screening is a carbon skeleton raw material; the mass ratio of the secondary extractant to the upper filter residue is (0.2-2):1; and the secondary extractant is one or more of acetone, benzene, toluene, and xylene.

6. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The mass percentage of β resin in the carbon skeleton raw material in step 2) is 0.5% to 10%, and the ash content is less than 0.05%.

7. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The reaction conditions of the oxidation stabilization in step 3) are: reaction temperature of 260-380°C, air flow of 1-10m 3 / h, processing time is 1~8h.

8. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The modification treatment in step 3) is a one-stage or multi-stage treatment, the reaction temperature is 300-1200°C, the reaction time is 0.5-10h, and the modifier is one of water, CO2, KOH, K2CO3, NaOH, and Na2CO3.

9. The method for preparing an amorphous conductive carbon skeleton for a core-shell silicon-carbon negative electrode material according to claim 1, characterized in that: The carbonization treatment in step 3) is as follows: under nitrogen protection, the nitrogen flow rate is 300-1200 ml / min, the temperature is increased to 700-1800°C at a heating rate of 1-10°C / min, and the constant temperature is maintained for 1-12 hours.

10. An amorphous conductive carbon skeleton for core-shell silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The specific surface area of ​​the amorphous conductive carbon skeleton used for the silicon-carbon negative electrode is 800~2000m 2 / g, pore volume is 0.4~1.4cm 3 / g, average pore size is 1~120nm, mesopore occupancy is ≥30%, and true density is 1.50~2.0g / cm 3 , tap density ≥0.6g / cm 3 , ash content <0.05%, particle size distribution is D 10 :2~5μm、D 50 :40~50μm、D max : 70~80μm, and the interlayer spacing is 0.34nm~0.36nm.

Images