A silicon-carbon composite material based on a three-dimensional network silicon-carbon structure, its preparation method and application

Abstract

This invention discloses a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, its preparation method, and its application. The silicon-carbon composite material consists of a three-dimensional network structure composed of nano-silicon and carbon, and a carbon coating layer disposed on the outside of the three-dimensional network structure. The three-dimensional network structure uses a carbon structure as a skeleton, and the nano-silicon is uniformly embedded on the carbon skeleton. In the preparation process, the nano-silicon and a high-volatile organic carbon source are first mixed evenly and then subjected to isostatic pressing treatment. After crushing, it is sintered once, and then sintered again with a carbon coating agent. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure can be obtained. This invention overcomes the technical problems of large volume change of silicon-based anode materials, particle pulverization of silicon materials, and repeated growth of surface SEI film. The preparation process is simple, the equipment is mature, and it is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of silicon-based anode materials for lithium-ion batteries, and particularly relates to a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, its preparation method, and its application. Background Technology

[0002] After more than a decade of development, lithium-ion batteries have reached a bottleneck in energy density improvement. The main issue is that the lithium storage capacity of commercially available positive and negative electrode materials has essentially reached its theoretical limit. Graphite-carbon anode materials have reached a capacity of 360 mAh / g, close to the theoretical value of 372 mAh / g, leaving very little room for further improvement. To achieve higher energy densities, silicon-based materials, with a theoretical specific capacity as high as 4200 mAh / g, have attracted widespread attention. Compared to graphite materials, silicon-based materials have a theoretical energy density more than 10 times higher and are considered one of the most promising materials for high-capacity anode materials in lithium-ion batteries.

[0003] The main problem with silicon anode materials is their large expansion rate, which can reach 300%. This significant expansion rate ultimately leads to the pulverization of the active material and the destruction of the SEI film on the electrode surface during application, resulting in poor cycle performance. Simultaneously, due to silicon's semiconductor properties, its conductivity is also poor, manifesting as poor rate performance. Therefore, silicon anode materials still face significant challenges for practical applications in lithium-ion batteries. Summary of the Invention

[0004] To overcome the technical problems of large volume variation of silicon-based anode materials, particle pulverization of silicon materials, and repeated growth of surface SEI film in existing technologies, this invention provides a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure and its preparation method.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] The first aspect of the present invention provides a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure. The silicon-carbon composite material is composed of a three-dimensional network structure composed of nano-silicon and carbon and a carbon coating layer disposed outside the three-dimensional network structure. The three-dimensional network structure has a carbon structure as a skeleton, and the nano-silicon is uniformly embedded on the carbon skeleton.

[0007] The specific surface area of ​​the three-dimensional network structure is 9–12 m². 2 / g, the specific surface area of ​​the silicon-carbon composite material is less than 5m². 2 / g.

[0008] The silicon-carbon composite material of this invention has a three-dimensional network carbon structure, exhibiting good electronic conductivity. Silicon particles are uniformly embedded on the surface of the carbon skeleton or completely embedded within it, facilitating electron migration and interconduction in any direction within the three-dimensional space. Furthermore, the aforementioned three-dimensional network carbon structure provides an elastic carrier for the silicon embedded in the carbon skeleton, suppressing the massive volume expansion of silicon during charging and discharging, preventing silicon particle breakage, and reducing the expansion and contraction effects of the silicon-carbon composite material throughout the three-dimensional space. Ultimately, this network structure results in a silicon-carbon composite material with superior performance. Simultaneously, coating the three-dimensional structure with a carbon layer further reduces the specific surface area of ​​the material from approximately 10 μm before coating, making the silicon surrounded by carbon. 2 / g decreased to 5m 2 Below / g, the material becomes denser, improving conductivity while also reducing side reactions.

[0009] As an optional implementation, in the silicon-carbon composite material provided by the present invention, the thickness of the coated carbon layer is 1 to 10 nm, and the particle size of the silicon-carbon composite material is 5 to 20 μm.

[0010] The second invention provides a method for preparing silicon-carbon composite materials based on a three-dimensional network silicon-carbon structure, comprising the following steps:

[0011] S1. After uniformly mixing nano-silicon and high-volatile organic carbon source, isostatic pressing is performed to obtain an isostatic block. The pressure of the isostatic pressing is 50-300 MPa and the processing time is 60-90 min.

[0012] S2. Break the isostatic block obtained in step S1.

[0013] S3. The crushed particles obtained in step S2 are subjected to a first sintering treatment under the protection of an inert gas to obtain original particles with a three-dimensional network structure. The first sintering process includes three heating stages: the first heating stage is 100-300℃; the second heating stage is 600-800℃; and the third heating stage is 1000-1200℃.

[0014] S4. After crushing the raw particles obtained in step S3, sieve them to obtain raw powder.

[0015] S5. After the original powder obtained in step S4 is mixed evenly with the carbon coating agent, a second sintering is carried out under the protection of inert gas. The second sintered material is crushed and sieved to obtain a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure.

[0016] In this invention, isostatic pressing is used to tightly bond silicon and carbon, ensuring they remain connected before sintering and preventing them from loosening during the sintering process. During sintering, volatiles in the high-volatile organic carbon source evaporate, forming a silicon-carbon three-dimensional network structure after sintering. Then, carbon is coated onto the outside of the three-dimensional network structure to further reduce the specific surface area of ​​the material and improve its conductivity.

[0017] In the sintering process of this invention, the first rapid heating is to accelerate the volatilization of low-boiling-point volatiles (water vapor, short-chain hydrocarbons, and other organic gases), and the designed temperature holding is to ensure that the volatilization reaction is complete at this temperature; the second rapid heating is to accelerate the volatilization of medium- and high-boiling-point volatiles (medium- and long-chain hydrocarbons, benzene rings, and other organic gases), and the designed temperature holding is also to ensure that the volatilization reaction is complete at this temperature; the first two rapid heatings are for the carbon network structure formed during the complete volatilization process of the volatiles; the third slow heating is high-temperature carbonization, where the organic volatiles have been completely volatilized, and only a small amount of CO2 gas is volatilized, and slow heating is to stabilize the formed carbon network structure.

[0018] As an optional implementation, in the preparation method provided by the present invention, the high volatile organic carbon source is selected from one or more of low-temperature softening point asphalt, thermoplastic resin, and tar.

[0019] In this invention, mild softening point asphalt, thermoplastic resin, and tar are selected as high volatile organic carbon sources. During the carbonization process, a large amount of gas escapes, which can form a large number of internal pores. Furthermore, due to the large amount of gas, the internal pores can be opened up, which is conducive to the formation of a three-dimensional network structure.

[0020] As an optional implementation method, in the preparation method provided by the present invention, the particle size D50 of the high volatile organic carbon source is 2-10 μm.

[0021] The particle size D50 of organic carbon sources is 2-10 μm. In principle, smaller particle size is more conducive to dispersion with silicon. However, smaller particles are more difficult to process. Therefore, the particle size is limited to within 10 micrometers, which is conducive to dispersion and easy to process.

[0022] As an optional implementation, in the preparation method provided by the present invention, the nano-silicon includes one or more of metallic silicon, solar polycrystalline silicon, chemical vapor deposition silicon, and physical vapor deposition silicon, and the particle size D50 of the nano-silicon is 20-100 nm.

[0023] By limiting the particle size of nano-silicon to 20–100 nm, including both nano-silicon prepared by grinding and nano-silicon prepared by vapor deposition, the functions described in this application can be achieved.

[0024] As an optional implementation, in the preparation method provided by the present invention, the mass ratio of nano-silicon to high-volatile organic carbon source in step S1 is (0.7-1):(1.5-3.0).

[0025] In this invention, if the mass ratio of nano-silicon to high-volatile organic carbon source exceeds the above range, it will affect the specific capacity of the material. As the silicon ratio increases, the specific capacity of the material will increase.

[0026] As an optional implementation, in the preparation method provided by the present invention, the particle size of the crushed particles in step S1 is 3-10 mm.

[0027] As an optional implementation, in the preparation method provided by the present invention, in step S3, the heating rate in the first heating stage is 3-7℃ / min, and the holding time is 60-120min; the heating rate in the second heating stage is 8-12℃ / min, and the holding time is 60-120min; the heating rate in the third heating stage is 0.5-1.5℃ / min, and the holding time is 60-120min.

[0028] As an optional implementation method, in the preparation method provided by the present invention, nitrogen or inert gas is first introduced before heating in step S3, and the temperature is raised three times and then naturally cooled to room temperature, with nitrogen gas introduced for protection throughout the process.

[0029] As an optional implementation, in the preparation method provided by the present invention, the amount of carbon coating agent added in step S5 is 1-10% of the original powder mass, so that the thickness of the carbon coating layer is controlled between 1-10 nm.

[0030] As an optional implementation, in the preparation method provided by the present invention, the carbon coating agent in step S5 is asphalt.

[0031] As an optional implementation, in the preparation method provided by the present invention, the carbon coating agent is selected from one of high-temperature softening point asphalt, medium-temperature softening point asphalt, and low-temperature softening point asphalt.

[0032] As an optional implementation, in the preparation method provided by the present invention, the carbon coating agent is selected from high-temperature softening point asphalt, with a ring and globe softening point of 200-300℃ and a particle size D50 of 2-10μm.

[0033] In this invention, a carbon coating agent is added and sintered with the original powder to fill and coat the surface of the original powder, thereby reducing the specific surface area of ​​the material.

[0034] As an optional implementation, in the preparation method provided by the present invention, the second sintering in step S5 includes two heating stages: the first heating stage is 200-400°C, and the second heating stage is 800-1000°C.

[0035] In this invention, during the second sintering process, the first heating and holding process involves thermally melting the coating agent to form a fluid coating on the silicon carbide structure; the second heating and holding process involves coking and carbonizing the coating agent to form a coke structure.

[0036] As an optional implementation method, in the preparation method provided by the present invention, nitrogen or inert gas is first introduced before heating in step S5. The heating rate in the first stage is 3-7℃ / min, and the temperature is held for 30-120min. The heating rate in the second stage is 3-7℃ / min, and the temperature is held for 60-120min. Then, the temperature is naturally cooled to room temperature, and nitrogen is introduced for protection throughout the process.

[0037] As an optional implementation, in the preparation method provided by the present invention, in step S1, nano-silicon and a high-volatile organic carbon source are mixed uniformly under inert protective gas and constant temperature conditions using a high-speed dispersion device.

[0038] The third aspect of the present invention provides the application of the silicon-carbon composite material based on the above-described three-dimensional network silicon-carbon structure or the silicon-carbon composite material prepared by the above-described method for preparing the silicon-carbon composite material based on the three-dimensional network silicon-carbon structure in lithium-ion batteries.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The three-dimensional network carbon structure in this invention has good electronic conductivity, which is beneficial for the formation of electron migration and mutual conduction in any direction in three-dimensional space for silicon particles embedded in the carbon skeleton. At the same time, the three-dimensional network carbon structure can provide an elastic carrier for silicon embedded in the carbon skeleton, suppressing the huge volume expansion of silicon during charging and discharging, and reducing the expansion and contraction effect of silicon-carbon composite material in the entire three-dimensional space. Ultimately, the silicon-carbon composite material based on this network structure has superior performance. After the three-dimensional structure is coated with a carbon layer, the specific surface area of ​​the material is further reduced, the conductivity is improved, and side reactions are also reduced.

[0041] (2) The preparation method of silicon-carbon composite material provided by the present invention mainly includes isostatic pressing, a first sintering, and a second sintering. The isostatic pressing process ensures that silicon and carbon are tightly bonded, preventing loosening during sintering. After the first sintering, a three-dimensional carbon network structure with silicon embedded in the carbon skeleton is formed. However, the surface of the three-dimensional carbon network structure formed at this time has defects, resulting in an excessively large specific surface area of ​​the material. Therefore, carbon coating is performed through the second sintering to fill and encapsulate the surface of the material, thereby reducing the specific surface area of ​​the material. The process of the present invention is simple, the equipment is highly mature, and it is suitable for large-scale production. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 Figure A is a schematic diagram of the three-dimensional network carbon-silicon structure in this invention. Figure B is a schematic diagram of the original material structure obtained by preparation.

[0044] Figure 2 Electron micrograph of the original material of the three-dimensional network silicon-carbon structure prepared in Example 1;

[0045] Figure 3 for Figure 2 Enlarged image;

[0046] Figure 4 The image shows an electron microscope image of the silicon-carbon composite material with a three-dimensional network carbon-silicon structure prepared in Example 1. Detailed Implementation

[0047] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0049] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0050] I. Preparation of a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure

[0051] Example 1

[0052] A method for preparing silicon-carbon composite materials based on a three-dimensional network silicon-carbon structure includes the following steps:

[0053] (1) Raw material mixing: Take a certain amount of chemical vapor deposition nano-silicon powder (D50≈80nm) and asphalt powder (PE150 asphalt, coking value of about 45%, D50≈5μm) and mix them physically; the mass ratio of nano-silicon powder to asphalt powder is 1:2; use a high-speed dispersion device (model VCH-5L), under nitrogen protection, mix at a dispersion rate of 500rpm for 20min, and then mix at a dispersion rate of 1000rpm for 30min; at the same time, the circulating cooling water is turned on throughout the process; after the raw material mixing is completed, seal and store it in PE bags.

[0054] (2) Isostatic pressing: Fill the powder from step (1) into a silicone soft mold, then vacuum seal it with a PE bag, and put the sealed mold into the isostatic pressing chamber (ultra-high pressure equipment model 600MPa-5L). The isostatic pressing parameters are: pressure 200MPa, holding time 60min. After the pressing is completed, tear off the PE bag and take out the block material from the mold to obtain the isostatic pressing block material.

[0055] (3) Crushing: The isostatic compressed material from step (2) is crushed using a small jaw crusher (model PE100*125), which can be crushed multiple times until the particle size is controlled below 10mm.

[0056] (4) Sintering: The crushed material from step (3) is sintered at high temperature. The temperature control of the tubular furnace is as follows: first, nitrogen or other inert gas is purged for 30 minutes at a rate of 1.5 L / min; then, the temperature is raised from room temperature to 150°C at a rate of 5°C / min and held for 120 minutes; then, the temperature is raised to 700°C at a rate of 10°C / min and held for 120 minutes; then, the temperature is raised to 1100°C at a rate of 1°C / min and held for 120 minutes; finally, the temperature is naturally cooled to room temperature, with nitrogen purging as a protective gas throughout the process at a rate of 1.0 L / min. This yields the original material with a three-dimensional network silicon-carbon structure. See Figure 2 and Figure 3 .

[0057] (5) Crushing: Take out the sintered material after high-temperature carbonization and grind and crush it. The crushed material passes through a 325-mesh standard sieve and the particle size D50 is controlled between 5 and 20 μm to obtain the original powder.

[0058] (6) Secondary mixing of carbon coating agent: Physically mix the original powder and carbon coating agent powder (high temperature asphalt MQ280, ring and ball softening point 280℃) from step (5); the amount of carbon coating agent added is 5% of the mass of the original powder; use a high-speed dispersion device (model VCH-5L), under nitrogen protection, mix at a dispersion rate of 500 rpm for 20 min; mix at a dispersion rate of 1000 rpm for 30 min; at the same time, the circulating cooling water is turned on throughout the process; after the material powder is mixed, it is sealed and stored in a PE bag.

[0059] (7) Secondary sintering: The mixed powder in step (6) is subjected to secondary sintering treatment. The temperature control of the tube furnace is as follows: first, nitrogen or other inert gas is purged for 30 min at a rate of 1.0 L / min; then, the temperature is raised from room temperature to 300℃ at a rate of 5℃ / min and held for 120 min; then, the temperature is raised to 1000℃ at a rate of 5℃ / min and held for 120 min; then, the temperature is naturally cooled to room temperature, with nitrogen purged as a protective gas throughout the process at a rate of 0.5 L / min.

[0060] (8) Crushing: The secondary sintered material obtained in step (7) is crushed and passed through a 325-mesh sieve. The particle size D50 is controlled at 15.0±5.0um, thus obtaining a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure. See Figure 4 .

[0061] The obtained silicon-carbon composite material was named A1.

[0062] Example 2

[0063] A method for preparing a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure differs from Example 1 in that:

[0064] In step (1), the PE150 asphalt powder was replaced with PE100 asphalt powder (PE100 asphalt, coking value 42%, D50≈5μm); in step (2), the hydrostatic treatment pressure was 100MPa and the holding time was 80min; all other steps were the same as in Example 1. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure was named A2.

[0065] Example 3

[0066] A method for preparing a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure differs from Example 1 in that:

[0067] In step (1), the asphalt PE150 powder was replaced with phenolic resin powder (phenolic resin 2123, coking value 38%, D50≈8μm), and in step (6), the amount of carbon coating agent added was 2% of the original powder mass. All other steps were the same as in Example 1. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure was named A3.

[0068] Example 4

[0069] A method for preparing a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure differs from Example 1 in that:

[0070] In step (1), the asphalt PE150 powder was replaced with polyacrylonitrile (PAN) powder (PAN powder, coking value 44%, D50≈10μm). In step (6), the amount of carbon coating agent added was 10% of the original powder mass. All other steps were the same as in Example 1. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure was named A4.

[0071] Example 5

[0072] A method for preparing a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure differs from Example 1 in that:

[0073] In step (1), the chemical vapor deposition nano-silicon powder was replaced with physical vapor deposition nano-silicon powder (D50≈75nm), and the mass ratio of nano-silicon powder to asphalt powder was 1:3; in step (2), the hydrostatic treatment pressure was 50MPa, and the holding time was 90min; all other steps were the same as in Example 1. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure was named A5.

[0074] Comparative Example 1

[0075] A method for preparing a silicon-carbon composite material differs from that in Example 1 in that:

[0076] Excluding the isostatic pressing process in step (2) and the crushing process in step (3), all other steps are the same as in Example 1. The resulting powder material is a primary material with a silicon-carbon dispersed structure (without a three-dimensional network silicon-carbon structure), named B1.

[0077] Comparative Example 2

[0078] A method for preparing a silicon-carbon composite material differs from that in Example 1 in that:

[0079] Excluding step (6) secondary carbon coating agent mixing, step (7) secondary sintering, and step (8) pulverization, all other steps are the same as in Example 1. The resulting powder material is a primary material with a three-dimensional network structure of carbon silicon, named B2.

[0080] Comparative Example 3

[0081] A method for preparing a silicon-carbon composite material differs from that in Example 1 in that:

[0082] Excluding the isostatic pressing process in step (2) and the crushing process in step (3), excluding the secondary carbon coating agent mixing in step (6), the secondary sintering process in step (7), and the pulverizing process in step (8), all other steps are the same as in Example 1. The resulting powder material is a primary material with a silicon-carbon dispersed structure (without a three-dimensional network silicon-carbon structure), named B3.

[0083] II. Fabrication of Button Electrodes

[0084] Electrode fabrication: The negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-3 were respectively mixed with conductive agent SP, binder LA133 and deionized water in a certain proportion to form a uniform slurry, wherein the mass ratio of silicon-carbon negative electrode material: conductive agent SP: binder LA133 was 50:30:20; the homogenization equipment was a vacuum degassing machine with a speed of 2000 rpm and a time of 10 min.

[0085] The prepared slurry is evenly coated on copper foil and then placed in a 100℃ forced-air drying oven for drying. The baked electrode is cut and pressed into a circular electrode of a certain size. After being accurately weighed (accurate to 0.0001g), it is placed in a vacuum drying oven and baked at 120℃ for 8 hours under vacuum conditions to obtain a button electrode.

[0086] The button cell assembled from material A1 is denoted as A1 button cell, and so on, resulting in button cells A1, A2, A3, A4, A5 and B1, B2, B3.

[0087] III. Performance Testing

[0088] 1. Performance testing of silicon-carbon composite materials based on three-dimensional network silicon-carbon structure.

[0089] The schematic diagrams of the original carbon-silicon structure material prepared in Example 1 and the silicon-carbon composite material obtained after carbon coating are shown below. Figure 1 As shown, the silicon-carbon composite material consists of a three-dimensional network structure composed of nano-silicon and carbon. The nano-silicon is uniformly embedded in the carbon skeleton, and the white particles represent silicon, which is either embedded on the surface of the carbon skeleton or completely embedded within it. The three-dimensional network structure is externally coated with a carbon layer. Scanning electron microscopy (SEM) was used to examine the material, and the results are shown below. Figure 2-4 As shown, where Figure 2 The original material for the three-dimensional network silicon-carbon structure obtained through a single sintering process. Figure 3 for Figure 2 The magnified image shows that the small white particles are nano-silicon (including...). Figure 2 and Figure 3 (As indicated by the middle arrow), the gray area represents carbon, forming a porous three-dimensional network structure. Figure 4 To obtain the final silicon-carbon composite material, from Figure 4 It can be seen that the silicon-carbon composite material is coated with a dense carbon layer. Electron microscopy analysis showed that the specific surface area of ​​the original silicon-carbon structure material prepared in Example 1 was approximately 10 m². 2 / g, the final composite material has a specific surface area of ​​approximately 5m². 2 / g, the material is more compact.

[0090] 2. Performance testing of button electrodes

[0091] The assembled batteries were subjected to open-circuit voltage testing. Batteries with an open-circuit voltage above 2.0V were selected for 0.1C first charge-discharge efficiency and reversible capacity testing. The electrical performance comparison of several batteries is shown in Table 1.

[0092] Table 1: Electrical performance of button cells

[0093]

[0094]

[0095] In lithium-ion battery applications, silicon-based anode materials suffer from significant volume changes, silicon particle pulverization, and repeated growth of the SEI film, leading to increased irreversible lithium consumption and a relative decrease in reversible lithium. This directly impacts battery performance, resulting in high lithium intercalation capacity but relatively low reversible lithium extraction capacity, leading to low initial charge-discharge efficiency. As shown in the table above, the three-dimensional network carbon-silicon structure constructed in this invention effectively mitigates the volume expansion of silicon-based anode materials in three-dimensional space. The carbon chains embedded in the nano-silicon within the network structure prevent silicon particle breakage, and the carbon chains also increase the electrical conductivity between silicon particles. Compared to silicon-carbon composites without a three-dimensional network silicon-carbon structure (such as B1 in the table), the electrical performance of this composite material (such as B2 in the table) is significantly improved. Furthermore, by secondary coating the original particles with a three-dimensional network silicon-carbon structure, the specific surface area of ​​the material is further reduced, increasing conductivity while also reducing side reactions. For example, A1-A5 have higher reversible capacity and initial efficiency compared to B2. In B3, the composite material lacks both a three-dimensional network structure and carbon coating, resulting in lower lithium intercalation capacity, reversible capacity, and initial efficiency compared to A1-A5. The silicon-carbon composite material based on a three-dimensional network silicon-carbon structure ultimately prepared by this invention possesses competitive electrical performance in the field of lithium-ion battery anode applications.

[0096] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing silicon-carbon composite materials based on a three-dimensional network silicon-carbon structure, characterized in that, Includes the following steps: S1. After uniformly mixing nano-silicon and high-volatile organic carbon source, isostatic pressing is performed to obtain an isostatic block. The pressure of the isostatic pressing is 50~300MPa and the processing time is 60~90min. S2. Break the isostatically compressed block obtained in step S1; S3. The crushed particles obtained in step S2 are subjected to a first sintering treatment under the protection of an inert gas to obtain original particles with a three-dimensional network structure; the first sintering process includes three heating stages, the first heating stage being 100~300℃. The second heating stage is 600~800℃; the third heating stage is 1000~1200℃; the heating rate of the first heating stage is 3~7℃ / min, and the holding time is 60~120min; the heating rate of the second heating stage is 8~12℃ / min, and the holding time is 60~120min. The heating rate in the third heating stage is 0.5~1.5℃ / min, and the holding time is 60~120min; S4. After crushing the raw particles obtained in step S3, sieve them to obtain raw powder; S5. After the original powder obtained in step S4 is mixed evenly with the carbon coating agent, it is sintered for the second time under the protection of inert gas. The sintered material is crushed and sieved to obtain silicon-carbon composite material based on three-dimensional network carbon-silicon structure. The silicon-carbon composite material consists of a three-dimensional network structure composed of nano-silicon and carbon, and a carbon coating layer disposed on the outside of the three-dimensional network structure. The three-dimensional network structure uses carbon as a skeleton, and the nano-silicon is uniformly embedded on the carbon skeleton.

2. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The specific surface area of ​​the three-dimensional network structure is 9~12m². 2 / g, the specific surface area of ​​the silicon-carbon composite material is less than 5m². 2 / g.

3. The method for preparing a silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The thickness of the carbon coating layer is 1~10nm, and the particle size of the silicon-carbon composite material is 5~20μm.

4. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The high volatile organic carbon source is selected from one or more of low-temperature softening point asphalt, thermoplastic resin, and tar, and the particle size D50 of the high volatile organic carbon source is 2~10μm.

5. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, In step S1, the mass ratio of nano-silicon to high-volatile organic carbon source is (0.7~1):(1.5~3.0).

6. The method for preparing silicon-carbon composite materials based on a three-dimensional network silicon-carbon structure according to any one of claims 1-5, characterized in that, In step S3, nitrogen or an inert gas is first introduced before heating, and the temperature is raised three times before being naturally cooled to room temperature. Nitrogen gas is introduced for protection throughout the process.

7. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The amount of carbon coating agent added in step S5 is 1 to 10% of the original powder mass.

8. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The carbon coating agent is selected from one of the following: high-temperature softening point asphalt, medium-temperature softening point asphalt, and low-temperature softening point asphalt.

9. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The carbon coating agent is selected from high-temperature softening point asphalt, with a ring and globe softening point of 200~300℃ and a particle size D50 of 2~10μm.

10. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, The second sintering in step S5 includes two heating stages: the first heating stage is 200~400℃ and the second heating stage is 800~1000℃.

11. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 10, characterized in that, Before heating in step S5, nitrogen or inert gas is first introduced. The heating rate in the first heating stage is 3~7℃ / min, and the temperature is held for 30~120min. The heating rate in the second heating stage is 3~7℃ / min, and the temperature is held for 60~120min. Then, the temperature is naturally cooled to room temperature, and nitrogen is introduced for protection throughout the process.

12. The method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to claim 1, characterized in that, In step S1, nano-silicon and high-volatile organic carbon source are mixed evenly using a high-speed dispersion device under inert protective gas and constant temperature conditions.

13. The application of the silicon-carbon composite material prepared by the method for preparing silicon-carbon composite material based on a three-dimensional network silicon-carbon structure according to any one of claims 1-12 in lithium-ion batteries.

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