Preparation method of silicon-carbon composite material, silicon-carbon composite material and lithium-ion battery

Abstract

The present invention discloses a preparation method of a silicon-carbon composite material, a silicon-carbon composite material and a lithium-ion battery, including preparing a nano-silicon deposited porous carbon composite material, wherein the operation steps of preparing the nano-silicon deposited porous carbon composite material include at least: S11), mixing porous carbon, an organic catalyst and an organic pore-forming agent, reacting at a temperature of 50-100°C for at least 1 hour, and obtaining modified porous carbon after filtering and drying; S12), transferring the modified porous carbon to a reaction chamber, heating to not less than 280°C, introducing silane gas into the inlet of the reaction chamber, exhausting hydrogen through the outlet thereof, and maintaining the pressure in the reaction chamber within a target pressure range, and depositing for at least 30 minutes; S13), obtaining the nano-silicon deposited porous carbon composite material; a lithium-ion battery using the silicon-carbon composite material provided by the present invention has excellent performance such as low expansion and good cycle performance.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery material preparation, and specifically relates to a preparation method of a silicon-carbon composite material and a silicon-carbon composite material. The invention also relates to a lithium-ion battery using the silicon-carbon composite material. Background Art

[0002] Silicon-carbon materials produced by sand milling have advantages such as high energy density and a wide range of material sources, making them suitable for applications such as high-energy-density lithium-ion batteries. However, due to large expansion upon full charge and poor cycling performance, they are limited to applications in digital devices and power tools. This expansion is primarily due to the large silicon grains, which expand rapidly, and the weak binding force of the outer carbon coating, which in turn limits the expansion of the silicon, resulting in large expansion and poor cycling performance.

[0003] In current technology, reducing the expansion cycle of silicon can be improved from the aspects of silicon grain size and its coating. Specifically, the nano-silicon prepared by the silane cracking method has the advantages of small grains and low expansion. It is mainly obtained by cracking the silane and depositing it in porous carbon under an inert atmosphere to obtain silicon-carbon material. However, this technical solution still has problems such as low deposition efficiency, poor consistency, and the inability of nano-silicon to be completely deposited in the porous carbon, resulting in the agglomeration of silicon grains, and the deposition of silicon on the surface of the porous carbon, resulting in the exposure of silicon, which in turn causes the reaction of silicon with air and its electrolyte to reduce storage performance.

[0004] Therefore, based on the applicant's dedicated research experience in this field, we hope to seek new technical solutions to solve the above technical problems. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for preparing a silicon-carbon composite material, a silicon-carbon composite material and a lithium-ion battery, wherein the lithium-ion battery used has excellent performances such as low expansion and good cycle performance.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A method for preparing a silicon-carbon composite material, comprising preparing a nano-silicon deposited porous carbon composite material, wherein the steps of preparing the nano-silicon deposited porous carbon composite material at least include:

[0008] S11), mixing the porous carbon, the organic catalyst and the organic pore-forming agent and reacting them for at least 1 hour, filtering and drying to obtain the modified porous carbon;

[0009] S12), transferring the modified porous carbon into a reaction chamber, heating it to no less than 280° C., introducing silane gas into the inlet of the reaction chamber, removing hydrogen through the outlet thereof, and maintaining the pressure in the reaction chamber within the target pressure range, and depositing for at least 30 minutes;

[0010] S13), obtaining the nano-silicon deposited porous carbon composite material.

[0011] Preferably, in the step S11), the reaction is carried out at a temperature of 50-100° C.; and / or the mass ratio of the porous carbon, the organic catalyst and the organic pore-forming agent is in the range of 100:1-10:1-10, more preferably 100:1-5:1-5.

[0012] Preferably, in step S11), when mixing the porous carbon, the organic catalyst and the organic pore-forming agent, the porous carbon is first added to the organic solution of the organic catalyst and dispersed uniformly, and then the organic pore-forming agent is added and mixed uniformly.

[0013] Preferably, in step S11), the organic catalyst is one of dibutyltin oxide, monobutyltin oxide, stannous oxalate, organic bismuth bismuth isooctanoate or organic bismuth bismuth neodecanoate, or a mixture of any of them; and / or the organic pore-forming agent is one of polystyrene, polyethylene glycol, polyvinyl chloride, polyformaldehyde, epoxy resin, polyglycolic acid, lignin, cellulose, and hemicellulose, or a mixture of any of them.

[0014] Preferably, in the step S12), before the silane gas is introduced, the reaction chamber is pre-evacuated and then heated to 300-500° C.; the target pressure range is 0.2-0.4 MPa.

[0015] Preferably, the method comprises the following steps:

[0016] S20), transferring the nano-silicon deposited porous carbon composite material obtained in step S13) to a carbonization device, heating it to 80-250°C and spraying an ether carbon source on the nano-silicon deposited porous carbon composite material for at least 1 hour to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and using the amorphous carbon-coated nano-silicon porous carbon composite material as the silicon-carbon composite material.

[0017] Preferably, in the step S20), after vacuuming and heating to 100-200°C, an ether carbon source is sprayed onto the nano-silicon deposited porous carbon composite material; and / or the spraying rate of the ether carbon source is 1-10 ml / min, and the spraying time is 1-6 hours; and / or the ether carbon source is one of methyl ether, ethyl ether, butyl ether, and diphenyl ether, or a mixture of any of them.

[0018] Preferably, a silicon-carbon composite material is obtained by the preparation method of the silicon-carbon composite material as described above.

[0019] Preferably, the silicon-carbon composite material comprises a core and a shell, the core is composed of porous carbon and a metal compound, and the shell is composed of amorphous carbon; wherein the shell accounts for 1-10 wt % of the weight of the silicon-carbon composite material.

[0020] Preferably, a lithium-ion battery includes a battery negative electrode plate, wherein the battery negative electrode plate includes the silicon-carbon composite material as described above.

[0021] The present application uses an organic pore-forming agent to form pores in porous carbon, and the reaction of the pore-forming agent with the porous carbon can enhance the strength of the porous carbon, thereby reducing the expansion of nano-silicon. In addition, the amorphous carbon left after the subsequent carbonization of the pore-forming agent also has a porous structure, which can further increase the deposition amount of nano-silicon. At the same time, an organic catalyst is further introduced in the process of forming pores in the porous carbon. The present application surprisingly found that the organic catalyst can not only achieve a catalytic pore-forming effect, but also the amorphous carbon and its metal elements obtained after catalysis by the organic catalyst can further improve the electronic conductivity of the porous carbon and improve its reaction activity, thereby obtaining a specific nano-silicon deposited porous carbon composite material with excellent performance, which solves the problems of high expansion and poor circulation that are common in existing silicon-carbon composite materials.

[0022] The present application further proposes the use of ether carbon sources to perform external carbon deposition on specific nano-silicon deposited porous carbon composite materials, utilizing the advantages of ether itself such as low boiling point and low carbonization temperature to reduce the grain growth rate of silicon and thus avoid problems such as large expansion caused by excessive silicon grain size. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a SEM image of the silicon-carbon composite material prepared in Example 1 of the present invention;

[0024] Figure 2 It is a flowchart of the steps for preparing the silicon-carbon composite material according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] See Figure 2 As shown, this embodiment provides a method for preparing a silicon-carbon composite material, including preparing a nano-silicon deposited porous carbon composite material, wherein the steps of preparing the nano-silicon deposited porous carbon composite material at least include:

[0026] S11), the porous carbon, the organic catalyst and the organic pore-forming agent are mixed and reacted for at least 1 hour (preferably at a temperature of 50-100°C for 1-6 hours), and the modified porous carbon is obtained after filtration and drying; preferably, in this step S11), the mass ratio of the porous carbon, the organic catalyst and the organic pore-forming agent is in the range of 100:1-10:1-10, more preferably 100:1-5:1-5; when mixing the porous carbon, the organic catalyst and the organic pore-forming agent, the porous carbon is first added to the organic solution of the organic catalyst and dispersed evenly, and then the organic pore-forming agent is added and mixed evenly; the organic catalyst is one or a mixture of any of dibutyltin oxide, monobutyltin oxide, stannous oxalate, organic bismuth bismuth isooctanoate or organic bismuth bismuth neodecanoate; and / or the organic pore-forming agent is one or a mixture of any of polystyrene, polyethylene glycol, polyvinyl chloride, polyformaldehyde, epoxy resin, polyglycolic acid, lignin, cellulose, and hemicellulose.

[0027] S12), transfer the modified porous carbon to the reaction chamber, heat it to not less than 280°C, introduce silane gas into the inlet of the reaction chamber, remove hydrogen through its outlet, and maintain the pressure in the reaction chamber to the target pressure range (preferably 0.2-0.4 MPa), and deposit for at least 30 minutes, preferably 30-300 minutes; preferably, in this step S12), before introducing the silane gas, pre-evacuate the reaction chamber, preferably evacuate to 0.1 Torr or less, and then heat it to 300-500°C, and then introduce silane gas into the inlet of the reaction chamber.

[0028] S13), obtaining a nano-silicon deposited porous carbon composite material.

[0029] Preferably, this embodiment further includes performing amorphous carbon coating on the nano-silicon deposited porous carbon composite material, which specifically includes the following steps:

[0030] S20), transfer the nano-silicon deposited porous carbon composite material obtained in step S13) to a carbonization device, heat it to 80-250°C, spray an ether carbon source on the nano-silicon deposited porous carbon composite material, and evacuate (preferably, evacuate and heat it to 100-200°C before spraying the ether carbon source on the nano-silicon deposited porous carbon composite material, more preferably, evacuate to -0.1Mpa or below); the spraying time is at least 1 hour to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and the amorphous carbon-coated nano-silicon porous carbon composite material is used as a silicon-carbon composite material; preferably, in this step S20), the spraying rate of the ether carbon source is 1-10ml / min, and the spraying time is 1-6 hours; and / or the ether carbon source is one of methyl ether, ethyl ether, butyl ether, and diphenyl ether, or a mixture of any of them.

[0031] Preferably, this embodiment also proposes a silicon-carbon composite material, which is obtained by the preparation method of the silicon-carbon composite material as described in the embodiment above; preferably, in this embodiment, the silicon-carbon composite material includes a core and a shell, the core is composed of porous carbon and a metal compound, and the shell is composed of amorphous carbon; wherein the shell accounts for 1-10wt% of the weight of the silicon-carbon composite material, more preferably 1-8wt%, and further preferably 1-5wt%.

[0032] Preferably, this embodiment also proposes a lithium-ion battery, including a battery negative electrode plate, wherein the battery negative electrode plate includes the silicon-carbon composite material as described above in this embodiment; those skilled in the art can carry out specific applications according to actual needs during implementation, and the specific application method should belong to the conventional technical means of those skilled in the art, so this embodiment does not impose any special and unique restrictions on its application method.

[0033] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0034] Based on the above-described embodiments, the present application further proposes the following specific embodiments:

[0035] Example 1: In this example 1, a silicon-carbon composite material was prepared according to the following steps:

[0036] Step S10) preparing a nano-silicon deposited porous carbon composite material; the specific operation steps of this step S10) are as follows:

[0037] S11), first, 100 g of porous carbon (known porous carbon purchased directly from the market) was added to 300 g of a 1 wt% dibutyltin oxide cyclohexane organic solution and dispersed evenly, and then 3 g of polystyrene was added and mixed evenly; the mixture was reacted at a temperature of 80° C. for 3 hours, filtered, and vacuum-dried at a temperature of 80° C. for 24 hours to obtain a modified porous carbon;

[0038] S12), transferring the modified porous carbon into a reaction chamber, evacuating the reaction chamber to 0.1 Torr in advance, heating it to 400°C, introducing silane SiH4 gas into the inlet of the reaction chamber, excluding hydrogen through its outlet, and maintaining the pressure in the reaction chamber at 0.3 MPa for deposition for 120 minutes;

[0039] S13), obtaining a nano-silicon deposited porous carbon composite material.

[0040] S20) Transfer the nano-silicon deposited porous carbon composite material obtained in step S13) to a tubular furnace (as a carbonization device), evacuate the tubular furnace to -0.1 MPa, heat it to 150°C, and spray methyl ether carbon source onto the nano-silicon deposited porous carbon composite material, wherein the spraying rate is 5 ml / min and the spraying time is 3 hours to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and use the amorphous carbon-coated nano-silicon porous carbon composite material as the silicon-carbon composite material of this embodiment 1.

[0041] The silicon-carbon composite material in Example 1 includes a core and a shell, wherein the core is composed of porous carbon and a metal compound, and the shell is composed of amorphous carbon; wherein the shell accounts for approximately 2.5 wt % of the weight of the silicon-carbon composite material.

[0042] The present application conducted a SEM (scanning electron microscope) morphology test on the silicon-carbon composite material obtained in Example 1, and the test results are as follows: Figure 1 As shown, we pass Figure 1 It can be seen that the particle size of the silicon-carbon composite material is 5-15 μm.

[0043] Example 2: In this example 2, a silicon-carbon composite material was prepared according to the following steps:

[0044] Step S10) preparing a nano-silicon deposited porous carbon composite material; the specific operation steps of this step S10) are as follows:

[0045] S11), first, 100 g of porous carbon (known porous carbon purchased directly from the market) was added to 100 g of a 1 wt% monobutyltin oxide cyclohexane organic solution and uniformly dispersed, and then 1 g of polyethylene glycol was added and mixed uniformly; the mixture was reacted at a temperature of 50° C. for 6 hours, filtered, and vacuum-dried at a temperature of 80° C. for 24 hours to obtain a modified porous carbon;

[0046] S12), transferring the modified porous carbon into a reaction chamber, evacuating the reaction chamber to 0.1 Torr in advance, heating it to 300°C, introducing silane SiH4 gas into the inlet of the reaction chamber, excluding hydrogen through its outlet, and maintaining the pressure in the reaction chamber at 0.2 MPa for deposition for 30 minutes;

[0047] S13), obtaining a nano-silicon deposited porous carbon composite material.

[0048] S20) Transfer the nano-silicon deposited porous carbon composite material obtained in step S13) to a tubular furnace (as a carbonization device), evacuate the tubular furnace to -0.1Mpa, heat it to 100°C, and spray ether carbon source onto the nano-silicon deposited porous carbon composite material, wherein the spraying rate is 1ml / min and the spraying time is 6 hours to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and use the amorphous carbon-coated nano-silicon porous carbon composite material as the silicon-carbon composite material of this embodiment 2.

[0049] Example 3: In this Example 3, a silicon-carbon composite material was prepared according to the following steps:

[0050] Step S10) preparing a nano-silicon deposited porous carbon composite material; the specific operation steps of this step S10) are as follows:

[0051] S11), first, 100 g of porous carbon (known porous carbon purchased directly from the market) was added to 100 g of a 5 wt% stannous oxalate cyclohexane organic solution and uniformly dispersed, and then 5 g of polyvinyl chloride was added and mixed uniformly; the mixture was reacted at a temperature of 100° C. for 1 hour, filtered, and vacuum dried at a temperature of 80° C. for 24 hours to obtain a modified porous carbon;

[0052] S12), transferring the modified porous carbon into a reaction chamber, evacuating the reaction chamber to 0.1 Torr in advance, heating it to 500° C., introducing silane SiH4 gas into the inlet of the reaction chamber, excluding hydrogen through its outlet, and maintaining the pressure in the reaction chamber at 0.4 MPa for deposition for 300 minutes;

[0053] S13), obtaining a nano-silicon deposited porous carbon composite material.

[0054] S20) Transfer the nano-silicon deposited porous carbon composite material obtained in step S13) to a tubular furnace (as a carbonization device), evacuate the tubular furnace to -0.1 MPa, heat it to 200°C, and spray the nano-silicon deposited porous carbon composite material with butane carbon source at a spraying rate of 10 ml / min and a spraying time of 1 hour to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and use the amorphous carbon-coated nano-silicon porous carbon composite material as the silicon-carbon composite material of Example 3.

[0055] Comparative Example 1: The remaining technical solutions of this comparative example 1 are the same as those of Example 1, except that, in this comparative example 1, step S20 is canceled) and the nano-silicon deposited porous carbon composite material obtained in step S13) of Example 1 is directly used as the silicon-carbon composite material of this comparative example 1.

[0056] Comparative Example 2: The remaining technical solutions of this Comparative Example 2 are the same as those of Example 1, except that, in this Comparative Example 2, step S10) is canceled and step S20) is directly implemented; wherein, in this step S20), the porous carbon in step S11) of Example 1 is used to replace the nano-silicon deposited porous carbon composite material obtained in step S13).

[0057] Comparative Example 3: The remaining technical solutions of this Comparative Example 3 are the same as those of Example 1, except that, in step S11) of this Comparative Example 3, 100 g of porous carbon is added to 300 g of a 1 wt% dibutyltin oxide cyclohexane organic solution and dispersed evenly; the mixture is reacted at 80°C for 3 hours, and the modified porous carbon is obtained after filtration and vacuum drying at 80°C for 24 hours.

[0058] Comparative Example 4: The remaining technical solutions of this comparative example 4 are the same as those of Example 1, except that, in step S11) of this comparative example 4, 100 g of porous carbon is evenly mixed with 3 g of polystyrene and 100 g of cyclohexane organic solvent; the mixture is reacted at a temperature of 80°C for 3 hours, and the modified porous carbon is obtained after filtration and vacuum drying at a temperature of 80°C for 24 hours.

[0059] Comparative Example 5: The remaining technical solutions of this Comparative Example 5 are the same as those of Example 1, except that, in step S20) of this Comparative Example 5, the nano-silicon deposited porous carbon composite material obtained in step S13) is transferred to a tubular furnace (as a carbonization device), the tubular furnace is evacuated to -0.1 MPa, and after heating to 500°C, a methane carbon source is introduced into the nano-silicon deposited porous carbon composite material and deposited for 6 hours to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and the amorphous carbon-coated nano-silicon porous carbon composite material is used as the silicon-carbon composite material of this Comparative Example 5.

[0060] Comparative Example 6: The remaining technical solutions of this Comparative Example 6 are the same as those of Example 1, except that, in this Comparative Example 6, step S10) is canceled and step S20) is directly implemented; wherein, in this step S20), the nano-silicon deposited porous carbon substrate proposed in Example 1 of the prior patent CN114976026A is used to replace the nano-silicon deposited porous carbon composite material obtained in step S13).

[0061] In order to compare and verify the effects of the above examples and comparative examples, the present application subjected the silicon-carbon composite materials obtained in the above examples 1-3 and comparative examples 1-6 to the following physical and chemical tests:

[0062] 1). The powder conductivity, tap density, specific surface area, and particle size D50 of each silicon-carbon composite material obtained in Examples 1-3 and Comparative Examples 1-6 were tested according to the method in the national standard GB / T 38823-2020 "Silicon Carbon". At the same time, the silicon grain size in each silicon-carbon composite material was tested by XRD; the test results are shown in Table 1 below.

[0063] 2). Button battery test:

[0064] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-6 were used as active materials to prepare pole pieces. The specific preparation method was as follows: 9g of active material, 0.5g of conductive agent SP (conductive carbon black), and 0.5g of binder LA133 were added to 220mL of deionized water and stirred evenly to obtain a slurry; the slurry was coated on a copper foil current collector to obtain the pole pieces corresponding to Examples 1-3 and Comparative Examples 1-6. The pole pieces prepared using the silicon-carbon composite materials corresponding to Examples 1-3 and Comparative Examples 1-6 as active materials are labeled A, B, C, D, E, F, G, H, and I, respectively.

[0065] The prepared electrode was then used as the negative electrode of the battery and assembled into a button battery with a lithium sheet (as the counter electrode), an electrolyte and a separator in a glove box with oxygen and water content both below 0.1 ppm; the separator of the button battery was made of Celegard 2400; the electrolyte was a Li PF6 solution with a Li PF6 concentration of 1.2 mol / L, and the solvent used was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a weight ratio of 1:1.

[0066] The button batteries prepared by using the pole pieces A, B, C, D, E, F, G, H, and I as the negative pole pieces of the battery are marked as A-1, B-1, C-1, D-1, E-1, F-1, G-1, H-1, and I-1; the performance of each button battery is then tested using a blue electric tester. The test conditions used are: using a 0.1C rate of charge and discharge, a voltage range of 0.005V to 2V, and stopping after 3 cycles, and then testing its negative pole. The full-charge expansion, rate performance (2C / 0.1C) and cycle performance (0.1C / 0.1C, 100 cycles) of the sheet are tested. The specific test process for full-charge expansion is as follows: the thickness D1 of each negative electrode sheet after rolling is tested, and then the negative electrode sheet of each button battery is dissected when fully charged to 100% SOC, and its full-charge thickness D2 is tested, and then the expansion rate is calculated, expansion rate = (D2-D1) / D1*100%; the test results are shown in Table 1 below.

[0067] Table 1

[0068]

[0069] It can be seen from Table 1 above that the silicon-carbon composite materials provided in Examples 1-3 of the present application have significantly improved powder electrical conductivity compared with Comparative Examples 1-6. The main reason is that a specific modified porous carbon is used to reduce surface defects, making it easier for the nano-silicon obtained by silane cracking to deposit in its pores. At the same time, after the modified porous carbon is doped with metal elements, the nanopore size of the porous carbon is smaller, and the electronic conductivity is improved, making it easier for the nano-silicon to deposit in the pores, while improving the density and tap density of the material. Moreover, since the embodiments of the present application use liquid organic matter (spraying ether carbon source) to deposit amorphous carbon at low temperature, the silicon grains grow less.

[0070] 3).Soft pack battery test:

[0071] The silicon-carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-6 were doped with 90% artificial graphite as negative electrode materials and mixed with positive electrode ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte and diaphragm are assembled into a 5Ah soft-pack battery; wherein, the diaphragm of the soft-pack battery is Celegard 2400, the electrolyte is Li PF6 solution, wherein the solvent of the Li PF6 solution is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of Li PF6 is 1.3 mol / L; the soft-pack batteries prepared from the corresponding silicon-carbon composite materials in Examples 1-3 and Comparative Examples 1-6 are marked as A-2, B-2, C-2, D-2, E-2, F-2, G-2, H-2, and I-2, respectively.

[0072] The following performance tests are performed on each soft pack battery:

[0073] a. After the fixed capacity, each soft pack battery is dissected and its negative electrode sheet thickness D1 is tested. Then each soft pack battery is cycled 100 times (cycle conditions are: 1C / 1C@25±3℃@2.5-4.2V) and then fully charged. Then the negative electrode sheet is dissected again and its thickness D2 is tested. Then the expansion rate is calculated. The expansion rate is The test results are shown in Table 2 below.

[0074] Table 2

[0075]

[0076] It can be seen from Table 2 above that the expansion rate of the negative electrode plate of the soft-pack lithium-ion battery manufactured using the silicon-carbon composite material provided in Examples 1-3 of the present application is significantly lower than that of Comparative Examples 1-6; the main reason for this is that the silicon-carbon composite material provided in the Examples of the present application has the characteristic of small silicon grains, which can significantly reduce expansion.

[0077] b. Perform cycle performance tests and rate tests on each soft-pack battery. The test conditions for the cycle performance test are: a charge and discharge voltage range of 2.5 to 4.2 V, a temperature of 25 ± 3.0 ° C, and a charge and discharge rate of 1.0 C / 1.0 C. The test conditions for the rate test are: testing the constant current ratio of each soft-pack battery under 2 C conditions. The test results are shown in Table 3 below.

[0078] Table 3

[0079]

[0080] It can be seen from Table 3 above that the soft-pack batteries made using the silicon-carbon composite materials provided in Examples 1-3 of the present application perform significantly better than those in Comparative Examples 1-6 in terms of cycle performance and rate performance. The main reason is that the silicon-carbon composite materials provided in the examples of the present application have the advantage of low expansion, which can significantly improve the cycle performance of lithium-ion batteries used therein. Moreover, since the silicon-carbon composite materials provided in the examples of the present application have high powder conductivity, the impedance can be further reduced, thereby significantly improving the fast charging performance (constant current ratio) of the material.

[0081] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0082] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The method comprises preparing a nano-silicon deposited porous carbon composite material, wherein the steps of preparing the nano-silicon deposited porous carbon composite material at least include: S11), mixing the porous carbon, the organic catalyst and the organic pore-forming agent and reacting them for at least 1 hour, filtering and drying to obtain the modified porous carbon; in the step S11), the reaction is carried out at a temperature of 50-100° C.; in the step S11), the organic catalyst is one or a mixture of dibutyltin oxide, monobutyltin oxide, stannous oxalate, organic bismuth bismuth isooctanoate or organic bismuth bismuth neodecanoate; the organic pore-forming agent is one or a mixture of polystyrene, polyethylene glycol, polyvinyl chloride, polyoxymethylene, epoxy resin, polyglycolic acid, lignin, cellulose, hemicellulose; S12), transferring the modified porous carbon into a reaction chamber, heating it to no less than 280° C., introducing silane gas into the inlet of the reaction chamber, exhausting hydrogen through the outlet thereof, and maintaining the pressure in the reaction chamber within the target pressure range, and depositing for at least 30 minutes; S13), obtaining the nano-silicon deposited porous carbon composite material; S20), transferring the nano-silicon deposited porous carbon composite material obtained in step S13) to a carbonization device, heating it to 80-250°C and spraying an ether carbon source on the nano-silicon deposited porous carbon composite material for at least 1 hour to obtain an amorphous carbon-coated nano-silicon porous carbon composite material, and using the amorphous carbon-coated nano-silicon porous carbon composite material as the silicon-carbon composite material.

2. The method for preparing the silicon-carbon composite material according to claim 1, wherein: The mass ratio of the porous carbon, the organic catalyst and the organic pore-forming agent is in the range of 100:1-10:1-10.

3. The method for preparing the silicon-carbon composite material according to claim 2, wherein: The mass ratio of the porous carbon, the organic catalyst and the organic pore-forming agent is in the range of 100:1-5:1-5.

4. The method for preparing the silicon-carbon composite material according to claim 1, wherein: In the step S11), when the porous carbon, the organic catalyst and the organic pore-forming agent are mixed, the porous carbon is first added to the organic solution of the organic catalyst and dispersed uniformly, and then the organic pore-forming agent is added and mixed uniformly.

5. The method for preparing the silicon-carbon composite material according to claim 1, wherein: In the step S12), before the silane gas is introduced, the reaction chamber is pre-evacuated and then heated to 300-500° C.; the target pressure range is 0.2-0.4 MPa.

6. The method for preparing the silicon-carbon composite material according to claim 1, wherein: In the step S20), after vacuuming and heating to 100-200° C., an ether carbon source is sprayed onto the nano-silicon deposited porous carbon composite material; and / or the spraying rate of the ether carbon source is 1-10 ml / min, and the spraying time is 1-6 hours; and / or the ether carbon source is one of methyl ether, ethyl ether, butyl ether, and diphenyl ether, or a mixture of any of them.

7. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material is obtained by the preparation method according to any one of claims 1 to 6.

8. The silicon-carbon composite material according to claim 7, characterized in that: The silicon-carbon composite material includes a core and a shell, wherein the core is composed of porous carbon and a metal compound, and the shell is composed of amorphous carbon; wherein the shell accounts for 1-10 wt % of the weight of the silicon-carbon composite material.

9. A lithium-ion battery comprising a negative electrode plate, characterized in that: The battery negative electrode plate comprises the silicon-carbon composite material as claimed in claim 7 or 8.

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