A silicon-carbon negative electrode material and its preparation method and application

Abstract

The present invention discloses a silicon-carbon negative electrode material, a preparation method and an application thereof, wherein the silicon-carbon negative electrode material comprises a substrate and two coating layers coated on the surface of the substrate, the inner coating layer is a carbon coating layer, and the outer coating layer is a high molecular polymer coating layer; the substrate comprises porous carbon and silicon particles. Specifically, a chemical vapor deposition method is adopted to introduce a mixture of silane gas and olefin gas for deposition, so that the silicon particles are smaller than 10nm, which is beneficial to reducing the volume expansion of silicon during the cycle. Then carbon coating is performed, and the first carbon coating preliminarily forms a carbon protective layer on the surface of the substrate to prevent the highly active nano-silicon particles from contacting the air and causing spontaneous combustion or explosion during the cooling and powder removal process. The second carbon coating forms a dense carbon protective layer on the newly exposed carbon substrate surface after crushing and grading and on the surface where the first carbon coating is incomplete. Finally, high molecular polymer coating is performed, so that the high molecular polymer coating layer and the carbon coating layer form a dislocation protection mechanism.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Currently, there are three types of silicon negative electrode materials for lithium batteries: 1. Companies represented by South Korea's Samsung SDI nano-size silicon materials to make silicon nanoparticles, silicon nanowires / tubes, silicon nanofilms and other structures; 2. Companies represented by Japan's Shin-Etsu Chemical and Panasonic use a combination of pre-lithiation silicon oxide and carbon materials to prepare silicon negative electrode materials; 3. Companies represented by China's Shanghai Shanshan and BYD use nano-silicon and carbon material composite technology to prepare silicon-carbon negative electrode materials.

[0003] The silicon negative electrode materials prepared by the above three technical routes can significantly improve the gram capacity of the negative electrode materials, but the large volume expansion of silicon particles during the charging and discharging process will lead to poor cycle performance of the battery cells.

[0004] The patent with publication number CN105680023A discloses a method for preparing a high-rate silicon-based composite material, a negative electrode material, and a lithium battery, and specifically discloses that silicon material is uniformly attached to the inner and outer surfaces of the porous carbon according to a mass ratio; the attached material is subjected to carbon coating treatment to obtain the high-rate silicon-based composite material. Although it uses carbon material to relieve its strain on the one hand and to coat its surface on the other hand to suppress its side reaction with the electrolyte. And the porous structure therein can also better relieve strain and shorten the length of the lithium ion diffusion path. However, its cycle performance only includes 5 and 100 cycles, and more cycles and high-temperature cycles are not clear.

[0005] Patent publication number CN114695865A discloses a silicon anode material, its preparation method, a negative electrode plate, and a lithium-ion battery. Specifically, the silicon anode material comprises a core-shell structure, including a core, an intermediate layer, and an outer shell. The intermediate layer covers at least a portion of the surface of the core, and the outer shell covers at least a portion of the surface of the intermediate layer. The core is a silicon-based material, the intermediate layer is a porous carbon layer, and nano-silicon particles are deposited in at least a portion of the pore structure of the porous carbon layer. Although this silicon anode material employs a core-shell structure comprising a core, an intermediate layer, and an outer shell, the interaction between the layers can both limit the volume expansion of the internal silicon-based material and nano-silicon, thereby increasing battery cycling stability and improving the material's processing performance. The silicon-based material as the core and the nano-silicon increase the overall capacity of the anode material. The use of an ion-conductive polymer as the outer shell for surface coating can mitigate the volume expansion and surface changes of the silicon-based material during charge and discharge. Furthermore, the ion-conductive polymer has good compatibility with the binder, facilitating material processing. However, its cycling performance is limited to 100 and 200 cycles, and high-temperature cycling performance is unclear.

[0006] Patent publication number CN111916745A discloses a silicon negative electrode material, a preparation method thereof, and an electrochemical cell. Specifically, it discloses that in the silicon negative electrode material, the thermosetting polymer is directly formed with the primary silicon particles and the conductive agent without carbonization to form secondary composite particles. The strength and toughness of the thermosetting polymer are utilized to limit the volume of the silicon particles while preventing the secondary composite particles from breaking due to volume changes in the silicon particles. This allows the shape and structure of the secondary composite particles to have better stability and integrity during the charge and discharge cycle, thereby enabling the electrochemical cell to have better electrochemical performance. However, the specific number of cycles and high-temperature cycle performance of the cycle performance are unclear in the performance test of the patent. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a silicon-carbon negative electrode material and its preparation method and application, so as to solve the technical problem that the large volume expansion of silicon particles during the charging and discharging process will lead to poor cycle performance of the battery cell.

[0008] To achieve the above-mentioned objectives, the present invention provides a silicon-carbon negative electrode material, which includes a substrate and two coating layers coated on the surface of the substrate, wherein the inner coating layer is a carbon coating layer and the outer coating layer is a high molecular polymer coating layer; the substrate includes porous carbon and silicon particles.

[0009] Furthermore, the porous carbon is one or more of soft carbon, hard carbon, asphalt-based, etc., with a particle size of 3 to 10 μm and a pore size of 2 to 10 nm.

[0010] Furthermore, the particle size of the silicon particles is less than 10 nm (such as 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm).

[0011] Furthermore, the thickness of the carbon coating layer is 10 to 1000 nm (such as 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm).

[0012] Furthermore, the thickness of the high molecular polymer coating layer is 10 to 1000 nm (such as 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm).

[0013] Furthermore, the polymer used in the polymer coating layer includes one or more of polyolefins, polyesters, polyamides, polyethers, and the like.

[0014] Furthermore, the polyolefins are one or more of polyethylene, polypropylene, polystyrene and polyvinyl chloride.

[0015] Furthermore, the polyester is one or more of polycarbonate and polyterephthalate.

[0016] A method for preparing the above-mentioned silicon-carbon negative electrode material specifically comprises the following steps:

[0017] S1. A mixture of silane gas and olefin gas is deposited on porous carbon, particularly on the pore walls, by chemical vapor deposition to obtain a powder I;

[0018] S2. The mixed gas remaining in the deposition apparatus after deposition is discharged using argon gas, and then one or more gases of methane or acetylene are introduced to the powder I for the first carbon coating, crushing and classifying, and then methane or acetylene gas is introduced for the second carbon coating to obtain powder II;

[0019] S3. Use a spray drying method to evenly coat the polymer on the surface of the powder II to form a continuous, uniform and dense polymer coating layer, thereby obtaining the silicon-carbon negative electrode material.

[0020] Furthermore, in step S1, the porous carbon is one or more of soft carbon, hard carbon, asphalt-based, etc., with a particle size of 3 to 10 μm and a pore size of 2 to 10 nm.

[0021] Furthermore, in step S1, the olefin gas is one or more of ethylene, propylene, etc.

[0022] Furthermore, in step S1, the amount of the olefin gas added is 0.1% to 20% (such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%) of the volume of the silane gas.

[0023] Further, in step S1, the processing temperature of the mixed gas deposition is 600-950°C (such as 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C).

[0024] Furthermore, in step S1, the gas flow rate of the mixed gas deposition is 0.1 to 20 m / s. 3 / min (such as 0.1m 3 / min、0.5m 3 / min、1m 3 / min、2m 3 / min、3m 3 / min、4m 3 / min、5m 3 / min、6m 3 / min、7m 3 / min、8m 3 / min、9m 3 / min、10m 3 / min、11m 3 / min、12m 3 / min、13m 3 / min、14m 3 / min、15m 3 / min、16m 3 / min、17m 3 / min、18m 3 / min、19m 3 / min、20m 3 / min).

[0025] Further, in step S1, the processing time of the mixed gas deposition is 0.5 to 24 hours (such as 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, and 24 hours).

[0026] Furthermore, in step S1 and step S2, a chemical vapor deposition furnace is used for deposition.

[0027] Furthermore, in step S1, the volume of the porous carbon occupies 30% to 85% (such as 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%) of the volume of the furnace chamber of the chemical vapor deposition furnace.

[0028] Further, in step S2, the treatment temperature of the first carbon coating is 600-950°C (such as 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C).

[0029] Furthermore, in step S2, the gas flow rate of the first carbon coating is 0.1 to 20 m 3 / min (such as 0.1m 3 / min、0.5m 3 / min、1m 3 / min、2m 3 / min、3m 3 / min、4m 3 / min、5m 3 / min、6m 3 / min、7m 3 / min、8m 3 / min、9m 3 / min、10m 3 / min、11m 3 / min、12m 3 / min、13m 3 / min、14m 3 / min、15m 3 / min、16m 3 / min、17m 3 / min、18m 3 / min、19m 3 / min、20m 3 / min).

[0030] Furthermore, in step S2, the treatment time of the first carbon coating is 0.5 to 6 hours (such as 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours).

[0031] Furthermore, in step S2, the crushing and classification is performed at room temperature in air.

[0032] Furthermore, in step S2, the particle size range of the particles obtained by the crushing and classification is 2 to 10 μm (such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm).

[0033] Furthermore, in step S2, the treatment temperature of the second carbon coating is 200-1200°C (such as 200°C, 400°C, 600°C, 800°C, 1000°C, 1200°C).

[0034] Furthermore, in step S2, the gas flow rate of the second carbon coating is 0.1 to 20 m 3 / min (such as 0.1m 3 / min、0.5m 3 / min、1m 3 / min、2m 3 / min、3m 3 / min、4m 3 / min、5m 3 / min、6m 3 / min、7m 3 / min、8m3 / min、9m 3 / min、10m 3 / min、11m 3 / min、12m 3 / min、13m 3 / min、14m 3 / min、15m 3 / min、16m 3 / min、17m 3 / min、18m 3 / min、19m 3 / min、20m 3 / min).

[0035] Furthermore, in step S2, the treatment time of the second carbon coating is 0.5 to 24 h (such as 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h).

[0036] Furthermore, in step S3, the spray drying temperature is 200-600°C (such as 200°C, 300°C, 400°C, 500°C, 600°C).

[0037] An application of the above silicon-carbon negative electrode material is to use the silicon-carbon negative electrode material in a lithium-ion battery to improve the energy density of the lithium battery.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The porous carbon structure of the silicon-carbon negative electrode material of the present invention can provide stress buffer space for the expansion of silicon particles and has the function of storing active lithium, which effectively inhibits the expansion of silicon particles and the loss of active lithium during the battery cycle;

[0040] 2. The silicon-carbon negative electrode material of the present invention has silicon particles smaller than 10nm, which is beneficial for reducing silicon volume expansion during the cycle, and the battery cycle performance can be effectively improved by 200-500cls;

[0041] 3. In the silicon-carbon negative electrode material of the present invention, the inner layer of the two coating layers is a continuous, uniform and dense carbon coating layer, which can not only inhibit the splitting and crushing of porous carbon caused by the volume expansion of silicon particles in the late cycle, but also prevent the silicon particles from being directly exposed to the electrolyte, reducing the occurrence of side reactions between the electrolyte and the silicon particles; the outer polymer coating layer can form rich functional groups on the surface of the inner layer, which can form strong hydrogen bonds with the binder having specific functional groups, so that the binder can be firmly attached to the surface of the silicon-carbon negative electrode material. This not only maintains the complete conductive network of the electrode during the cycle, but also promotes the stability of the SEI film, thereby improving the cycle performance of the battery cell;

[0042] 4. The silicon-carbon negative electrode material of the present invention, the polymer coating layer and the carbon coating layer can also form a dislocation protection mechanism, that is, during the battery cycle, the expansion of the silicon particles causes the inner and outer coating layers to rupture to varying degrees and in different regions. The ruptured outer (or inner) layer local area can be protected by the intact inner (or outer) coating layer;

[0043] 5. In the preparation method of the present invention, silane gas is first deposited on porous carbon, particularly in the pore walls, by chemical vapor deposition. During this process, a mixed gas of silane gas and olefin gas is introduced. With the help of olefin gas, the continued growth of silicon particles can be suppressed (the formation of Si-Si bonds can be suppressed). The temperature, gas flow rate, and deposition time of the silicon deposition process are controlled so that the size of the silicon particles deposited on the porous carbon is less than 10 nm. Chemical vapor deposition is more stable than liquid phase deposition, and it is easy to control the reaction speed and has stronger operability (nano-silicon particles are extremely active and are very prone to spontaneous combustion or explosion when exposed to air, water, and water vapor). Then, two carbon coatings are performed. The first carbon coating is to initially form a carbon protective layer on the surface of the substrate to protect the silicon particles and prevent the highly active nano-silicon particles from spontaneous combustion or explosion when contacting air during cooling and removing the powder. The second carbon coating is to form a dense carbon protective layer on the newly exposed substrate surface after crushing and grading and on the surface where the first carbon coating is incomplete. Among them, crushing and grading are carried out between the two carbon coatings because part of the carbon matrix may undergo bonding at high temperature during the chemical vapor deposition process. In addition, the prepared material has specific particle size requirements, so crushing and grading are required. And the temperature of the two carbon coatings can be set according to different scenarios because low-temperature or high-temperature coating will affect the uniformity and integrity of the carbon coating layer. The second carbon coating needs to be reheated. Taking into account energy consumption and coating quality issues, the temperature range is appropriately expanded compared to the first carbon coating temperature range. When the second coating temperature is low, it can achieve energy saving purposes, and when the temperature is high, the quality of the carbon coating layer can be guaranteed. Finally, polymer coating is performed so that the polymer coating layer and the carbon coating layer can form a dislocation protection mechanism, that is, when the inner and outer coating layers are broken to varying degrees and in different regions due to the expansion of silicon particles during the battery cycle, the local area of the broken outer layer (or inner layer) can be protected by a complete inner layer (or outer layer) coating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the structure of the silicon-carbon negative electrode material in Example 1;

[0045] Figure 2 This is a test chart of the high-temperature 45°C cycle capacity retention rate of lithium batteries containing the silicon-carbon negative electrode materials of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0047] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0048] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0049] In the present invention, unless otherwise specified and / or explained, all numerical values involving the amounts of components are "parts by weight". The process parameters in the following examples that are not specified in specific conditions are generally based on conventional conditions.

[0050] Example 1

[0051] A silicon-carbon negative electrode material having a structure as follows Figure 1 As shown, the silicon-carbon negative electrode material includes a substrate and two coating layers coated on the surface of the substrate, wherein the inner coating layer is a carbon coating layer and the outer coating layer is a high molecular polymer coating layer; the substrate includes porous carbon and silicon particles.

[0052] Among them, the porous carbon is hard carbon with a particle size of 5μm and a pore diameter of about 8nm.

[0053] The particle size of the silicon particles is 3 nm.

[0054] The thickness of the carbon coating layer is 100 nm.

[0055] Wherein, the thickness of the high molecular polymer coating layer is 100 nm.

[0056] The polymer used in the polymer coating layer is polyethylene, and the molecular weight of polyethylene is 10 4 -10 6 .

[0057] The preparation method of the above-mentioned silicon-carbon negative electrode material specifically comprises the following steps:

[0058] S1. A mixture of silane gas and olefin gas is deposited on porous carbon, particularly on the pore walls, by chemical vapor deposition to obtain a powder I;

[0059] S2. The mixed gas remaining in the deposition equipment after deposition is discharged using argon gas, and then methane gas is introduced to the powder I for the first carbon coating, crushing and classifying, and then methane or acetylene gas is introduced for the second carbon coating to obtain powder II;

[0060] S3. Use a spray drying method to evenly coat the high molecular weight polymer on the surface of the powder II to form a continuous, uniform and dense high molecular weight polymer coating layer, thereby obtaining a silicon-carbon negative electrode material.

[0061] Among them, the olefin gas is ethylene.

[0062] The amount of olefin gas added is 0.5% of the volume of the silane gas.

[0063] Wherein, in step S1, the processing temperature of the mixed gas deposition is 850°C.

[0064] In step S1, the gas flow rate of the mixed gas deposition is 2m 3 / min.

[0065] In step S1 , the mixed gas deposition process takes 10 hours.

[0066] Wherein, in step S1 and step S2, a chemical vapor deposition furnace is used for deposition.

[0067] Wherein, in step S1 , the volume of the porous carbon occupies 65% of the volume of the furnace chamber of the chemical vapor deposition furnace.

[0068] Wherein, in step S2, the treatment temperature of the first carbon coating is 950°C.

[0069] In step S2, the gas flow rate of the first carbon coating is 3m 3 / min.

[0070] Wherein, in step S2, the first carbon coating treatment time is 4 hours.

[0071] Wherein, in step S2, the crushing and classification are performed at room temperature in air.

[0072] Wherein, in step S2, the particle size of the particles obtained by crushing and classifying is 3 μm.

[0073] Wherein, in step S2, the treatment temperature of the second carbon coating is 850°C.

[0074] Among them, in step S2, the gas flow rate of the second carbon coating is 3m 3 / min.

[0075] Wherein, in step S2, the second carbon coating treatment time is 8 hours.

[0076] Wherein, in step S3, the temperature of spray drying is 350°C.

[0077] The above silicon-carbon negative electrode material is used in a high energy density lithium battery, wherein the high energy density lithium battery is a 5Ah soft pack battery cell. The specific assembly method of the battery cell is as follows:

[0078] The 8 series high Ni-NCM positive electrode material is mixed with superconducting carbon black SuperP, carbon nanotubes and polyvinylidene fluoride in a mass ratio of 96.3:1.0:0.5:2.2, and N-methylpyrrolidone is used as the solvent to prepare the positive electrode slurry. The slurry is coated on a 12μm thick aluminum foil, dried at 85°C, and then compacted at a pressure of 10.0MPa and cut into positive electrode sheets according to certain specifications.

[0079] 95.3 wt% of the negative electrode material prepared in this embodiment, 1.2 wt% of carbon black conductive agent (super-P), 1.5 wt% of carboxymethyl cellulose thickener (CMC), and 2.0 wt% of styrene-butadiene latex binder (SBR) were dissolved in water to prepare a slurry with a solid content of 52%. The slurry was evenly coated on both sides of the copper foil and then rolled, die-cut, and baked to make the negative electrode sheet.

[0080] A polyethylene (PE)-based film of double-sided alumina ceramic is used as the diaphragm, the electrolyte is a 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent is a mixed solution of ethylene carbonate (EC): ethyl carbonate (DMC) with a volume ratio of 1:1. The above-mentioned positive electrode sheets, diaphragms and negative electrode sheets are prepared into soft-pack batteries through a lamination process.

[0081] The lithium battery was tested for cycle capacity retention at 45°C. The test conditions were as follows: test voltage 2.75-4.2V, 0.5C charge, 1C discharge, high temperature 45°C. The test results were as follows: Figure 2 As shown, through Figure 2 It can be seen that the battery cell has good cycle performance, with a capacity retention rate of 80% after 1,600 cycles.

[0082] Comparative Example 1

[0083] A silicon-carbon negative electrode material differs from Example 1 in that it has no carbon coating layer and there is no step S2 in the preparation method, that is, no inner layer coating is used, and the rest of the settings are the same as Example 1.

[0084] The negative electrode material prepared in this comparative example was made into a negative electrode sheet according to the method of Example 1 and assembled into a 5Ah soft pack battery cell. The lithium battery was subjected to a high temperature 45°C cycle capacity retention test. The test conditions were as follows: the test voltage was 2.75-4.2V, 0.5C charge, 1C discharge, and a high temperature of 45°C. The test results are as follows: Figure 2 As shown, through Figure 2It can be seen that the battery cells assembled with only the negative electrode materials prepared by polymer coating have poor cycle performance, and the capacity retention rate drops to 80% after only 700 cycles.

[0085] Comparative Example 2

[0086] A silicon-carbon negative electrode material differs from Example 1 in that it does not have a high molecular polymer coating layer, and there is no step S3 in the preparation method, that is, no outer layer coating is used, and the remaining settings are the same as Example 1.

[0087] The negative electrode material prepared in this comparative example was made into a negative electrode sheet according to the method of Example 1 and assembled into a 5Ah soft pack battery cell. The lithium battery was subjected to a high temperature 45°C cycle capacity retention test. The test conditions were as follows: the test voltage was 2.75-4.2V, 0.5C charge, 1C discharge, and a high temperature of 45°C. The test results are as follows: Figure 2 As shown, through Figure 2 It can be seen that the battery cells assembled with only carbon-coated negative electrode materials have poor cycle performance, with the capacity retention rate dropping to 80% after only 800 cycles.

[0088] Comparative Example 3

[0089] A silicon-carbon negative electrode material is different from Example 1 in that only silane gas is used for vapor deposition in step S1 of the preparation method, and other processes and parameters are the same as those in Example 1.

[0090] The silicon particles in the prepared silicon-carbon negative electrode material had a particle size of 12 nm. The negative electrode material prepared in this comparative example was fabricated into a negative electrode sheet according to the method of Example 1 and assembled into a 5Ah soft-pack battery cell. The lithium battery was subjected to a high-temperature 45°C cycle capacity retention test under the following test conditions: a test voltage of 2.75-4.2 V, a 0.5C charge, a 1C discharge, and a high temperature of 45°C. The test results showed that the capacity retention rate was 80% after 900 cycles.

Claims

1. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material comprises a substrate and two coating layers coated on the surface of the substrate, wherein the inner coating layer is a carbon coating layer and the outer coating layer is a high molecular polymer coating layer; the substrate comprises porous carbon and silicon particles; The porous carbon has a particle size of 3 to 10 μm and a pore size of 2 to 10 nm; The particle size of the silicon particles is less than 10 nm; The method for preparing the silicon-carbon negative electrode material specifically comprises the following steps: S1 using chemical vapor deposition method of a mixture of silane gas and olefin gas is deposited on porous carbon to obtain a powder I; S2. The mixed gas remaining in the deposition equipment after deposition is discharged using argon gas, and then one or more gases of methane or acetylene are introduced to the powder I for the first carbon coating, crushing and classifying, and then methane or acetylene gas is introduced for the second carbon coating to obtain powder II; S3 using a spray drying method to evenly coat the polymer on the surface of the powder II, forming a continuous, uniform and dense polymer coating layer, that is, to obtain the silicon-carbon negative electrode material; In step S1, the amount of the olefin gas added is 0.1% to 20% of the volume of the silane gas.

2. The silicon-carbon negative electrode material according to claim 1, wherein The polymer used in the polymer coating layer includes one or more of polyolefins, polyesters, polyamides, and polyethers.

3. The silicon-carbon negative electrode material according to claim 1, wherein The porous carbon is one or more of soft carbon, hard carbon, and asphalt-based.

4. The silicon-carbon negative electrode material according to claim 1, wherein The thickness of the carbon coating layer is 10-1000 nm.

5. The silicon-carbon negative electrode material according to claim 1, wherein The thickness of the high molecular polymer coating layer is 10-1000 nm.

6. The silicon-carbon negative electrode material according to claim 1, wherein In step S1, the processing temperature of the mixed gas deposition is 600-950°C; the gas flow rate of the mixed gas deposition is 0.1-20 m 3 / min; the processing time of the mixed gas deposition is 0.5~24 h.

7. The silicon-carbon negative electrode material according to claim 1, wherein In step S2, the first carbon coating treatment temperature is 600-950 °C, and the gas flow rate is 0.1-20 m 3 / min, the treatment time is 0.5~6 h; the treatment temperature of the second carbon coating is 200~1200 ℃, the gas flow rate is 0.1~20 m 3 / min, and the processing time is 0.5~24 h.

8. Use of the silicon-carbon negative electrode material according to any one of claims 1 to 7 in a lithium-ion battery.

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