Carbon source mixed gas CVD coated silicon-carbon negative electrode material and preparation method and lithium ion battery

Abstract

The present invention relates to the field of lithium-ion battery technology, in particular to a carbon source mixed gas CVD-coated silicon-carbon negative electrode material and preparation method and a lithium-ion battery. The preparation method comprises the following steps: 1) preparation of the silicon-carbon material: placing porous carbon in an apparatus, regulating the gas velocity and the dynamic rotation rate of the apparatus to uniformly disperse it, raising the temperature to 380-650°C, and introducing a silane mixed gas with a concentration of 5-50% to form the silicon-carbon material; 2) mixed gas carbon-coated silicon-carbon material: introducing mixed gas sources of different proportions into the apparatus, regulating the gas velocity and the dynamic rotation rate of the apparatus to uniformly disperse it, raising the temperature to 450-700°C, and achieving uniform carbon coating on the surface of the silicon-carbon material. The present invention solves the explosion problem caused by a single acetylene self-polymerization reaction; moreover, the uniform carbon coating isolates the side reaction problem caused by direct contact between the electrolyte and nano-silicon, thereby improving the stability of the silicon-carbon material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically relates to a carbon source mixed gas CVD-coated silicon-carbon negative electrode material, a preparation method, and a lithium-ion battery. Background Art

[0002] The rapid development of new energy vehicles is placing higher demands on the energy density and rate performance of lithium-ion batteries. New silicon-carbon materials are attracting widespread attention as the most promising anode materials for the next generation of lithium-ion batteries. Silicon, as a lithium-ion battery anode material, offers advantages such as low cost, high capacity, and a low discharge plateau. However, it also presents challenges such as volume expansion during charge and discharge, leading to material failure, low conductivity, and low initial coulombic efficiency. The silicon-carbon anode, formed by combining nano-sized silicon with carbon, significantly reduces silicon expansion and improves conductivity, providing an effective approach to addressing these issues.

[0003] Existing methods for coating silicon-carbon materials present numerous challenges. For example, the high coating temperatures of single carbon source gases like methane, ethylene, and propylene lead to significant capacity degradation and fail to meet the commercial silicon-carbon requirements for low surface area and zero gas production. Furthermore, the acetylene-carbon coating process, which has a relatively low cracking temperature, is highly susceptible to explosion hazards due to its self-polymerization reaction under high temperature and pressure, posing a significant safety hazard to industrial production.

[0004] Therefore, there is an urgent need in this field to develop a safe, stable, simple process and uniform surface coating carbon source mixed gas CVD coated silicon-carbon negative electrode material preparation method. Summary of the Invention

[0005] The object of the present invention is to provide a silicon-carbon negative electrode material and a preparation method and a lithium-ion battery using a variety of carbon source mixed gas CVD coating at a relatively low temperature. The carbon-coated silicon-carbon negative electrode material prepared by the present invention has a narrow overall particle size distribution and has the characteristics that the particle size and capacity can be adjusted according to demand. The carbon layer of the silicon-carbon negative electrode material coated with the obtained carbon source mixed gas is dense and uniform, so the low resistivity, low specific surface area and high silicon content effectively maintain the high capacity, cycle and rate performance of the battery. On the one hand, the capacity attenuation caused by high-temperature coating of methane, ethylene and propylene and the explosion problem caused by acetylene self-polymerization reaction are solved. On the other hand, the uniform carbon coating layer isolates the side reaction problem caused by direct contact between the electrolyte and nano-silicon, thereby improving the stability of the silicon-carbon material.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material comprises the following steps:

[0008] (1) Preparation of silicon-carbon material: Porous carbon is placed in the equipment, the gas velocity and the dynamic rotation rate of the equipment are adjusted to make it uniformly dispersed, the temperature is raised to 380-650°C, and a silane mixture with a concentration of 5-50% is introduced, and the silicon is deposited by gas phase decomposition to form silicon-carbon material;

[0009] (2) Mixed gas carbon coating of silicon-carbon materials: introduce mixed gas sources of different proportions into the equipment, adjust the gas velocity and the dynamic rotation rate of the equipment to make it evenly dispersed, and heat it to 450-700℃ to achieve uniform carbon coating on the surface of the silicon-carbon material.

[0010] Further, any one of the following three preparation methods is adopted:

[0011] The first preparation method:

[0012] (1) Preparation of silicon-carbon material: porous carbon is placed in a fluidized bed, the stirring rate is adjusted to 10-80 r / min, the fluidizing gas velocity is adjusted to 0.01-0.1 m / s, and the bed is uniformly fluidized. The bed is heated to 380-650°C, and a silane mixture with a concentration of 5-50% is introduced to obtain a silicon-carbon material with a silicon content of 30-80%.

[0013] (2) Mixed gas carbon coating of silicon-carbon materials: introduce mixed gas sources of different proportions into the fluidized bed, adjust the stirring rate to 10-80 r / min, the fluidizing gas velocity to 0.01-0.1 m / s, raise the temperature to 450-700℃, and the reaction time to 1-10h to achieve uniform carbon coating on the surface of the silicon-carbon material.

[0014] The second preparation method:

[0015] (1) Preparation of silicon-carbon material: Place porous carbon in a converter, adjust the rotation speed to 5-40 r / min, introduce a gas velocity of 0.01-0.05 m / s, mix the materials evenly, raise the temperature to 380-650°C, introduce a silane mixture with a concentration of 5-50% to form a silicon-carbon material;

[0016] (2) Mixed gas carbon coating of silicon-carbon materials: introduce mixed gas sources of different proportions into the converter, adjust the rotation speed to 5-40 r / min, the gas velocity to 0.01-0.05 m / s, and raise the temperature to 450-700°C to achieve uniform carbon coating on the surface of the silicon-carbon material.

[0017] The third preparation method:

[0018] (1) Preparation of silicon-carbon material: porous carbon is spread in a fixed bed, the gas velocity is 0.01-0.05 m / s, the temperature is raised to 380-650°C, and a silane mixture with a concentration of 5-50% is introduced to form a silicon-carbon material;

[0019] (2) Mixed gas carbon coating of silicon-carbon materials: Mixed gas sources of different proportions are introduced into the fixed bed at a gas velocity of 0.01-0.05 m / s, and the temperature is raised to 450-700°C to achieve uniform carbon coating on the surface of the silicon-carbon material.

[0020] The porous carbon precursor may be one or more of coconut shell carbon, wood carbon, fruit shell carbon, petroleum coke, phenolic carbon, asphalt carbon, starch carbon, and glucose carbon.

[0021] The D50 particle size of the porous carbon is 3-25 μm, such as 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, and 20 μm (the particle size mentioned here is the average particle size). Preferably, the D50 particle size is 7-20 μm.

[0022] Among them, the pore volume of porous carbon is 0.4-1.5 cm 3 / g, such as 0.5 cm 3 / g, 0.55 cm 3 / g, 0.6 cm 3 / g, 0.65cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4cm 3 / g, 1.5 cm 3 / g. Preferably 0.5-1.0 cm 3 / g.

[0023] Among them, porous carbon BET is 500-2900 m 2 / g, such as 500 m 2 / g, 600 m 2 / g, 700 m 2 / g, 800 m 2 / g, 1100 m 2 / g, 1500 m 2 / g, 1800 m 2 / g, 2100 m 2 / g, 2500 m 2 / g, 2900 m 2 / g. Preferably 600-2900 m 2 / g.

[0024] The silane mixed gas is one or more of silane+nitrogen, silane+argon, or silane+helium. The silane concentration of the silane mixed gas may be 5%, 10%, 20%, 30%, 40%, or 50%.

[0025] The silicon deposition amount is 20-80%, preferably 25-70%.

[0026] The carbon coating mixed gas source includes a shielding gas, silane, and a carbon source gas, and the mixing mass ratio is 1:(0.1-1):(0.1-5). The mass ratio of shielding gas to silane can be 1:0.1, 1:0.15, 1:0.2, 1:0.3, 1:0.5, 1:1, 1:2, 1:3, 1:4, etc. The mass ratio of silane to carbon source gas can be 0.1:0.1, 0.1:0.3, 0.1:0.4, 0.1:0.5, 0.1:0.6, 0.1:0.7, 0.1:0.8, 0.1:0.9, 0.1:1, or 0.2:0.1, etc.

[0027] The protective gas is at least one of nitrogen, argon, helium and hydrogen;

[0028] The silane includes (SiH4)monosilane, (Si2H6)disilane or (Si n H 2n+2 ) higher order silicon hydride compounds, where n is a positive integer.

[0029] The carbon source gas includes at least one of methane, ethane, ethylene, acetylene, propylene, propane, n-butene, isobutylene, butadiene, n-butane, isobutane, carbon monoxide, or carbon dioxide. When two carbon source gases are used, their mass ratio can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0030] Wherein, the carbon coating temperature is 450-700°C, for example, 450°C, 470°C, 490°C, 510°C, 530°C, 550°C, 570°C, 590°C, 610°C, 630°C, 650°C, 670°C, 690°C, etc., and more preferably 450-650°C.

[0031] Wherein, the coating time is 0.5-12h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, more preferably 1-10h, and the coating time can be further adjusted according to the requirements of carbon coating quality.

[0032] Wherein, based on the mass of the silicon-carbon material as 100%, the mass of the carbon coating in the carbon-coated silicon-carbon negative electrode material is 0.5%-12%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11% or 12%, and more preferably 1%-10%. If the relative amount of carbon coating is too low, the thickness of the coating layer will be thin and the coating uniformity will be poor; and if the relative amount of carbon coating is too high, the battery capacity will be reduced and the preparation cost will increase.

[0033] A lithium-ion battery is provided, which adopts the carbon source mixed gas CVD-coated silicon-carbon negative electrode material prepared by the above preparation method.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The preparation process of the carbon source mixed gas CVD coated silicon-carbon negative electrode material of the present invention is simple, and the subsequent silicon deposition and carbon coating steps can be completed by adding materials once, and the discharge is uniform without powder agglomeration and agglomeration. At the same time, the dust pollution problem caused by the intermittent steps is avoided, which meets the needs of large-scale production.

[0036] (2) The carbon coating method using carbon source mixed gas can prevent nano-silicon from directly contacting the air, effectively reduce the surface activity of silicon-carbon negative electrode materials, and greatly improve the safety of the production process.

[0037] (3) The silicon-carbon negative electrode material prepared by the coating method of the present invention has the characteristics of low resistivity, low specific surface area, high silicon content, and amorphous silicon structure, which ensures the overall conductivity, electron transfer rate and energy density of the electrode material.

[0038] (4) The silicon-carbon negative electrode material prepared by low-temperature coating with a carbon source mixture solves the problems of capacity decay and explosion caused by acetylene self-polymerization caused by high-temperature coating with methane, ethane, ethylene, and propylene. On the other hand, the uniform carbon coating isolates the side reactions caused by direct contact between the electrolyte and nano-silicon, thereby improving the stability of the silicon-carbon material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope photograph of the carbon source mixed gas CVD-coated silicon-carbon negative electrode material prepared in Example 1.

[0040] Figure 2 This is a cycle test diagram of a lithium-ion battery using the carbon source mixed gas CVD coating of the silicon-carbon negative electrode material in Example 1.

[0041] Figure 3This is a scanning electron microscope photograph of the carbon source mixed gas CVD-coated silicon-carbon negative electrode material prepared in Example 2.

[0042] Figure 4 This is a lithium-ion battery cycle test diagram using the carbon source mixed gas CVD coating of the silicon-carbon negative electrode material in Example 2.

[0043] Figure 5 The results of the soft pack cycle performance test are shown in Figure 2.

[0044] Figure 6 Surface activity test results.

[0045] Figure 7 This is the XRD test result. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 are within the scope of protection of the present invention.

[0047] Example 1

[0048] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a fluidized bed), specifically comprising the following steps:

[0049] (1) Set the pore volume to 0.5 cm 3 / g, BET is 500m 2 / g, coconut shell charcoal with a particle size of D50 = 3μm was placed in a fluidized bed, the stirring rate was regulated to 10 r / min, the fluidizing gas velocity was 0.01 m / s to make it uniformly fluidized, the temperature was raised to 380℃, and a silane mixture with a concentration of 5% was introduced to obtain a silicon-carbon material with a silicon content of 50%.

[0050] (2) Argon, monosilane, and carbon source gas (the mass ratio of propylene and butene is 1:1) are mixed in a mass ratio of 1:0.1:0.1 and introduced into the fluidized bed of step (1). The stirring rate is regulated to 10 r / min, the fluidizing gas velocity is 0.01 m / s, the temperature is raised to 450°C, the reaction time is 1 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixture coating amount of 10%.

[0051] Scanning electron microscope photos of carbon source mixed gas CVD coated silicon carbon negative electrode material Figure 1 As shown in the figure, the lithium ion battery cycle test using the carbon source mixed gas CVD coated silicon carbon negative electrode material is as follows Figure 2 shown.

[0052] Example 2

[0053] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a fluidized bed), specifically comprising the following steps:

[0054] (1) Set the pore volume to 1.0 cm 3 / g, BET is 2900m 2 / g, fruit shell carbon with a particle size of D50=7μm was placed in a fluidized bed, the stirring rate was regulated to 80 r / min, the fluidizing gas velocity was 0.1 m / s to make it uniformly fluidized, the temperature was raised to 450℃, and a silane mixture with a concentration of 50% was introduced to obtain a silicon-carbon material with a silicon content of 60%.

[0055] (2) Argon, monosilane, and carbon source gas (the mass ratio of propylene and butene is 1:1) are mixed in a mass ratio of 1:0.1:5 and introduced into the fluidized bed of step (1). The stirring rate is regulated to 80 r / min, the fluidizing gas velocity is 0.1 m / s, the temperature is raised to 600°C, the reaction time is 3 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixture coating amount of 1%.

[0056] Scanning electron microscope photos of carbon source mixed gas CVD coated silicon carbon negative electrode material Figure 3 As shown in the figure, the lithium ion battery cycle test using the carbon source mixed gas CVD coated silicon carbon negative electrode material is as follows Figure 4 shown.

[0057] Example 3

[0058] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a converter), specifically comprising the following steps:

[0059] (1) Set the pore volume to 0.5 cm 3 / g, BET is 500m 2 / g, wood carbon with a particle size of D50=3μm is placed in a converter, the rotation speed is adjusted to 10 r / min, the temperature is raised to 380℃, and a silane mixture with a concentration of 5% is introduced to obtain a silicon-carbon material with a silicon content of 30%.

[0060] (2) Nitrogen, monosilane, and carbon source gas (the mass ratio of propylene and butadiene is 1:1) are mixed in a mass ratio of 1:0.1:0.1 and introduced into the converter of step (1). The rotation speed is adjusted to 10 r / min, the temperature is raised to 450°C, the reaction time is 5 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixture coating amount of 10%.

[0061] Example 4

[0062] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a converter), specifically comprising the following steps:

[0063] (1) Set the pore volume to 1.0 cm 3 / g, BET is 2900m 2 / g, glucose carbon with a particle size of D50=7μm was placed in a converter, the rotation speed was adjusted to 80 r / min, the temperature was raised to 450℃, and a silane mixture with a concentration of 50% was introduced to obtain a silicon-carbon material with a silicon content of 60%.

[0064] (2) Nitrogen, monosilane, and carbon source gas (the mass ratio of propylene and butadiene is 1:1) are mixed in a mass ratio of 1:0.1:5 and introduced into the converter of step (1). The rotation speed is adjusted to 80 r / min, the temperature is raised to 600°C, the reaction time is 3 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixture coating amount of 1%.

[0065] Example 5

[0066] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a fixed bed), specifically comprising the following steps:

[0067] (1) Set the pore volume to 0.5 cm 3 / g, BET is 500m 2 / g, petroleum coke with a particle size of D50 = 3 μm is evenly spread in a fixed bed, the gas velocity is 0.01 m / s, the temperature is raised to 380°C, and a silane mixture with a concentration of 5% is introduced to obtain a silicon-carbon material with a silicon content of 30%.

[0068] (2) Nitrogen, monosilane, and carbon source gas (the mass ratio of propylene and n-butene is 1:1) are mixed in a mass ratio of 1:0.1:0.1 and introduced into the fixed bed of step (1) at a gas velocity of 0.01 m / s. The temperature is raised to 450°C, the reaction time is 5 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixed gas coating of 10%.

[0069] Example 6

[0070] A method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material (the equipment uses a fixed bed), specifically comprising the following steps:

[0071] (1) Set the pore volume to 1.0 cm 3 / g, BET is 2900m 2 / g, pitch carbon with particle size D50=7μm is evenly spread in a fixed bed, the air velocity is 0.1m / s, the temperature is raised to 450℃, and a silane mixture with a concentration of 50% is introduced to form a silicon-carbon material with a silicon content of 50%.

[0072] (2) Nitrogen, monosilane, and carbon source gas (the mass ratio of propylene and n-butene is 1:1) are mixed in a mass ratio of 1:0.1:5 and introduced into the fixed bed of step (1) at a gas velocity of 0.1 m / s. The temperature is raised to 600°C, the reaction time is 3 h, and the mixture is naturally cooled to room temperature to obtain a silicon-carbon negative electrode material with a carbon source mixed gas coating of 1%.

[0073] Performance testing:

[0074] 1. Pole expansion rate test

[0075] Conventional acetylene-coated and mixed gas-coated silicon-carbon anode materials were coated, and the thickness of the silicon-carbon anode electrode plates after lithium insertion was tested to verify the expansion rate of the silicon-carbon anode. This test was based on a silicon-carbon material with a silicon content of 50%. The preparation steps for the conventional acetylene-coated silicon-carbon anode material were the same as in Example 1, with the only difference being that the mixed gas source in Example 1 was replaced with acetylene. The mixed gas-coated process was performed according to Example 1.

[0076] Test steps:

[0077] (1) After coating the silicon-carbon negative electrode material slurry, measure its thickness and assemble it into a button-type half-cell;

[0078] (2) Discharge and lithium embedding test on the button battery and then disassemble the electrode;

[0079] (3) Re-measure the thickness of the electrode after lithium insertion;

[0080] (4) The difference in thickness between the two measurements is the expansion, and thickness difference / electrode thickness = expansion rate.

[0081] The test results are shown in Tables 1 and 2 below.

[0082] Table 1

[0083]

[0084] Table 2

[0085]

[0086] Test conclusion: By comparing the two sets of expansion rate data, it was found that the average expansion rate of the electrode piece of the silicon-carbon negative electrode material with carbon on the mixed gas source of the present invention after lithium insertion was reduced by 14.3% compared with the silicon-carbon negative electrode material with carbon on acetylene.

[0087] 2. Soft pack cycle performance test

[0088] By compounding with graphite, that is, the addition amount of silicon-carbon negative electrode material is 10% and the addition amount of graphite is 90%, the difference in soft pack cycle performance of the mixed gas source carbon silicon-carbon negative electrode material of Example 1 and the conventional acetylene carbon silicon-carbon negative electrode material at 25°C is compared. The results are as follows Figure 5 shown.

[0089] Test conclusion: By comparison, it is found that the silicon-carbon negative electrode material with carbon on the mixed gas source of the present invention has a lower expansion rate and smaller capacity decay during the cycle.

[0090] 3. Resistivity and specific surface area test

[0091] The resistivity and specific surface area of ​​the silicon-carbon negative electrode material with conventional acetylene carbon with a silicon content of 50% and the mixed gas source carbon in Example 1 were tested respectively. The results are compared in Table 3 below.

[0092] Table 3

[0093]

[0094] Test conclusion: The silicon-carbon negative electrode material after carbonization of the mixed gas source of the present invention has greater advantages in specific surface area and enhanced conductivity.

[0095] 4. Surface activity test

[0096] Using a water + silicon-carbon negative electrode material slurry method, the amount of hydrogen produced is measured at 45°C to describe the strength of the surface activity of the silicon-carbon negative electrode material, that is, the integrity of the carbon coating.

[0097] Steps:

[0098] (1) Use a homogenizer to mix 4g of silicon-carbon material and 10g of water;

[0099] (2) Pour the mixed slurry into an aluminum-plastic bag, seal it, and place the sealed bag in dimethyl silicone oil at 45°C;

[0100] (3) Continuously weigh the weight of the aluminum-plastic bag and convert it into gas production according to the Archimedes principle.

[0101] The results are as follows Figure 6 The results of the 24-hour slurry gas production test showed that the silicon-carbon negative electrode material with carbon on the mixed gas source of the present invention produced less gas, indicating that its surface activity was weaker and the carbon coating was more complete, which could better isolate the side reactions caused by the contact between the internal nano-silicon and the electrolyte, thereby improving the stability of the silicon-carbon negative electrode material.

[0102] 5. XRD test

[0103] The XRD test was performed on the silicon-carbon negative electrode material with carbon on the mixed gas source in Example 1 and the silicon-carbon negative electrode material with carbon on methane. The results are as follows. Figure 7 The steps for preparing the silicon-carbon negative electrode material with carbon on methane are the same as those in Example 1, with the only difference being that the mixed gas source in Example 1 is replaced with methane.

[0104] When methane is used for carbon coating, due to the high temperature at which methane forms cracked carbon, XRD test results show that some silicon carbon forms SiC at high temperatures. However, the theoretical capacity of SiC is lower than that of Si (4200 mAh / g), which leads to capacity decay of the silicon-carbon negative electrode material. Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon source mixed gas CVD coated silicon-carbon negative electrode material, characterized in that: The following steps are involved: (1) Preparation of silicon-carbon material: porous carbon is placed in the equipment, the gas velocity and the dynamic rotation rate of the equipment are adjusted to make it uniformly dispersed, the temperature is raised to 380-650°C, and a silane mixture with a concentration of 5-50% is introduced to form a silicon-carbon material; the D50 particle size of the porous carbon is 3-25 μm; the pore volume of the porous carbon is 0.4-1.5 cm 3 / g; the porous carbon BET is 500-2900m 2 / g; the silane mixture is one or more of silane + nitrogen, silane + argon or silane + helium, and the silicon deposition amount is 20-80%; (2) Mixed gas carbon coating of silicon-carbon material: introduce mixed gas sources of different proportions into the equipment, adjust the gas velocity and the dynamic rotation rate of the equipment to make it evenly dispersed, and heat it to 450°C to achieve uniform carbon coating on the surface of the silicon-carbon material; The mixed gas source includes protective gas, silane and carbon source gas, and the mixing mass ratio is 1:0.1:(0.1-5); the protective gas is at least one of nitrogen, argon, helium and hydrogen; the silane includes monosilane, disilane or Si n H 2n+2 A higher-level silicon hydride compound, wherein n is a positive integer; the carbon source gas is propylene and butene or propylene and butadiene, and the mass ratio of propylene to butene and propylene to butadiene is 1:

1.

2. The method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material according to claim 1, characterized in that: Use any of the following three preparation methods: The first preparation method: (1) Preparation of silicon-carbon material: porous carbon is placed in a fluidized bed, the stirring rate is adjusted to 10-80 r / min, the fluidizing gas velocity is adjusted to 0.01-0.1 m / s, and the bed is uniformly fluidized. The bed is heated to 380-650°C, and a silane mixture with a concentration of 5-50% is introduced to form a silicon-carbon material; (2) Mixed gas carbon coating of silicon-carbon materials: different proportions of mixed gas sources are introduced into the fluidized bed, the stirring rate is adjusted to 10-80 r / min, the fluidizing gas velocity is adjusted to 0.01-0.1 m / s, and the temperature is raised to 450°C to achieve uniform carbon coating on the surface of the silicon-carbon material; The second preparation method: (1) Preparation of silicon-carbon material: porous carbon is placed in a converter, the rotation speed is adjusted to 5-40 r / min, the gas velocity is 0.01-0.05 m / s, the material is evenly mixed, the temperature is raised to 380-650°C, and a silane mixture gas with a concentration of 5-50% is introduced to form a silicon-carbon material; (2) Mixed gas carbon coating of silicon-carbon material: different proportions of mixed gas sources are introduced into the converter, the rotation speed is adjusted to 5-40 r / min, the gas velocity is adjusted to 0.01-0.05 m / s, and the temperature is raised to 450 ° C to achieve uniform carbon coating on the surface of the silicon-carbon material; The third preparation method: (1) Preparation of silicon-carbon material: porous carbon is spread in a fixed bed, a gas velocity of 0.01-0.05 m / s is introduced, the temperature is raised to 380-650°C, and a silane mixture gas with a concentration of 5-50% is introduced to form a silicon-carbon material; (2) Mixed gas carbon coating of silicon-carbon materials: Mixed gas sources of different proportions are introduced into the fixed bed at a gas velocity of 0.01-0.05 m / s, and the temperature is raised to 450°C to achieve uniform carbon coating on the surface of the silicon-carbon material.

3. The method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material according to claim 2, characterized in that: The porous carbon is one or more of coconut shell carbon, wood carbon, fruit shell carbon, petroleum coke, phenolic carbon, asphalt carbon, starch carbon, and glucose carbon.

4. The method for preparing a carbon source mixed gas CVD-coated silicon-carbon negative electrode material according to claim 2, characterized in that: The coating time is 0.5-12h.

5. A carbon source mixed gas CVD coated silicon-carbon negative electrode material, characterized by: The method is prepared according to any one of claims 1 to 4.

6. A lithium-ion battery, characterized in that: A carbon source mixed gas CVD-coated silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 4.

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