A method for multi-batch negative pressure deposition of silicon in porous carbon based on staged parameter optimization

Abstract

The application discloses a method for multi-batch negative pressure deposition of silicon in porous carbon based on staged parameter optimization, and relates to the technical field of gas phase deposition on the surface and in the pores of porous materials. The application proposes to adjust the single-batch gas volume, the proportion of inert gas, the pressure and the temperature to control the deposition rate under the condition of negative pressure, and to optimize the input of silane in stages. The process flow is as follows: in the early stage, low gas volume is inputted to dilute the inert gas to delay the blockage of the pore, in the middle stage, the gas volume is increased to accelerate the filling of the inner layer, and in the later stage, the gas volume or the temperature is reduced to avoid over-deposition of the outer surface. The method and the matching system are suitable for the process optimization method for the multi-batch deposition of silicon and oxides of silicon in porous carbon materials under the condition of negative pressure, and the porous carbon materials mainly have micropores and auxiliary mesopores.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous material surface and pore gas deposition, especially to a process for depositing silicon and its oxides in multiple batches under negative pressure conditions on a porous carbon material mainly composed of micropores and supplemented by mesopores, which belongs to the technical field of chemical industry, material preparation and surface modification. BACKGROUND

[0002] Porous carbon has a wide range of applications in energy storage, electrochemistry, and electrocatalysis due to its high specific surface area and hierarchical pore structure. Micropores (<2 nm) in porous carbon can provide a large number of active sites, but excessive deposition in the micropores can hinder the transmission of reaction gas to the interior, thereby affecting uniform pore filling.

[0003] The current common methods of introducing silane mainly include:

[0004] (1) Continuous introduction of silane under positive pressure: maintain a positive pressure higher than atmospheric pressure (e.g., 1-3 bar) in the reaction chamber, introduce a high-speed fluidizing gas flow to suspend the porous carbon particles, and continuously introduce silane at a set temperature until the reaction is complete. No vacuum pumping is performed during the entire process. This method is mainly aimed at uniform deposition on the surface of macroscopic particles in a fluidized state. However, the deposition rate in the micropore inlet is fast, the gas penetration is limited under positive pressure, and a blocking layer is easily formed, leading to insufficient deposition in the internal micropores and mesopores, which is not suitable for obtaining high filling rates for structures mainly composed of micropores and supplemented by mesopores.

[0005] (2) Uniform introduction of silane under negative pressure: divide the total amount of silane gas into several batches, and pump the vacuum to 0.01-1.0 torr after each batch reaction to remove residual gas and byproducts before introducing the next batch. This method can alleviate micropore blockage and improve filling uniformity, but the batch gas amount is fixed, the initial blockage is still significant, and the total number of batches is large. SUMMARY

[0006] The present application provides a method for multi-batch negative pressure deposition of silicon in porous carbon based on staged parameter optimization, which adjusts the single batch gas amount, inert gas proportion, pressure and temperature to control the deposition rate according to the deposition process. The process flow mainly includes:

[0007] (1) Early stage: low gas amount and inert gas dilution to delay pore blockage.

[0008] (2) Middle stage: increase the gas amount to accelerate the filling of the inner layer.

[0009] (3) Late stage: reduce the gas amount or temperature to avoid over-deposition on the outer surface.

[0010] Each batch reaction is followed by vacuum pumping to 0.01-1.0 torr before introducing the next batch, maintaining consistent reaction conditions, and improving deep penetration effect.

[0011] The present application adopts a negative pressure deposition technology combined with a parameter optimization model to gradually adjust relevant parameters (such as bias, gas flow, temperature, etc.) in each deposition period to adapt to changes in deposition conditions, maintain uniformity and improve gas utilization, thereby achieving optimal balance of product performance in a multi-batch manufacturing process. The problems of serious micropore blockage, insufficient internal deposition or multiple batches exist in the continuous gas inlet of the positive pressure fluidized bed and the uniform batch inlet of the negative pressure.

[0012] The present application is a method for multi-batch negative pressure deposition of silicon in porous carbon based on staged parameter optimization, comprising the following steps:

[0013] S1. Place the porous carbon material in a vacuum reaction chamber, vacuumize to 0.01-0.05 torr, and heat to 60-90% of the target deposition temperature;

[0014] S2. Perform three-stage multi-batch deposition of Si by passing in a mixed gas containing silane under negative pressure, set the amount of substance of silane passed in each batch and the total amount of silane passed in each stage according to the stage, the mixed gas passed in each batch also contains inert gas, the mass of inert gas passed in each batch is half of that of silane, heat and maintain pressure, and vacuumize to the initial pressure of 0.01-0.05 torr after each batch reaction is completed;

[0015] S3. Terminate the deposition when the total amount of silane is set to be passed in;

[0016] The target deposition temperature is 400-600℃;

[0017] The micropores in the porous carbon material account for ≥80% of the total pore volume; the mesopores account for ≤20% of the total pore volume; the total mass of silane passed in is 98%-102% of the mass of the porous carbon material; the three stages include an early stage, a middle stage and a late stage, the pressure in the reaction chamber after cracking of the mixed gas passed in each batch in the early stage is not more than 0.5 atm, the mass of silane passed in the early stage is not more than 20% of the total mass of silane, the pressure in the reaction chamber after cracking of the mixed gas passed in each batch in the middle stage is not more than 1.5 atm, the mass of silane passed in the middle stage is 70-90% of the total mass of silane, the pressure in the reaction chamber after cracking of the mixed gas passed in each batch in the late stage is not more than 3.0 atm, and the mass of silane passed in the late stage is 5-10% of the total mass of silane.

[0018] Further, after passing in the mixed gas in each batch in the three stages, maintain the pressure for 1 minute.

[0019] Further, the mass of silane passed in each batch in the early stage is not more than 3.97 mol, the mass of silane passed in each batch in the middle stage is not more than 11.92 mol, and the mass of silane passed in each batch in the late stage is not more than 23.84 mol.

[0020] Further, the mass of the silane introduced in the middle stage of the three stages is 5% to 20% of the total mass of the silane.

[0021] Preferably, the mass of the silane introduced in the middle stage of the three stages is 8% of the total mass of the silane, the mass of the silane introduced in the middle stage is 82.1% of the total mass of the silane, and the mass of the silane introduced in the later stage is 9.9% of the total mass of the silane.

[0022] Preferably, the mass of the silane introduced in the middle stage of the three stages is 20% of the total mass of the silane, the mass of the silane introduced in the middle stage is 70.1% of the total mass of the silane, and the mass of the silane introduced in the later stage is 9.9% of the total mass of the silane.

[0023] Preferably, the mass of the silane introduced in the middle stage of the three stages is 3.36% of the total mass of the silane, the mass of the silane introduced in the middle stage is 86.55% of the total mass of the silane, and the mass of the silane introduced in the later stage is 10.09% of the total mass of the silane.

[0024] Further, the micropore size of the porous carbon material is < 2 nm; and the pore size distribution range of the mesopore is 2-50 nm.

[0025] Further, the specific surface area of the porous carbon material is 1000-2000 m 2 / g, preferably 1500 m 2 / g.

[0026] The step S3 further includes forming a carbon layer on the Si surface of the porous carbon material.

[0027] The coating uses a carbon source, a reaction precursor of a metal oxide, and a promoter as raw materials, the raw materials are introduced into a reactor through a carrier gas, and a floating catalyst chemical vapor deposition method is used to form a carbon layer on the Si surface of the porous carbon material, the promoter is selected from one or both of thiophene and sulfur, the reaction precursor of the metal oxide is selected from a metallocene of a metal in a metal oxide, and the carbon source includes a gaseous carbon source. The gaseous carbon source includes a hydrocarbon, and the carrier gas includes hydrogen or an inert gas.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) Compared with continuous gas feeding under positive pressure and uniform batch gas feeding under negative pressure, the present application can significantly improve the filling rate of micropores and mesopores by negative pressure driving and adding stages of gas feeding to delay plugging.

[0030] (2) The process parameters in the present application can be quickly predicted through a model, reducing trial and error. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1(a), (b), (c) in FIG. 1 are scanning electron microscope images of the surface of the spherical porous carbon on which a slight excess of silicon was deposited at different magnifications when the silicon was continuously introduced under negative pressure in Comparative Example 1. Figure 1 (d), (e) in FIG. 1 are scanning electron microscope images of the surface of the blocky porous carbon on which a slight excess of silicon was deposited at different magnifications when the silicon was continuously introduced under negative pressure in Comparative Example 1.

[0032] (a), (b) in FIG. 2 are scanning electron microscope images of the surface of the spherical porous carbon on which an excess of silicon was deposited at different magnifications when the silicon was continuously introduced under positive pressure in Comparative Example 2. Figure 2 (c), (d) in FIG. 2 are scanning electron microscope images of the surface of the blocky porous carbon on which an excess of silicon was deposited at different magnifications when the silicon was continuously introduced under positive pressure in Comparative Example 2.

[0033] Figure 3 are scanning electron microscope images of the surface of the blocky porous carbon on which an excess of silicon was deposited at different magnifications when the silicon was introduced in batches under negative pressure in Comparative Example 3.

[0034] Figure 4 are scanning electron microscope images of the surface of the blocky porous carbon on which an excess of silicon was deposited at different magnifications when the silicon was introduced in batches under negative pressure in Comparative Example 3.

[0035] Figure 5 are scanning electron microscope images of the surface of the blocky porous carbon on which an excess of silicon was deposited at different magnifications when the silicon was introduced in batches under negative pressure in Comparative Example 3. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with embodiments. The specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0037] Comparative Example 1: Continuous introduction of silane under negative pressure

[0038] 100 kg of porous carbon material (85 vol % of micropores and 15 vol % of mesopores) was loaded into a closed vacuum reaction chamber with a volume of 1200 L, vacuumed to 0.1 torr (13.4 Pa), and heated to 450°C. 100 kg of silane was uniformly mixed with 50 kg of nitrogen gas, and introduced in batches. Assuming that the silane cracking rate reached 98%, the pressure after each silane reaction could not exceed 150% of atmospheric pressure to prevent the pressure after the next batch of equal amount of silane reaction from being greater than 300% of atmospheric pressure, which would cause the equipment to deform, break or cause a catastrophic leak, leading to spontaneous combustion of silane, and then vacuumed to 0.1 torr.

[0039] Maximum 0.3828 kg (383 g) silane per batch, pressure in the vessel is about 152 kPa or 1140 torr after each cracking:

[0040] Unreacted silane: (1-0.98) x 11.92 = 0.02 x 11.92 = 0.2384 mol;

[0041] Generated hydrogen: 2 x 0.98 x 11.92 = 23.4016 mol;

[0042] Nitrogen: 6.81 mol

[0043] Total moles of gas phase: 0.2384 + 23.4016 + 6.81 = 30.450 mol;

[0044] According to the ideal gas equation, the pressure P = nRT / V = 152569.8 Pa;

[0045] Maximum safe amount of silane per batch: 11.92 mol, maximum safe amount of nitrogen per batch: 6.81 mol.

[0046] Total batches: 261.233, rounded to 262, it takes 6 minutes to complete a cracking reaction and vacuum to the target pressure, and the entire experiment takes about 1572 minutes (26.2 hours).

[0047] From Figure 1 It can be seen that it is easy to cause the phenomenon of blocking the pores of the surface and micropore entrance of the porous carbon, the internal pore channel is insufficiently filled, and the filling uniformity is poor.

[0048] Comparative Example 2: Continuous introduction of silane under positive pressure

[0049] 100 kg of porous carbon material (80 vol% of micropores and 20 vol% of mesopores) is loaded into a fluidized bed reactor with a volume of 1200 L. Inert gas (such as nitrogen or argon) is used to replace the air in the reaction chamber, and preheated to 450°C. Maintain 1.5 atm positive pressure in the reaction chamber, start the fluidization gas flow to make the porous carbon uniformly suspended. Using continuous gas injection, 100 kg of silane gas (3122 mol) and nitrogen are mixed uniformly at a mass ratio of 2:1 and continuously injected into the reaction chamber, keeping the reaction temperature and slight positive pressure constant, and continuing the reaction until all the silane is completely reacted.

[0050] Continuous gas injection, the reaction chamber pressure is constant at 1.5 atm, always within the limit, which can be regarded as "ultra-small batch no continuous batch" - but for ease of comparison, it is equivalent to segmented with a maximum batch size of 11.92 mol / batch.

[0051] Total batch number = 3122 / 11.92 = 262 batches.

[0052] Total reaction time: Actual continuous process, the rate can be approximately considered 2 min per batch, total time = 262 x 2 = 524 min = 8.7 hours.

[0053] As can be seen from Figure 2 , due to the continuous high pressure and high-speed air intake, it is easy to cause rapid deposition on the surface of the porous carbon and the entrance of the micropore, leading to the phenomenon of plugging the hole, insufficient filling of the internal channel, and poor filling uniformity.

[0054] Comparative Example 3: Uniformly batched silane under negative pressure

[0055] 100 kg of porous carbon material (micropores account for 80 vol% of the total pore volume, mesopores account for 20 vol% of the total pore volume) was loaded into a sealed vacuum reaction chamber, vacuumed to 0.05 torr (6.7 Pa), and heated to 450°C. 100 kg of silane was uniformly mixed with 50 kg of nitrogen, and divided into several batches.

[0056] Each batch of silane and nitrogen mixed gas was introduced, and the pressure in the reaction chamber was maintained at about 100 torr (about 0.13 atm). Each batch was allowed to stand for 1 minute, and the vacuum was removed to the initial pressure (6.7 Pa) within 1 minute after the reaction, and the residual gas and by-products were discharged. Repeat the operation until all the silane is introduced, or the target filling rate is reached.

[0057] The maximum safe air intake per batch was 11.92 mol of silane + 6.81 mol of nitrogen. The total number of batches was the same as the positive pressure batch condition: 262 batches. Since the amount of gas removed from 100 torr to the initial pressure is small, the time is short, so the total reaction time is 524 min = 8.7 hours.

[0058] Uniformly batched silane can alleviate the plugging of the hole to some extent and improve the filling uniformity, but since the gas volume per batch is fixed, the risk of initial plugging still exists, and the total number of batches is large, and the operation process is long. As can be seen from Figure 3 , the plugging of the hole at the entrance of the micropore on the surface of the porous carbon material is alleviated.

[0059] Example 1: Three-stage optimized batch injection of silane under negative pressure (pressure ≤ 3 atm)

[0060] 100 kg of porous carbon material (micropores account for 80 vol% of the total pore volume, mesopores account for 20 vol% of the total pore volume) was loaded into a vacuum reaction chamber, vacuumed to 0.05 torr, and heated to 450°C. 100 kg of silane was mixed with nitrogen at a mass ratio of 2:1, and was injected in three stages in batches, and the pressure in the reaction chamber after each batch of cracking was not more than 3 atm (about 303975 Pa);

[0061] (1) According to the pore size distribution and diffusion reaction kinetics, the content of silane in each stage is calculated. If the initial silane concentration is too high, the cracking reaction rate at the pore opening of the porous carbon material will be accelerated, causing the pore opening to be blocked, and the micropore filling needs to meet the "reaction front rate ≤ diffusion rate", otherwise a "shell-hollow core" is formed. In the present application, the range of the amount of silane gas injected in each batch in each stage is set to reserve a buffer to avoid process fluctuations beyond the limit. The amount of silane gas injected needs to be corrected according to the different proportions of micropores and mesopores. In this embodiment, according to the upper limit condition of the reaction chamber pressure after injecting silane cracking in each batch in each stage, and the mass proportion limit of injecting silane in each stage, a target optimization model is established to obtain the number of batches and the total number of batches in each stage;

[0062] The target optimization model includes the following constraints:

[0063] The reaction chamber pressure after cracking in each batch in the early stage is not more than 0.5 atm, corresponding to 3.97 mol of silane injected in each batch;

[0064] The reaction chamber pressure after cracking in each batch in the middle stage is not more than 1.5 atm, corresponding to 11.92 mol of silane injected in each batch;

[0065] The reaction chamber pressure after cracking in each batch in the late stage is not more than 3.0 atm, corresponding to 23.84 mol of silane injected in each batch;

[0066] The reaction time and the time for recovering the initial pressure by vacuum pumping in each batch are 2 min;

[0067]

[0068] x, y, z are the number of batches of silane injected in the early, middle and late stages, respectively, and x, y, z are all greater than 0;

[0069] ; ;

[0070] The target is ;

[0071] The solution that meets the optimization target includes:

[0072] Solution one: x = 15, y = 225, z = 13; 2(x + y + z) = 506 min;

[0073] Solution two: x = 10, y = 228, z = 13; 2(x + y + z) = 502 min;

[0074] Solution three: x = 5, y = 231, z = 13; 2(x + y + z) = 498 min;

[0075] Solution four: x = 5, y = 232, z = 13; 2(x+y+z) = 500 min;

[0076] Solution five: x = 1, y = 235, z = 12; 2(x+y+z) = 496 min;

[0077] Solution six: x = 3, y = 233, z = 13; 2(x+y+z) = 498 min;

[0078] Solution seven: x = 2, y = 233, z = 13; 2(x+y+z) = 496 min;

[0079] Solution eight: x = 1, y = 234, z = 13; 2(x+y+z) = 496 min;

[0080] Solution nine: x = 26, y = 223, z = 13; 2(x+y+z) = 524 min;

[0081] …;

[0082] Solution N-j: x = 63, y = 215, z = 13; 2(x+y+z) = 582 min;

[0083] Solution N: x = 157, y = 183, z = 13; 2(x+y+z) = 706 min;

[0084] A preferred solution is selected from all solutions, such as solution N-j: x = 63, y = 215, z = 13; 2(x+y+z) = 582 min;

[0085] (2) Early stage (about 5-20% batches): 3.97 mol of silane is introduced into each batch, a total of 63 batches (8% batches), each batch of silane and nitrogen is mixed uniformly according to the mass ratio of 2:1, and then introduced into the reaction cavity, the pressure of the reaction cavity is not higher than 0.5 atm, and the pressure is maintained for 1 minute. After each batch reaction, vacuum is extracted to the initial pressure of 0.05 torr to inhibit the clogging of the micropore inlet. In the early stage, 3.97 mol of silane and 2.27 mol of nitrogen are introduced into the reaction cavity for each batch, and the pressure of the reaction cavity after 98% silane cracking is 0.5 atm. Function: low-dose dilution, inhibit rapid deposition of pore mouth.

[0086] (3) Mid-term (about 70~90% batches): 11.92 mol of silane was introduced into each batch, a total of 215 batches (82.1% batches), and the silane was mixed with nitrogen at a mass ratio of 2:1 before being introduced into each batch, the pressure in the reaction chamber was increased to 1.5 atm, and the internal filling was accelerated. In the mid-term stage, 11.92 mol of silane and 6.81 mol of nitrogen were introduced into the reaction chamber for each batch, and the pressure in the reaction chamber after 98% silane cracking was 1.5 atm. Each batch was allowed to react for 1 minute, and the vacuum was drawn to the initial pressure (6.7 Pa) within 1 minute after the reaction. Effect: increase gas volume to accelerate internal filling.

[0087] (4) Late stage (about 5~10% batches): the temperature was reduced by 20℃ to 430℃, 23.84 mol of silane was introduced into each batch, a total of 13 batches (9.9% batches), and the silane was mixed with nitrogen at a mass ratio of 2:1 before being introduced into each batch, the pressure in the reaction chamber was controlled at 3 atm, and the pressure was maintained for 1 minute to prevent over-deposition on the outer surface. In the late stage, 23.84 mol of silane and 13.42 mol of nitrogen were introduced into the reaction chamber for each batch, and the pressure in the reaction chamber after 98% silane cracking was 3 atm. Each batch was allowed to react for 1 minute, and the vacuum was drawn to the initial pressure (6.7 Pa) within 1 minute after the reaction. Effect: prevent over-deposition on the outer surface.

[0088] Throughout the process, the amount of silane and inert gas introduced into each batch was strictly controlled to ensure that the total pressure in the chamber after cracking did not exceed 3 atm, and the vacuum degree reached 1 minute after the reaction.

[0089] Total batch number = 63+ 215+13 =291 batches.

[0090] Total reaction time = 63× 2+215×2+13×2=582 min ≈9.7 hours.

[0091] The comparative effects of the examples and comparative examples are shown in Table 1.

[0092] Table 1

[0093]

[0094] From Figure 4 and Figure 5 It can be seen that the morphology and size of the sample particles, the surface is polyhedral block, the edge is sharp, and there are obvious pores between the particles. And Si is uniformly distributed in the porous carbon, representing higher uniform filling rate of micropores and mesopores, and the pore blocking phenomenon is significantly reduced. Combined with the examples and comparative examples, it can be found that by using three-stage batch injection, the uniform filling rate of micropores and mesopores is higher, and the pore blocking phenomenon is significantly reduced under the condition of little increase in injection reaction time.

[0095] The method for depositing silicon in porous carbon by multiple batches under negative pressure based on staged parameter optimization provided by the application effectively considers internal filling uniformity and pore blocking inhibition, has high deposition efficiency, improves silane utilization rate, optimizes material performance, and is safe and controllable in the whole process.

[0096] Step (4) further includes forming a carbon layer on the Si surface of the porous carbon material.

[0097] The coating process uses a carbon source, a reaction precursor of a metal oxide, and a promoter as raw materials, the raw materials are introduced into a reactor through a carrier gas, and a carbon layer is formed on the Si surface of the porous carbon material by using a floating catalyst chemical vapor deposition method, the promoter is selected from one or both of thiophene and sulfur, the reaction precursor of the metal oxide is selected from a metallocene of a metal in a metal oxide, and the carbon source includes a gaseous carbon source, the gaseous carbon source includes a hydrocarbon such as acetylene, and the carrier gas includes hydrogen or an inert gas.

[0098] Although the above examples have described the application and its implementation in detail, it should be noted that for ordinary skilled persons in the technical field, changes, modifications, substitutions, combinations, simplifications, etc. of corresponding conditions without departing from the technical principles of the application should be regarded as equivalent replacement modes, and these improvements should be regarded as the protection scope of the application.​

Claims

1. A method for multi-batch negative pressure deposition of silicon in porous carbon based on staged parameter optimization, characterized in that, include: S1. Place the porous carbon material in a vacuum reaction chamber, evacuate to 0.01-0.05 torr, and heat to 60-90% of the target deposition temperature; S2. Si is deposited in three stages by introducing a mixed gas containing silane in multiple batches under negative pressure. The amount of silane introduced in each batch and the total amount of silane introduced in each stage are set according to the stages. The mixed gas introduced in each batch also contains an inert gas. The mass of the inert gas introduced in each batch is half that of the silane. The reaction is heated and held under pressure. After each batch of reaction is completed, the vacuum is evacuated to the initial pressure of 0.01-0.05 torr. S3. Deposition is terminated when all silane is introduced; The target deposition temperature is 400-600℃; In the porous carbon material, micropores account for ≥80% of the total pore volume; mesopores account for ≤20% of the total pore volume; and the total mass of silane introduced is 98%~102% of the mass of the porous carbon material. The three stages include an early stage, a middle stage, and a late stage. In the early stage, the pressure in the reaction chamber after each batch of mixed gas is introduced and cracked does not exceed 0.5 atm, and the mass of silane introduced in the early stage is no more than 20% of the total mass of silane. In the middle stage, the pressure in the reaction chamber after each batch of mixed gas is introduced and cracked does not exceed 1.5 atm, and the mass of silane introduced in the middle stage is 70~90% of the total mass of silane. In the late stage, the pressure in the reaction chamber after each batch of mixed gas is introduced and cracked does not exceed 3.0 atm, and the mass of silane introduced in the late stage is 5~10% of the total mass of silane.

2. The method according to claim 1, characterized in that, After each batch of mixed gas is introduced in the three stages, the pressure is maintained for 1 minute.

3. The method according to claim 1, characterized in that, In the early stage, the amount of silane introduced per batch should not exceed 3.97 mol; in the middle stage, the amount of silane introduced per batch should not exceed 11.92 mol; and in the later stage, the amount of silane introduced per batch should not exceed 23.84 mol.

4. The method according to claim 1, characterized in that, In the three stages, the mass of silane introduced in the early stage is 5% to 20% of the total mass of silane.

5. The method according to claim 1, characterized in that, In the three stages, the mass of silane introduced in the early stage is 8% of the total mass of silane, the mass of silane introduced in the middle stage is 82.1% of the total mass of silane, and the mass of silane introduced in the later stage is 9.9% of the total mass of silane.

6. The method according to claim 1, characterized in that, In the three stages, the mass of silane introduced in the early stage is 20% of the total mass of silane, the mass of silane introduced in the middle stage is 70.1% of the total mass of silane, and the mass of silane introduced in the later stage is 9.9% of the total mass of silane.

7. The method according to claim 1, characterized in that, Step S3 is followed by coating the Si surface on the porous carbon material to form a carbon layer.

8. The method according to claim 7, characterized in that, The coating process uses a carbon source, a metal oxide reaction precursor, and a co-catalyst as raw materials. The raw materials are introduced into the reactor via a carrier gas, and a carbon layer is formed on the Si surface of the porous carbon material using a floating catalyst chemical vapor deposition method. The co-catalyst is selected from one or both of thiophene and sulfur. The metal oxide reaction precursor is selected from metal cadmium compounds. The carbon source includes a gaseous carbon source, specifically C. 1-3 The carrier gas is a hydrocarbon, and the carrier gas includes hydrogen or an inert gas.

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