A method for preparing a silicon-carbon material by vapor deposition based on a supercritical carrier gas

Abstract

The application belongs to the field of silicon-carbon negative electrode material manufacturing, and particularly relates to a preparation method of gas deposition silicon-carbon material based on supercritical carrier gas. The method comprises the following steps: vacuum degassing of porous carbon material in a heated state, then introducing silicon-containing gas for silicon deposition with supercritical gas as carrier gas and ultrasonic vibration, repeatedly operating until the required silicon content is reached, and finally introducing carbon source gas for carbon coating to obtain product core-shell structure silicon-carbon composite material. The application realizes uniform deposition of silicon in the porous carbon skeleton through ultrasonic vibration assisted supercritical fluid as carrier gas for silane gas phase deposition, improves the first coulomb efficiency, reduces stress concentration and volume expansion in the charging and discharging process, and improves the cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon anode material manufacturing, specifically relating to a method for preparing silicon-carbon materials by vapor deposition based on supercritical carrier gas. Background Technology

[0002] With the continued growth in demand for high-energy-density batteries from new energy vehicles and portable electronic devices, silicon-based anode material systems, due to their theoretical specific capacity (4200 mAh / g) far exceeding that of traditional graphite (372 mAh / g), have become a key direction for breaking through the energy density bottleneck of lithium-ion batteries. However, the volume expansion effect of silicon materials during lithium insertion / extraction, reaching up to 300%, leads to problems such as electrode pulverization, repeated rupture and regeneration of the SEI film, and peeling of active material from the current collector, severely restricting its industrialization process. To solve this problem, academia and industry have proposed to deposit silanes in porous carbon to nanoscale silicon particles and construct a porous carbon-silicon composite structure to buffer volume expansion, but existing technologies still face the following bottlenecks:

[0003] 1. Insufficient penetration of silane vapor deposition:

[0004] In traditional chemical vapor deposition (CVD) processes, silane (SiH4) gas has difficulty penetrating into micropores with a diameter of ≤1 nm due to surface tension, resulting in excessive silicon deposition at the pore opening and insufficient utilization of the internal pores (e.g., pore utilization <50%).

[0005] 2. Residual gas in the pores hinders silane diffusion:

[0006] Gas molecules such as H2O and O2 adsorbed within the porous carbon framework compete with silanes for adsorption sites during deposition, hindering silane diffusion and deposition, resulting in uneven silicon deposition. Residual gases can also cause silicon particles to grow in an island-like pattern within the pores, ultimately leading to localized stress concentration and particle cracking during charging and discharging.

[0007] 3. Low gas-solid contact efficiency in fluidized beds:

[0008] In traditional fluidized bed reactors, uneven mixing of silane and carrier gas forms a gas film barrier (thickness ≥ 1 μm), hindering mass transfer of silane to the carbon surface. Without enhancement measures, the penetration depth of silane within 10 nm pores is only 55%, and the size dispersion of deposited silicon particles is large, which is not conducive to the uniform deposition of experimental silicon in porous carbon.

[0009] The aforementioned problems result in insufficient initial coulombic efficiency, large volume expansion, and rapid degradation in the later stages of cycling for silicon-carbon materials, severely hindering their practical application in battery cells. To address these issues, the industry urgently needs an innovative process that can achieve uniform filling of silicon within a multi-level porous carbon framework while simultaneously enhancing the mechanical and ion transport properties of the carbon matrix, thereby further improving the electrochemical performance of silicon-carbon composite materials.

[0010] Numerous existing technologies report on silicon deposition in silicon-carbon composite materials, such as CN119008920A, CN119674026A, CN119683604A, and CN119208563A. However, none of these technologies have resolved the issues of insufficient silane vapor deposition head-off capability, residual gas in pores hindering silane diffusion, and low gas-solid contact efficiency in fluidized beds. Consequently, the electrochemical performance of the resulting silicon-carbon materials is not yet optimal. Summary of the Invention

[0011] The purpose of this invention is to systematically solve the problems of permeation, uniformity, and structural stability in the preparation of silicon-carbon composite materials through a multi-field coupling technology of supercritical carrier gas-ultrasound-intermittent deposition, and to provide a silicon-carbon composite material with uniform deposition of nano-silicon inside and outside the particles. This invention can improve the initial coulombic efficiency of silicon-carbon composite materials, reduce stress concentration and volume expansion during charge and discharge processes, and improve cycle stability. The invention provides the following technical solutions to achieve the above objectives:

[0012] A method for preparing silicon-carbon materials by vapor deposition based on supercritical carrier gas includes the following steps:

[0013] (S1) Vacuum degassing is performed on porous carbon material under heating conditions;

[0014] (S2) The porous carbon after desorption of gas is put into the reactor. Supercritical gas is used as the fluidizing gas. Silane gas is introduced under ultrasonic vibration conditions. After the silane gas is adsorbed into the pores of the porous carbon, the introduction of silane gas is stopped. The flow rate of supercritical gas is 3-5 times the flow rate of silane gas.

[0015] (S3) Heat the reactor to the silane decomposition temperature to form a uniform silicon layer in the porous carbon channels, then cool down and repeat step S2 until the material reaches the required silicon content.

[0016] (S4) An amorphous carbon layer is coated on the surface of the silicon deposition layer to form a core-shell structured silicon-carbon composite material.

[0017] Furthermore, in step (S1), the purpose of staged vacuum degassing under heating is to remove the previously adsorbed gas from the pore structure and clear the pore structure. Preferably, a staged heating vacuum degassing process with gradual temperature increases is used. During the heating vacuum degassing process, the temperature rises from 60-80℃ to 250-300℃, while the pressure increases from 10...3 The Pa order of magnitude is reduced to 10. -2 The pressure is on the order of Pa, divided into 3-5 stages, for example, 4 stages: the first stage has a temperature of 80-120 ℃ and the pressure drops to 1×10⁻⁶. 3 Pa to 5×10 3 The first stage involves maintaining the pressure at 1 Pa for 10-60 minutes; the second stage involves maintaining the pressure at 120-180℃ for 10-60 minutes; the third stage involves maintaining the pressure at 180-225℃ for 20-60 minutes; and the fourth stage involves maintaining the pressure at 225-290℃ for 20-60 minutes.

[0018] This invention employs a segmented heating degassing method, which can control the degassing rate of adsorbed gas in the porous carbon framework, allowing the adsorbed gas to be released at a stable rate. This maintains the integrity of the porous carbon channel structure and avoids local pressure imbalances caused by rapid degassing in local channels of the porous carbon framework, which can lead to the collapse and shrinkage of the channel structure. This helps to achieve uniform silicon deposition inside and outside the porous carbon framework.

[0019] Further, in step (S1), the heating rate for degassing is 0.5-10 ℃ / min, preferably 1-5 ℃ / min.

[0020] Further, in step (S1), the porous carbon is sourced from at least one of biomass, resin, and coke. The biomass porous carbon is sourced from at least one of coconut shell, palm shell, and apricot shell; the resin porous carbon is sourced from at least one of phenolic resin, furfural resin, and epoxy resin; and the coke porous carbon is sourced from at least one of petroleum coke, needle coke, and anthracite. The porous carbon is activated by at least one of physical activation and chemical activation. The physical activation method is at least one of steam, carbon dioxide, and oxygen activation; and the chemical activation method is at least one of alkali activation, phosphoric acid activation, and zinc chloride activation.

[0021] Further, in step (S1), the median particle size D50 of the porous carbon is preferably 1-15 μm, more preferably 3-10 μm; the specific surface area is preferably 1300-2800 m². 2 / g, preferably 1600-2400 m 2 / g; the pore volume of the porous carbon is preferably 0.5-1.2 cm³. 3 / g, preferably 0.8-1.0 cm 3 / g; wherein the micropore volume accounts for 60-95% of the total pore volume, the mesopore volume accounts for 1-40% of the total pore volume, and the macropore volume accounts for <5% of the total pore volume.

[0022] Further, in step (S2), the supercritical gas is at least one of carbon dioxide, nitrogen, helium, neon, argon, krypton, and xenon at a certain temperature and pressure, preferably carbon dioxide. The inventors have discovered that using supercritical carbon dioxide as a carrier gas can maximize the efficiency of silicon deposition. The supercritical temperature and pressure of each different gas are different and can be determined by the art based on phase diagrams. For example, for carbon dioxide, a temperature > 31.1°C and a pressure > 7.38 MPa constitute a supercritical state. The silane gas includes, but is not limited to, at least one of silane, disilane, propane, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride.

[0023] Preferably, in step (S2), the flow rate of the supercritical gas is 10-300 L / min, more preferably 100-150 L / min; the flow rate of the silane gas is 0.5-60 L / min, more preferably 20-50 L / min; the aeration time is 1-30 min, more preferably 5-20 min; and the flow rate of the supercritical gas is 3-5 times that of the silane gas. Controlling the ratio of the supercritical gas flow rate to the silane gas flow rate within the above range can promote the diffusion of silane into the porous carbon, thereby achieving uniform deposition of silicon inside and outside the porous carbon particles, further improving cycle stability. At the same time, it avoids the problem of high mass production cost and complex process caused by excessively low silane flow rate leading to low deposition amount per cycle and increased cycle number required to achieve the same deposition amount.

[0024] Further, in step (S2), the frequency of ultrasonic vibration is 20-100 kHz, preferably 30-50 kHz. At this frequency, ultrasound can effectively break up bubbles and particle clusters in the reactor, thereby achieving more uniform gas-solid contact, improving the uniformity of silicon deposition, while ensuring sufficient penetration depth to avoid power attenuation at the center of the device, thus ensuring more uniform gas-solid contact at every point in the reactor. The ultrasonic power in the reactor is 100-400 W / m. 3 Preferred 150-200W / m 3 At this power level, bubbles and particle clusters can be effectively eliminated without the power density being too high, which would damage the structure of the porous carbon skeleton.

[0025] Furthermore, in step (S3), the heating rate of the reactor is 1-10 ℃ / min, the pyrolysis temperature of the silicon-containing gas is selected according to the different silane gases, generally 400-700 ℃, and the holding time is 10-30 min.

[0026] Furthermore, in step (S3), the number of repetitions is such that the silicon mass content of the composite material obtained in step (S3) is 40-60%, preferably 43-58%, and more preferably 45-55%.

[0027] Further, in step (S4), the carbon source gas is at least one of methane, acetylene, ethylene, propylene, propyne, methane, ethane, and propane. The coating process temperature is preferably 450-750 °C, the carbon source gas flow rate is preferably 3-20 L / min, and the holding time is preferably 3-12 h. The thickness of the carbon coating layer after carbon coating is 1-10 nm, preferably 3-7 nm.

[0028] This invention employs a heating vacuum step to first desorb the gas adsorbed in the porous carbon framework, providing a smooth path for the diffusion and adsorption of silane gas. Supercritical fluidization is used to enhance the dispersion of the silicon source gas in the reactor and the diffusion through the porous carbon nanopore structure, helping the silicon source gas to rapidly reach the deep pores of the porous carbon framework and significantly enhancing its adsorption effect in ultramicropores <1 nm. Coupled with ultrasonic dispersion technology, bubbles and particle clusters affecting gas-solid contact in the reactor are broken up without affecting the carbon framework's structure, reducing gas film mass transfer resistance on the particle surface, thereby providing better gas-solid contact and mass transfer of the silicon source gas. The combination of these technologies achieves ultra-uniform deposition of the silicon source gas in the porous carbon framework, thereby reducing side reactions on the particle's inner surface, improving initial coulombic efficiency, reducing stress concentration and volume expansion during charge and discharge, and improving cycle stability. Attached Figure Description

[0029] Figure 1 A scanning electron microscope image of the silicon-carbon composite material prepared in Example 1;

[0030] Figure 2 The first charge-discharge curve of the silicon-carbon composite material prepared in Example 1 is shown. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] The scanning electron microscope (SEM) used was a Regulus 8100, and the transmission electron microscope (TEM) used was a JEM-2100F.

[0034] Example 1

[0035] (S1) Degassing of porous carbon materials: First, 10 kg of BET with a specific surface area of ​​2100 m² 2 / g, pore volume 0.89 cm³ 3Porous carbon material with a micropore content of 82% and a D50 of 7 μm was introduced into a vacuum chamber, heated to 100 °C, and then degassed under vacuum until it reached 10 °C. 3 Pa, maintain for 15 min, then heat to 150 ℃, vacuum degas to 10 Pa, maintain for 20 min, then heat to 200 ℃, vacuum degas to 0.1 Pa, maintain for 25 min, finally heat to 260 ℃, vacuum degas to 0.01 Pa, maintain for 30 min to complete degassing, and obtain the degassed porous carbon material;

[0036] (S2) Adsorption of silicon source gas: The degassed porous carbon material obtained in step (S1) is added to the reactor. An ultrasonic generator is installed in the reactor, and the ultrasonic vibration frequency is turned on at 30 Hz, with the ultrasonic power set to 150 W / m. 3 CO2 was introduced at a flow rate of 100 L / min at 50 ℃ and 10 MPa to bring it to a supercritical state, and silane gas was introduced at a flow rate of 20 L / min. After 15 min, the gas introduction and ultrasonic vibration were stopped.

[0037] (S3). Silicon deposition: Heat to 580 °C at a heating rate of 5 °C / min, hold for 20 min, then cool to 50 °C. Repeat steps (S2) and (S3) a total of 15 times to make the silicon mass content of the composite material obtained in step S3 52.4%.

[0038] (S4). Coating of silicon-carbon composite material: The reactor was heated to 650 °C and methane gas was introduced at a rate of 13 L / min and kept at the temperature for 4 h to obtain silicon-carbon composite anode material with a carbon shell coating on the surface. The thickness of the carbon coating layer was 4-6 nm.

[0039] Figure 1 The image shows a scanning electron microscope (SEM) image of the silicon-carbon composite anode material prepared in Example 1, with a particle size of approximately 8 µm.

[0040] Figure 2 The first charge-discharge curve of the silicon-carbon composite anode material prepared in Example 1 is shown.

[0041] Example 2

[0042] The other conditions and operations are the same as in Example 1, except that in step (S1), the pore volume of 10 kg is 0.89 cm³. 3 / g of porous carbon is replaced with 10 kg of porous carbon with a pore volume of 1.01 cm³. 3 / g porous carbon; repeat steps (S2) and (S3) to make the silicon mass content of the composite material obtained in step (S3) 54.9%.

[0043] Example 3

[0044] The other conditions and operations are the same as in Example 1, except that in step (S1), the pore volume of 10 kg is 0.89 cm³. 3 / g of porous carbon is replaced with 10 kg of porous carbon with a pore volume of 0.75 cm³. 3 / g porous carbon; repeat steps (S2) and (S3) to make the silicon mass content of the composite material obtained in step (S3) 48.9%.

[0045] Example 4

[0046] Other conditions and operations are the same as in Example 1, except that steps (S2) and (S3) are repeated so that the silicon mass content of the composite material obtained in step (S3) is 58.2%.

[0047] Example 5

[0048] The other conditions and operations are the same as in Example 1, except that steps (S2) and (S3) are repeated so that the silicon mass content of the composite material obtained in step (S3) is 46.8%.

[0049] Example 6

[0050] The other conditions and operations are the same as in Example 1, except that in step (S2), the flow rate of supercritical CO2 is 150 L / min and the flow rate of silane is 50 L / min.

[0051] Example 7

[0052] The other conditions and operations are the same as in Example 1, except that in step (S2), instead of introducing CO2 at 100 L / min under conditions of 50°C and 10 MPa, nitrogen is introduced at 100 L / min under conditions of 60°C and 4 MPa.

[0053] Example 8

[0054] The other conditions and operations are the same as in Example 1, except that in step (S2), CO2 is introduced at 100 L / min at 50°C and 10 MPa, while argon is introduced at 100 L / min at 70°C and 5 MPa.

[0055] Example 9

[0056] The other operations are the same as in Example 1, except that the segmented degassing process in step (S1) is changed to: 10 kg of gas with a pore volume of 0.89 cm³ 3 / g of porous carbon material was added to a vacuum chamber, heated to 260 ℃ and degassed to 0.01 Pa, and maintained for 60 min.

[0057] Comparative Example 1

[0058] The other operations are the same as in Example 1, except that in step (S2): CO2 is introduced at 50 °C and 10 MPa instead of at 50 °C and normal pressure.

[0059] Comparative Example 2

[0060] The other operations are the same as in Example 1, except that in step (S2): there is no ultrasonic vibration assistance.

[0061] Comparative Example 3

[0062] (S1) The specific surface area of ​​10 kgBET is 2100 m² 2 / g, pore volume 0.89 cm³ 3 / g, porous carbon material with a micropore content of 82% and a D50 of 7um was added to the reactor and heated to 580°C at a heating rate of 5°C / min. A mixture of silane and argon in a volume ratio of 1:4 was introduced and the silane flow rate was 20L / min to perform silane deposition. By controlling the deposition time, the silicon mass content of the obtained silicon-carbon material was made to be 52.4%, which is the same as in Example 1.

[0063] (S2) Coating of silicon-carbon composite material: The reactor was heated to 650 °C and methane gas was introduced at a rate of 13 L / min and kept at the temperature for 4 h to obtain silicon-carbon composite anode material with a carbon shell coating on the surface.

[0064] Comparative Example 4

[0065] The other conditions and operations are the same as in Example 1, except that in step (S2), the flow rate of supercritical CO2 is 120 L / min.

[0066] Comparative Example 5

[0067] The other conditions and operations are the same as in Example 1, except that in step (S2), the supercritical CO2 flow rate is 50 L / min.

[0068] Application examples

[0069] The electrochemical performance of the silicon-based anode materials prepared in the above examples and comparative examples was tested according to the following method: The prepared silicon-carbon composite material, carbon black, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite binder were mixed in a mass ratio of 80:10:10 to form a slurry (where the mass ratio of CMC and SBR was 1:1). The slurry was uniformly coated onto a copper foil current collector and dried under vacuum for 12 h to form a working electrode. A lithium sheet was used as the counter electrode, a glass fiber membrane (purchased from Whatman Ltd., UK) was used as the separator, and 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) was used as the electrolyte. 1% VC and 5% FEC were added to the electrolyte. The cells were assembled into coin cells in an argon-atmosphere inert gas glove box from Braun, Germany.

[0070] Electrochemical analysis was performed on the silicon-carbon composite material prepared in Example 1, and the results are as follows: Figure 2 As shown. The charge / discharge range is 0-1.5 V. Under a charge / discharge current density of 0.2C, the material capacity can reach 2165.0 mAh / g, with an initial coulombic efficiency of 93.8%. The battery retains a capacity of up to 96.2% after 100 cycles at 1C, proving that the silicon-carbon composite material obtained in this invention has good cycle stability.

[0071] Charge-discharge tests were conducted on the negative electrode materials of other embodiments and comparative examples using the method described above, and the results are shown in Table 1 below:

[0072] Table 1 Electrochemical performance test

[0073] .

[0074] In summary, the silicon-carbon composite material prepared by the supercritical carrier gas-ultrasound-intermittent deposition coupling technology provided by this invention exhibits good deposition uniformity and structural stability, resulting in higher initial coulombic efficiency and stable cycle performance of the battery. The preparation method provided by this invention is simple and easy to implement, and suitable for industrial-scale production.

Claims

1. A method for the production of a silicon-carbon material by vapor deposition based on a supercritical carrier gas, characterized in that, The method comprises the following steps: (S1) vacuum degassing the porous carbon material in a heated state; using a gradual temperature increase in a staged heating vacuum degassing, during the heating vacuum degassing, the temperature is increased from 60-80 °C to 250-300 °C, while the pressure is reduced from 10 3 Pa order of magnitude to 10 -2 Pa order of magnitude; (S2) Put the porous carbon after desorption gas into the reactor, take supercritical state gas as fluidized gas, under the condition of ultrasonic vibration, put in silane gas, after the silane gas is adsorbed in the pore of the porous carbon, stop putting in the silane gas; the flow of the supercritical state gas is 3-5 times of the flow of the silane gas; the flow rate of the supercritical state gas is 10-300 L / min, the flow rate of the silane gas is 0.5-60 L / min, and the aeration time is 1-30 min; the frequency of the ultrasonic vibration is 20-100 kHz, and the ultrasonic power is 100-400 W / m 3 ; (S3) heating the reactor to a silane cracking temperature to form a uniform silicon layer in the pores of the porous carbon, then cooling and repeating step S2 until the material reaches the desired silicon content; (S4) coating an amorphous carbon layer on the surface of the silicon deposition layer to form a core-shell structure silicon-carbon composite material.

2. The production method according to claim 1, characterized by, In step (S1), the vacuum degassing under heating is divided into four stages: the temperature of the first stage is 80-120 ℃, the pressure is reduced to 1x10 3 Pa to 5x10 3 Pa, and maintained for 10-60 min; the temperature of the second stage is 120-180 ℃, the pressure is reduced to 1 Pa to 100 Pa, and maintained for 10-60 min; the temperature of the third stage is 180-225 ℃, the pressure is reduced to 0.1 Pa to 1 Pa, and maintained for 20-60 min; and the temperature of the fourth stage is 225-290 ℃, the pressure is reduced to 0.01 Pa to 0.1 Pa, and maintained for 20-60 min.

3. The preparation method according to claim 1, characterized in that, In step (S1), the heating and degassing rate is 0.5-10 ℃ / min.

4. The method of claim 1, wherein, In step (S1), the median particle size D50 of the porous carbon is 1-15 μm, the specific surface area is 1300-2800 m 2 / g, the pore volume is 0.5-1.2 cm 3 / g, the micropore volume accounts for 60-95% of the total pore volume, the mesopore volume accounts for 1-40% of the total pore volume, and the macropore volume accounts for <5% of the total pore volume.

5. The preparation method according to claim 1, characterized in that, In step (S2), the supercritical state gas is selected from at least one of carbon dioxide, nitrogen, helium, neon, argon, krypton, and xenon; and / or the silane gas is selected from at least one of monosilane, disilane, trisilane, monochlorohydrosilane, dichlorohydrosilane, trichlorohydrosilane, and silicon tetrachloride.

6. The method of claim 1, wherein, In step (S2), the flow rate of the supercritical state gas is 100-150 L / min, the flow rate of the silane gas is 20-50 L / min, and the aeration time is 5-20 min.

7. The preparation method according to claim 1, characterized in that, In step (S3), the heating rate of the reactor is 1-10 ℃ / min, the cracking temperature is 400-700 ℃, and the holding time is 10-30 min; the number of repetitions is such that the silicon mass content of the composite material obtained in step (S3) is 40-60%.

8. The preparation method according to claim 1, characterized in that, In step (S4), the carbon source gas used for coating an amorphous carbon layer on the surface of the silicon deposition layer is selected from at least one of methane, acetylene, ethylene, propylene, propyne, ethane, and propane, the surface coating amorphous carbon layer process temperature is 450-750 ℃, the carbon source gas flow rate is 3-20 L / min, and the holding time is 3-12 h; after carbon coating, the carbon coating layer thickness is 1-10 nm.

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