Preparation method of vapor deposition silicon carbon material based on supercritical carrier gas

Abstract

The invention belongs to the field of silicon-carbon negative electrode material manufacturing, and particularly relates to a preparation method of a vapor deposition silicon-carbon material based on supercritical carrier gas. The method comprises the following steps: carrying out vacuum degassing on a porous carbon material in a heating state, then taking supercritical gas as carrier gas, assisting with ultrasonic vibration, introducing silicon-containing gas to carry out silicon deposition, and repeatedly carrying out operation until the required silicon content is reached; and finally, introducing a carbon source gas for carbon coating to obtain the silicon-carbon composite material with the core-shell structure. According to the preparation method, uniform deposition of silicon in a porous carbon skeleton is realized through silane vapor deposition with supercritical fluid as carrier gas under the assistance of ultrasonic vibration, the first coulombic efficiency is improved, stress concentration and volume expansion in the charging and discharging process are reduced, and the cycling stability is improved.

Description

Technical Field

[0001] The present invention belongs to the field of silicon-carbon negative electrode material manufacturing, and in particular relates to a method for preparing a vapor-deposited silicon-carbon material based on a supercritical carrier gas. Background Art

[0002] With the continued growth in demand for high-energy-density batteries in new energy vehicles and portable electronic devices, silicon-based negative electrode material systems have become a key direction for breaking through the energy density bottleneck of lithium-ion batteries due to their theoretical specific capacity (4200 mAh / g) far exceeding that of traditional graphite (372 mAh / g). However, the volume expansion effect of silicon materials during the lithium insertion / extraction process, which is as high as 300%, leads to problems such as electrode pulverization, repeated rupture and regeneration of the SEI film, and separation of active materials from the current collector, which seriously restricts its industrialization process. To solve this problem, academia and industry have proposed to deposit silane in porous carbon, nano-size silicon particles, and construct a porous carbon-silicon composite structure to buffer the volume expansion, but the existing technology still has the following bottlenecks: 1. Insufficient penetration ability of silane vapor deposition: In traditional chemical vapor deposition (CVD) processes, silane (SiH4) gas has difficulty penetrating into micropores with a pore size of ≤1 nm due to surface tension, resulting in excessive silicon deposition at the pore entrance and insufficient internal pore utilization (e.g., pore utilization <50%).

[0003] 2. Residual gas in the pores hinders the diffusion of silane: Gas molecules like H₂O and O₂ adsorbed within the porous carbon framework compete with silane for adsorption sites during the deposition process, hindering silane diffusion and deposition, leading to uneven silicon deposition. Residual gas can also cause silicon particles to grow as islands within the pores, ultimately leading to localized stress concentrations and particle cracking during charge and discharge.

[0004] 3. The gas-solid contact efficiency of the fluidized bed is low: In conventional fluidized-bed reactors, uneven mixing of silane and carrier gas forms a gas film barrier (thickness ≥ 1 μm), hindering the mass transfer of silane to the carbon surface. Without enhancement measures, the penetration depth of silane within pores with a diameter of 10 nm is only 55%, and the deposited silicon particles have a wide size distribution, hindering the uniform deposition of silicon in the porous carbon.

[0005] These issues have led to low initial Coulombic efficiency, large volume expansion, and rapid decay in the later stages of cycling in silicon-carbon materials, severely hindering their practical application in battery cells. To address these challenges, the industry urgently needs an innovative process that can uniformly fill silicon within a multi-level porous carbon framework while simultaneously enhancing the mechanical and ion transport properties of the carbon matrix to further improve the electrochemical performance of silicon-carbon composites.

[0006] There are many reports on silicon deposition in the prior art of silicon-carbon composite materials, such as CN119008920A, CN119674026A, CN119683604A, and CN119208563A. However, none of them can solve the problems of insufficient silicon deposition, gas residue in the pores hindering the diffusion of silane, and low gas-solid contact efficiency of the fluidized bed, resulting in suboptimal electrochemical performance of the obtained silicon-carbon material. SUMMARY

[0007] The present application aims to systematically solve the problems of permeation, uniformity, and structural stability in the preparation of silicon-carbon composite materials by using the supercritical carrier gas-ultrasonic-intermittent deposition multi-field coupling technology, and to provide a silicon-carbon composite material with uniform deposition of nano-silicon inside and outside the particles. The present application can improve the initial coulomb efficiency of the silicon-carbon composite material, reduce stress concentration and volume expansion during charging and discharging, and improve the cycle stability. The present application provides the following technical solutions to achieve the above-mentioned purposes: A preparation method of a silicon-carbon material by gas phase deposition based on supercritical carrier gas, comprising the following steps: (S1) vacuum degassing the porous carbon material under heating; (S2) after desorption of the gas, the porous carbon is put into a reactor, and a supercritical state gas is used as the fluidizing gas. Under ultrasonic vibration, silane gas is introduced, and after the silane gas is adsorbed in the pores of the porous carbon, the introduction of silane gas is stopped. The flow rate of the supercritical state gas is 3-5 times that of the silane gas; (S3) the reactor is heated to the silane cracking temperature, forming a uniform silicon layer in the pores of the porous carbon. Then, the temperature is lowered and step S2 is repeated until the material reaches the desired silicon content; (S4) an amorphous carbon layer is coated on the surface of the silicon deposition layer to form a core-shell structure silicon-carbon composite material.

[0008] Further, in step (S1), the purpose of stepwise vacuum degassing under heating is to remove the previously adsorbed gas in the pore structure and to unblock the pore structure. Preferably, the vacuum degassing is performed by gradually increasing the temperature in stages. During the heating and vacuum degassing process, the temperature is increased from 60-80℃ to 250-300℃, and the pressure is reduced from 10 3 Pa to 10 -2 Pa order, divided into 3-5 stages, such as 4 stages: the temperature of the first stage is 80-120℃, and the pressure is reduced to 1×10 3 Pa to 5×10 3Pa, maintain for 10-60 min; the temperature of the second stage is 120-180℃, the pressure is reduced to 1 Pa to 100 Pa, and maintain for 10-60 min; the temperature of the third stage is 180-225℃, the pressure is reduced to 0.1Pa to 1 Pa, and maintain for 20-60 min; the temperature of the fourth stage is 225-290℃, the pressure is reduced to 0.01 Pa to 0.1Pa, and maintain for 20-60 min.

[0009] The present invention adopts a segmented heating degassing method, which can control the degassing rate of the adsorbed gas in the porous carbon skeleton, so that the adsorbed gas can be released at a steady rate, thereby maintaining the integrity of the porous carbon pore structure, avoiding the rapid degassing of local pores in the porous carbon skeleton, resulting in local pressure imbalance and collapse and shrinkage of the pore structure, and helping to achieve uniform silicon deposition inside and outside the porous carbon skeleton.

[0010] Furthermore, in step (S1), the heating rate of the degassing is 0.5-10°C / min, preferably 1-5°C / min.

[0011] Furthermore, in step (S1), the porous carbon is derived from at least one of biomass, resin, and coke. The biomass porous carbon is derived from at least one of coconut shells, palm shells, and apricot shells; the resin porous carbon is derived from at least one of phenolic resins, furfural resins, and epoxy resins; and the coke porous carbon is derived 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 water vapor, carbon dioxide, and oxygen activation; and the chemical activation method is at least one of alkali activation, phosphoric acid activation, and zinc chloride activation.

[0012] Furthermore, in step (S1), the median particle size D50 of the porous carbon is preferably 1-15 μm, preferably 3-10 μm; the specific surface area is preferably 1300-2800 m 2 / g, preferably 1600-2400 m 2 / g; the pore volume of the porous carbon is preferably 0.5-1.2 cm 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 preferably 1-40% of the total pore volume, and the macropore volume accounts for preferably <5% of the total pore volume.

[0013] Furthermore, 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 found that using carbon dioxide in a supercritical state as a carrier gas can maximize the efficiency of silicon deposition. The temperature and pressure of the supercritical state of each different gas are different, which can be mastered in this field according to the phase diagram. For example, for carbon dioxide, the temperature is greater than 31.1°C and the pressure is greater than 7.38MPa, which is a supercritical state. The silane gas includes but is not limited to at least one of monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride.

[0014] Preferably, in step (S2), the flow rate of the supercritical state gas is 10-300 L / min, preferably 100-150 L / min; the flow rate of the silane gas is 0.5-60 L / min, preferably 20-50 L / min, and the ventilation time is 1-30min, preferably 5-20min; and the flow rate of the supercritical state gas is 3-5 times the flow rate of the silane gas. Controlling the ratio of the flow rate of the supercritical state gas and the flow rate of the silane gas within the above range can promote the diffusion of silane into the porous carbon, so as to achieve uniform deposition of silicon inside and outside the porous carbon particles, further improve the cycle stability, and avoid the silane flow rate being too small, resulting in a single deposition amount that is too low, and achieving the problem of high mass production cost and complicated process caused by the increase in the number of cycles required for the same deposition amount.

[0015] Furthermore, in step (S2), the frequency of the 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 and improving the uniformity of silicon deposition, while ensuring sufficient penetration depth to avoid power attenuation at the center of the equipment, thereby ensuring that more uniform gas-solid contact can be achieved at every position in the reactor. The ultrasonic power in the reactor is 100-400W / m 3 , preferably 150-200W / m 3 At this power, bubbles and particle clusters can be effectively eliminated without causing structural damage to the porous carbon skeleton due to excessive power density.

[0016] Furthermore, in step (S3), the heating rate of the reactor is 1-10°C / min, the cracking temperature of the silicon-containing gas is selected according to different silane gases, generally 400-700°C, and the holding time is 10-30 min.

[0017] 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%, more preferably 45-55%.

[0018] Further, in step (S4), the carbon source gas is at least one of methane, acetylene, ethylene, propylene, propyne, methane, ethane, propane, the coating process temperature is preferably 450-750 ℃, the carbon source gas flow is preferably 3-20 L / min, and the holding time is preferably 3-12 h. After carbon coating, the carbon coating layer thickness is 1-10 nm, preferably 3-7 nm.

[0019] The present application provides a smooth path for the diffusion and adsorption of silane gas by heating the vacuum step to first desorb the gas adsorbed in the porous carbon skeleton, uses supercritical fluid fluidization to enhance the dispersion of the silicon source gas in the reactor and the diffusion of the porous carbon nanopore structure, helps the silicon source gas to quickly reach the pore structure in the deep part of the porous carbon skeleton, and significantly enhances its adsorption effect in the ultramicropore of <1 nm. Coupling with ultrasonic dispersion technology, the gas bubbles and particle groups affecting the gas-solid contact in the reactor are broken without affecting the structure of the carbon skeleton, the gas film mass transfer resistance on the particle surface is reduced, thereby providing better gas-solid contact and mass transfer effect of the silicon source gas. The above various technologies are combined to achieve the super-uniform deposition of the silicon source gas in the porous carbon skeleton, thereby reducing the side reactions on the internal surface of the particles, improving the first coulomb efficiency, reducing the stress concentration and volume expansion during charging and discharging, and improving the cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A scanning electron microscope photograph of the silicon-carbon composite material prepared in Example 1; Figure 2 A first charge-discharge curve of the silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0021] The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments.

[0022] In the following examples, the experimental methods are conventional methods unless otherwise specified; and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0023] The scanning electron microscope (SEM) is a scanning electron microscope Regulus 8100, and the transmission electron microscope (TEM) is a JEM-2100F.

[0024] Example 1 (S1) Degassing of porous carbon material: first, 10 kg of porous carbon material with a BET specific surface area of 2100 m 2 / g, a pore volume of 0.89 cm 3 / g, a micropore ratio of 82%, and a D50 of 7 um is put into a vacuum chamber, heated to 100 ℃ and vacuum degassed to 10 3Pa, maintained for 15 min, then heated to 150 ° C, vacuum degassed to 10 Pa, maintained for 20 min, then heated to 200 ° C, vacuum degassed to 0.1 Pa, maintained for 25 min, and finally heated to 260 ° C, vacuum degassed to 0.01 Pa, maintained for 30 min to complete the degassing, and obtain the degassed porous carbon material; (S2) Adsorption of silicon source gas: The degassed porous carbon material obtained in step (S1) was added to a reactor, an ultrasonic generator was set in the reactor, the frequency of ultrasonic vibration was set to 30 Hz, and the ultrasonic power was set to 150 W / m 3 At 50 °C and 10 MPa, CO2 was introduced at a flow rate of 100 L / min to achieve a supercritical state, and monosilane gas was introduced at a flow rate of 20 L / min. After 15 minutes, ventilation and ultrasonic vibration were stopped. (S3) Silicon-silicon deposition: Raise the temperature 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, so that the silicon mass content of the composite material obtained in step S3 is 52.4%.

[0025] (S4) Coating of silicon-carbon composite materials: The reactor was heated to 650°C and methane gas was introduced at a flow rate of 13 L / min for 4 h to obtain a silicon-carbon composite negative electrode material coated with a carbon shell. The thickness of the carbon coating layer was 4-6 nm.

[0026] Figure 1 This is a scanning electron microscope photograph of the silicon-carbon composite negative electrode material prepared in Example 1. The particle size is about 8 μm.

[0027] Figure 2 This is the first charge and discharge curve of the silicon-carbon composite negative electrode material prepared in Example 1.

[0028] Example 2 Other conditions and operations were the same as those in Example 1, except that in step (S1), the pore volume of 10 kg was 0.89 cm 3 / g of porous carbon was replaced by 10 kg with a pore volume of 1.01 cm 3 / g of porous carbon; repeat steps (S2) and (S3) so that the silicon mass content of the composite material finally obtained in step (S3) is 54.9%.

[0029] Example 3 Other conditions and operations were the same as those in Example 1, except that in step (S1), the pore volume of 10 kg was 0.89 cm 3 / g of porous carbon was replaced by 10 kg with a pore volume of 0.75 cm 3 / g of porous carbon; repeat steps (S2) and (S3) so that the silicon mass content of the composite material finally obtained in step (S3) is 48.9%.

[0030] Example 4 Other conditions and operations were the same as those in Example 1, except that steps (S2) and (S3) were repeated until the silicon mass content of the composite material obtained in step (S3) was 58.2%.

[0031] Example 5 Other conditions and operations were the same as those in Example 1, except that steps (S2) and (S3) were repeated so that the silicon mass content of the composite material obtained in step (S3) was 46.8%.

[0032] Example 6 Other conditions and operations are the same as those in Example 1, except that in step (S2), the flow rate of supercritical CO2 is 150 L / min, and the flow rate of monosilane is 50 L / min.

[0033] Example 7 Other conditions and operations were the same as those in Example 1, except that in step (S2), the flow of CO2 at 100 L / min under the conditions of 50°C and 10 MPa was changed to the flow of nitrogen at 100 L / min under the conditions of 60°C and 4 MPa.

[0034] Example 8 Other conditions and operations were the same as those in Example 1, except that in step (S2), the flow of CO2 at 100 L / min under the conditions of 50°C and 10 MPa was changed to the flow of argon at 100 L / min under the conditions of 70°C and 5 MPa.

[0035] Example 9 Other operations are the same as in Example 1, except that the segmented degassing process in step (S1) is changed to: 3 / g porous carbon material was put into a vacuum chamber, heated to 260 °C and vacuum degassed to 0.01 Pa for 60 min.

[0036] Comparative Example 1 Other operations were the same as those in Example 1, except that in step (S2), the CO2 was introduced under the conditions of 50°C and 10 MPa instead of 50°C and normal pressure.

[0037] Comparative Example 2 Other operations are the same as those in Example 1, except that in step (S2), there is no ultrasonic vibration assistance.

[0038] Comparative Example 3 (S1) 10 kg BET surface area 2100 m 2 / g, and a pore volume of 0.89 cm 3 / g, a porous carbon material with a micropore ratio of 82% and a D50 of 7 μm was put into a reactor, and the temperature was raised to 580°C at a heating rate of 5°C / min. A mixed gas of monosilane and argon in a volume ratio of 1:4 was introduced at a monosilane flow rate of 20 L / min to perform silane deposition. The deposition time was controlled so that the silicon mass content of the obtained silicon-carbon material was 52.4%, which was the same as that in Example 1; (S2) Coating of silicon-carbon composite material: The reactor was heated to 650°C and methane gas was introduced at a flow rate of 13 L / min for 4 h to obtain a silicon-carbon composite negative electrode material coated with a carbon shell on the surface.

[0039] Comparative Example 4 Other conditions and operations are the same as those in Example 1, except that in step (S2), the flow rate of supercritical CO2 is 120 L / min.

[0040] Comparative Example 5 Other conditions and operations were the same as those in Example 1, except that in step (S2), the flow rate of supercritical CO2 was 50 L / min.

[0041] Application Examples The electrochemical properties of the silicon-based negative electrode materials prepared in the above examples and comparative examples were tested according to the following method: the prepared silicon-carbon composite material, carbon black, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite binder were mixed in a mass ratio of 80:10:10 to form a slurry (wherein the mass ratio of CMC and SBR was 1:1), the slurry was evenly coated on a copper foil current collector, and vacuum dried for 12 h to prepare a working electrode; a lithium sheet was used as a counter electrode, a glass fiber membrane (purchased from Whatman, UK) was used as a separator, 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 an electrolyte, 1% by volume of VC and 5% by volume of FEC were added to the electrolyte, and button cells were assembled in an argon atmosphere in a Braun inert gas glove box in Germany.

[0042] The electrochemical analysis test of the silicon-carbon composite material prepared in Example 1 was carried out, and the results were as follows: Figure 2 The charge-discharge range is 0-1.5 V. At a current density of 0.2C, the material capacity reaches 2165.0 mAh / g, with a first-cycle coulombic efficiency of 93.8%. After 100 cycles at 1C, the battery retains a capacity of 96.2%, demonstrating the excellent cycling stability of the silicon-carbon composite material obtained by this invention.

[0043] The negative electrode materials of other embodiments and comparative examples were subjected to charge and discharge tests according to the above method. The results are shown in Table 1 below: Table 1 Electrochemical performance test .

[0044] In summary, the silicon-carbon composite material prepared by the coupled supercritical gas-ultrasound-intermittent deposition technique provided by the present invention exhibits excellent deposition uniformity and structural stability, resulting in batteries with higher initial coulombic efficiency and stable cycling performance. The preparation method provided by the present invention is simple and easy to implement, making it suitable for industrial-scale production.

Claims

1. A method for preparing a silicon-carbon material by vapor deposition using a supercritical carrier gas, characterized in that: The following steps are involved: (S1) vacuum degassing the porous carbon material under heating; (S2) placing the porous carbon after desorption of gas into a reactor, using supercritical gas as fluidizing gas, and introducing silane gas 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 the supercritical gas is 3-5 times the flow rate of the silane gas; (S3) heating the reactor to the silane cracking temperature to form a uniform silicon layer in the porous carbon pores, then cooling the reactor and repeating step S2 until the material reaches the desired silicon content; (S4) An amorphous carbon layer is coated on the surface of the silicon deposited layer to form a core-shell structured silicon-carbon composite material.

2. The preparation method according to claim 1, characterized in that In step (S1), a gradually increasing temperature staged heating vacuum degassing is used. During the heating vacuum degassing process, the temperature is increased from 60-80°C to 250-300°C, and the pressure is increased from 10 3 Pa order of magnitude reduced to 10 -2 Pa order of magnitude.

3. The preparation method according to claim 1, characterized in that In step (S1), vacuum degassing is carried out under heating conditions in four stages: the temperature of the first stage is 80-120 °C, and the pressure is reduced to 1×10 3 Pa to 5×10 3 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; 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.

4. The preparation method according to claim 1, characterized in that In step (S1), the heating rate for degassing is 0.5-10°C / min.

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

6. The preparation method according to claim 1, characterized in that In step (S2), the supercritical 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, monochlorosilane, dichlorosilane, trichlorosilane, and silicon tetrachloride.

7. The preparation method according to claim 1, characterized in that In step (S2), the flow rate of the supercritical gas is 10-300 L / min, the flow rate of the silane gas is 0.5-60 L / min, and the ventilation time is 1-30 min; and / or The frequency of ultrasonic vibration is 20-100 kHz and the ultrasonic power is 100-400 W / m 3 .

8. The preparation method according to claim 1, characterized in that In step (S2), the flow rate of the supercritical gas is 100-150 L / min, the flow rate of the silane gas is 20-50 L / min, and the ventilation time is 5-20 min.

9. The preparation method according to claim 1, characterized in that In step (S3), the heating rate of the reactor is 1-10°C / min, the cracking temperature is 400-700°C, 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%.

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

Images