A low-expansion porous silicon-carbon composite material, a preparation method and applications

Abstract

The application discloses a kind of low expansion porous silicon-carbon composite material, preparation method and application, lithium ion battery negative electrode material technical field.The low expansion porous silicon-carbon composite material provided by the application anchors lithium ion by functionalized porous silicon surface, then generates artificial SEI film in-situ in porous silicon pore and surface using liquid phase precipitation reaction, solves the problem of uneven SEI film growth;Carbon nanotube is embedded between porous silicon particles, the first carbon source is used to bond porous silicon and carbon nanotube together, and the porous silicon-carbon composite material is filled with pores by gas deposition method, which greatly improves the problems of high specific surface area, low initial efficiency and low conductivity of porous silicon.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a low-expansion porous silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] Silicon-carbon composite materials hold promise as a next-generation anode material for applications requiring high energy density. The most typical structure of silicon-carbon composites is the coating structure. Simply put, by coating the surface of the active material silicon with a carbon layer, direct contact between silicon particles and the electrolyte is prevented, mitigating the volume effect of silicon and enhancing its conductivity. Based on the coating structure and silicon particle morphology, common coating structures include core-shell, yolk-shell, and porous types.

[0003] Porous silicon possesses an abundant pore structure. Compared to conventional nano-silicon particles, the internal voids in silicon provide a buffer space for material expansion, alleviating internal mechanical stress. Simultaneously, the pore structure offers rapid ion transport channels, resulting in better electrical properties. However, porous silicon has a large specific surface area, leading to processing difficulties and increasing the risk of direct contact between silicon particles and the electrolyte. This can cause excessive lithium ion consumption, forming an SEI film and resulting in lower first-pass efficiency. Furthermore, silicon's intrinsic conductivity is low, leading to poor electron conduction.

[0004] To address the aforementioned issues, the solution involves constructing an artificial SEI film on the porous silicon surface to reduce electrolyte consumption, mitigate irreversible capacity loss, and improve the material's coulombic efficiency. Chinese patent CN117673287A describes a method where porous silicon is nano-sized, granulated, and then uniformly mixed with lithium powder, dispersant, carbon source, etc., followed by calcination. This pre-lithiation treatment and coating of the porous silicon surface effectively improves the initial coulombic efficiency and cycle stability of lithium batteries. However, the solid-phase mixing method easily leads to uneven dispersion, making it difficult for the material to penetrate the porous silicon pores. This results in an unevenly formed SEI film, ultimately affecting the material's electrochemical performance.

[0005] Carbon nanotubes are one-dimensional carbon nanomaterials characterized by good toughness and high electrical conductivity. Combining carbon nanotubes with porous silicon-carbon materials improves the material's conductivity and enhances its electrochemical performance. Chinese patent CN106058256A describes a method that uses a porous silicon matrix loaded with a metal catalyst to distribute carbon nanotubes both inside and outside the porous silicon particles via chemical vapor deposition (CVD). This enhances the overall electronic conductivity of the porous silicon, effectively increasing the reversible capacity of the silicon anode material and improving its electrochemical performance. However, the deposition of carbon nanotubes on the porous silicon surface via CVD suffers from poor surface uniformity and weak adhesion between the carbon nanotubes and the silicon surface, making them prone to detachment during charge-discharge cycles. Furthermore, the porous silicon pores are difficult to fill, posing a risk of direct contact with the electrolyte, resulting in low initial efficiency and rapid degradation of cycle performance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a silicon-carbon composite material in which a uniform SEI film is formed in the pores of porous silicon, carbon nanotubes are embedded inside the porous silicon particles, and then carbon is coated. Another purpose of this invention is to provide a low-expansion porous silicon-carbon composite material with high initial efficiency, high conductivity, and long cycle life.

[0007] This invention discloses a method for preparing a low-expansion porous silicon-carbon composite material, comprising the following steps:

[0008] S1 Preparation of Functionalized Porous Silicon: Silicon-aluminum alloy is reacted in acid to obtain porous silicon, and the porous silicon is washed with water until neutral; then, a mixed solution of concentrated sulfuric acid and hydrogen peroxide is added and stirred until the surface of the porous silicon is hydroxylated, washed with water, and dried to obtain functionalized porous silicon;

[0009] S2 Pre-lithiation of the surface of functionalized porous silicon: The functionalized porous silicon obtained in step S1 is uniformly dispersed in water to form a uniform suspension. The suspension is mixed with an aqueous solution of lithium acetate and allowed to react fully. Then, an aqueous solution of ammonium fluoride is added and stirred until the reaction is complete to obtain a mixture.

[0010] S3 Preparation of spray-dried precursor: The mixture obtained in step S2 is mixed evenly with the carbon nanotube dispersion; then mixed with the first carbon source dispersion to form a uniform and stable precursor liquid;

[0011] S4 Spray drying: The precursor liquid obtained in step S3 is spray dried to obtain powder;

[0012] S5 High-temperature carbonization and second carbon source filling: The powder obtained in step S4 is carbonized at high temperature in a protective gas atmosphere, and then a second carbon source is introduced to perform vapor deposition filling of the composite material, followed by cooling and sieving.

[0013] Aluminum is removed from the silicon-aluminum alloy using an acid solution to form porous silicon. The porous silicon is then added to a mixed solution of concentrated sulfuric acid and hydrogen peroxide to hydroxylate its surface. The hydroxyl groups on the surface of the hydroxylated porous silicon coordinate or chemically bond with lithium ions. Upon the addition of ammonium fluoride, the lithium ions combine with fluoride ions, forming a uniform LiF layer on the surface of the porous silicon and its pores through liquid-phase deposition.

[0014] Furthermore, in step S1, the particle size of the silicon-aluminum alloy is 50-300 nm, and the mass ratio of silicon to aluminum is 1:1-5; the acid solution is selected from hydrochloric acid and sulfuric acid, with a concentration of 10-30 wt%; the reaction time is 6-24 h; the mass ratio of concentrated sulfuric acid to hydrogen peroxide is 1-3:1, and the reaction time is 0.5-2 h.

[0015] Furthermore, in step S2, the content of functionalized porous silicon in the suspension is 10-30 wt%; the concentrations of the lithium acetate aqueous solution and the ammonium fluoride aqueous solution are both 5-20 wt%, and the molar ratio of lithium acetate to ammonium fluoride added is 1:1.

[0016] Furthermore, in step S2, the content of porous silicon in the solid material of the obtained mixture is 60-90 wt%. A uniform LiF layer on the surface and in the pores of the silicon-carbon composite material simultaneously ensures the optimal performance of the silicon-carbon alloy.

[0017] The solid material in the mixture is porous silicon with LiF deposited on its surface, forming an artificial SEI film on the surface of the porous silicon.

[0018] Furthermore, in step S3, the carbon nanotubes have a diameter of 1-10 nm and a length of 0.5-2 μm; the concentration of carbon nanotubes in the carbon nanotube dispersion is 0.1-0.2 wt%; and the mass of the carbon nanotubes is 0.5-3% of the mass of the functionalized porous silicon.

[0019] By encapsulating carbon nanotubes with a primary carbon source, the bonding force between the carbon nanotubes and porous silicon is strengthened, making them less likely to detach during cycling.

[0020] Furthermore, in step S3, the dispersion solvents used to disperse the carbon nanotubes and the first carbon source are each independently selected from one or more of acetone, isopropanol, toluene, heavy oil, tetrahydrofuran, and water.

[0021] Furthermore, in step S3, the first carbon source is selected from one or more of coal-based pitch, petroleum pitch, phenolic resin, furfural resin, and polyethylene glycol; the mass of the first carbon source is 1-10% of the mass of the functionalized porous silicon.

[0022] Furthermore, in step S4, during the spray drying operation, the inlet temperature is 110-150℃, the feed rate is 0.1-5L / h, and the particle size of the powder is controlled at 3-15μm.

[0023] Furthermore, in step S5, the high-temperature carbonization temperature is 800-1200℃, the heating rate is 5-20℃ / min, and the holding time is 1-2h; the second carbon source is selected from methane, ethane, propane, and acetylene; the flow rate of the second carbon source is 0.5-3L / min, and the introduction time is 1-5h.

[0024] Furthermore, in step S5, a rotary kiln is used for high-temperature carbonization; wherein the rotation speed of the rotary kiln is 0.3-1.5 r / min.

[0025] Furthermore, in step S5, the mesh size of the sieve used for sieving is 200-350 mesh.

[0026] Carbon is filled into the pores of the carbonized porous silicon carbon through vapor deposition. This avoids direct contact between the electrolyte and the porous silicon.

[0027] The present invention also discloses a low-expansion porous carbon composite material, which is prepared by the preparation method described above.

[0028] The present invention also discloses a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode comprises a low-expansion porous silicon-carbon composite material as described above, with an initial efficiency greater than 90%.

[0029] The low-expansion porous silicon-carbon composite material provided by this invention anchors lithium ions on the functionalized porous silicon surface, and then uses liquid-phase precipitation reaction to generate an artificial SEI film in situ in the pores and surface of the porous silicon, solving the problem of uneven SEI film growth; carbon nanotubes are embedded between porous silicon particles, and a first carbon source binds the porous silicon and carbon nanotubes together, and the porous silicon-carbon composite material is filled with vapor phase deposition, which greatly improves the problems of high specific surface area, low initial efficiency, and low conductivity of porous silicon. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation method of the low-expansion porous carbon composite material disclosed in this invention;

[0031] Figure 2 This is a schematic diagram of the structure of the low-expansion porous carbon composite material disclosed in this invention;

[0032] Figure 3 This is the XRD pattern of the low-expansion porous silicon-carbon composite material of Example 1 in this invention;

[0033] Figure 4 These are the powder resistance test results of Example 1 and Comparative Examples 1-2 in this invention;

[0034] Figure 5 This is a coin cell capacity test diagram of the low-expansion porous silicon-carbon composite material in Example 1 of this invention;

[0035] Figure 6 These are tethered cycling test diagrams of the porous silicon-carbon composite materials of Example 1 and Comparative Examples 1 and 2 in this invention. Detailed Implementation

[0036] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] Preparation of low-expansion porous silicon-carbon composite materials:

[0039] S1: Take 10g of 100nm silicon-aluminum alloy (silicon-aluminum mass ratio of 1:2) and place it in 100mL of 25wt% H2SO4 solution. Stir for 12h and wash with water until neutral. Then slowly add it to 100mL of 98% concentrated H2SO4 and 30% H2O2 (mass ratio of 5:2) and treat for 1h. After washing with water until neutral, dry under vacuum at 80℃ to obtain hydroxylated porous silicon powder.

[0040] S2: The hydroxylated porous silica powder obtained in step S1 was added to deionized water to prepare a 10wt% suspension. The suspension was ultrasonically dispersed and then 29g of 10wt% lithium acetate aqueous solution was added. After stirring for 2 hours, 16g of 10wt% NH4F aqueous solution was slowly added dropwise. Stirring was continued for 1 hour to obtain a mixed solution (the solid material of the mixed solution contains 90wt% porous silica and 10wt% LiF).

[0041] S3: Slowly add 100g of 0.1wt% carbon nanotube dispersion (carbon nanotube diameter 5nm, length 0.8μm, dispersant is water) to the mixture, stir evenly, then add 40g of 0.5wt% isopropanol dispersion of phenolic resin, and continue stirring until a uniform and stable precursor liquid is formed.

[0042] S4: Atomize and dry the precursor liquid at an inlet temperature of 120℃ and a feed rate of 1L / h. The particle size D50 of the obtained dry powder is controlled at 7-8μm.

[0043] S5: Place the dry powder in a rotary kiln, introduce argon gas, and rotate the rotary kiln at 0.5 r / min. First, heat the powder to 900℃, hold it for 2 hours, and then introduce acetylene (flow rate 1 L / min) for 1 hour. Then, cool the powder and pass it through a 300-mesh sieve to obtain a low-expansion porous silicon-carbon composite material.

[0044] Example 2

[0045] Preparation of low-expansion porous silicon-carbon composite materials:

[0046] S1: 10g of 150nm silicon-aluminum alloy (silicon-aluminum mass ratio of 1:2) was placed in 100mL of 25wt% HCl solution and stirred for 12h. After washing with water until neutral, it was slowly added to 100mL of 98% concentrated H2SO4 and 30% H2O2 (mass ratio of 7:3) and treated for 0.5h. After washing with water until neutral, it was dried under vacuum at 80℃ to obtain hydroxylated porous silicon powder.

[0047] S2: The hydroxylated porous silica powder obtained in step S1 was added to deionized water to prepare a 12wt% suspension. The suspension was ultrasonically dispersed and then 29g of 10wt% lithium acetate aqueous solution was added. After stirring for 2 hours, 16g of 10wt% NH4F solution was slowly added dropwise and stirring was continued for 1 hour to obtain a mixed solution (the solid material of the mixed solution contains 90wt% porous silica and 10wt% LiF).

[0048] S3: Slowly add 27g of 0.3wt% carbon nanotube dispersion (carbon nanotube diameter 3nm, length 1μm, dispersion solvent is water) to the mixture, stir evenly, then add 40g of 0.5wt% isopropanol dispersion of petroleum asphalt, and continue stirring until a uniform and stable precursor liquid is formed.

[0049] S4: Spray dry the precursor liquid at an inlet temperature of 110℃ and a feed rate of 1.2L / h, and control the particle size D50 of the obtained dry powder to be 7-8μm.

[0050] S5: Place the dry powder in a rotary kiln, introduce argon gas, and rotate the rotary kiln at 0.3 r / min. First, heat the powder to 850℃, hold it at that temperature for 2 hours, and then introduce acetylene (flow rate 1 L / min) for 1.5 hours. Then, cool the powder and pass it through a 300-mesh sieve to obtain a low-expansion porous silicon-carbon composite material.

[0051] Example 3

[0052] Preparation of low-expansion porous silicon-carbon composite materials:

[0053] S1: 12g of 100nm silicon-aluminum alloy (silicon-aluminum mass ratio of 1:2.5) was placed in 100mL of 20% H2SO4 solution and stirred for 15h. After washing with water until neutral, it was slowly added to 100mL of 98wt% concentrated H2SO4 and 30wt% H2O2 (mass ratio of 7:3) and treated for 1h. After washing with water until neutral, it was dried under vacuum at 80℃ to obtain hydroxylated porous silicon powder.

[0054] S2: Hydroxylated porous silica powder was added to deionized water to prepare an 8wt% suspension, which was ultrasonically dispersed evenly. 19g of 15wt% lithium acetate solution was added, and the mixture was stirred for 1.5h. Then, 10.5g of 15wt% NH4F solution was slowly added dropwise, and the mixture was stirred for another 1h to obtain a mixed solution (the solid material in the mixed solution contained 88wt% porous silica and 12wt% LiF).

[0055] S3: Slowly add 150g of 0.1wt% carbon nanotube dispersion (carbon nanotube diameter 4nm, length 1μm, dispersion solvent is water, carbon nanotubes are porous silicon with mass 1.5wt%) to the mixture, stir evenly, then add 30g of 1wt% ethanol dispersion of phenolic resin, and continue stirring until a uniform and stable precursor liquid is formed.

[0056] S4: Spray dry the precursor liquid at an inlet temperature of 120℃ and a feed rate of 0.8L / h, and control the particle size D50 of the obtained dry powder to be 7-8μm.

[0057] S5: Place the dry powder in a rotary kiln, introduce argon gas, and rotate the rotary kiln at 0.3 r / min. First, heat the powder to 950℃ and hold it for 2 hours. Then, introduce acetylene (flow rate 1 L / min) for 0.5 hours. Cool the powder and pass it through a 300-mesh sieve to obtain a low-expansion porous silicon-carbon composite material.

[0058] like Figure 1-2 As shown, an artificial SEI film (LiF) is formed by in-situ reaction on the surface of porous silicon particles and the surface of pores. The first carbon source binds the porous silicon particles to carbon nanotubes, and secondary particles are formed by spray drying. After carbonization, the secondary particles are filled with pores by vapor deposition.

[0059] Comparative Example 1

[0060] Preparation of silicon-carbon composite materials:

[0061] 1) Take 10g of 100nm silicon-aluminum alloy (silicon-aluminum mass ratio of 1:2) and place it in 100mL of 25wt% H2SO4 solution. Stir for 12h and wash with water until neutral. Then slowly add it to 100mL of 98wt% concentrated H2SO4 and 30% H2O2 (mass ratio of 5:2) and treat for 1h. After washing with water until neutral, dry under vacuum at 80℃ to obtain hydroxylated porous silicon powder.

[0062] 2) Prepare a 10% emulsion of hydroxylated porous silica powder, disperse it evenly by ultrasonication, slowly add 100g of 0.1% carbon nanotube dispersion (carbon nanotube diameter 5nm, length 0.8μm, dispersion solvent is water), stir evenly, add 40g of 0.5wt% isopropanol dispersion of phenolic resin, and continue stirring until a uniform and stable precursor liquid is formed.

[0063] 4) Spray dry the precursor liquid at an inlet temperature of 120℃ and a feed rate of 1L / h. The particle size D50 of the resulting dry powder is controlled at 7-8μm.

[0064] 5) Place the dry powder in a rotary kiln, introduce argon gas, and rotate the rotary kiln at 0.5 r / min. First, heat the powder to 900℃, keep it at that temperature for 2 hours, and then introduce acetylene (flow rate 1 L / min) for 1 hour. Cool the powder and pass it through a 300-mesh sieve to obtain a porous silicon-carbon composite material.

[0065] Comparative Example 2

[0066] Preparation of silicon-carbon composite materials:

[0067] 1) Take 10g of 100nm silicon-aluminum alloy (silicon-aluminum mass ratio of 1:2) and place it in 100mL of 25wt% H2SO4 solution. Stir for 12h and wash with water until neutral. Then slowly add it to 100mL of 98wt% concentrated H2SO4 and 30wt% H2O2 (mass ratio of 5:2) and treat for 1h. After washing with water until neutral, dry under vacuum at 80℃ to obtain hydroxylated porous silicon powder.

[0068] 2) Hydroxylated porous silica powder was added to deionized water to prepare a 10wt% suspension, which was ultrasonically dispersed evenly. 29g of 10wt% lithium acetate solution was added and stirred for 2h. Then, 16g of 10wt% NH4F solution was slowly added dropwise and stirred for another 1h to obtain a mixed solution (the solid material of the mixed solution contained 90wt% porous silica and 10wt% LiF).

[0069] 3) Add 40g of 0.5% isopropanol dispersion of phenolic resin (phenolic resin is 2% of the porous silica mass) to the mixture and continue stirring until a uniform and stable precursor liquid is formed.

[0070] 4) Spray dry the precursor liquid at an inlet temperature of 120℃ and a feed rate of 1L / h. The particle size D50 of the resulting dry powder is controlled at 7-8μm.

[0071] 5) Place the dry powder in a rotary kiln, introduce argon gas, and rotate the rotary kiln at 0.5 r / min. First, heat the powder to 900℃, keep it at that temperature for 2 hours, and then introduce acetylene (flow rate 1 L / min) for 1 hour. Cool the powder and pass it through a 300-mesh sieve to obtain a porous silicon-carbon composite material.

[0072] Performance testing:

[0073] The low-expansion porous silicon-carbon composite material obtained in Example 1 was subjected to X-ray powder diffraction testing, and the results are as follows: Figure 3 As shown.

[0074] The porous silicon-carbon composite materials prepared in Example 1 and Comparative Examples 1-2 were subjected to powder resistivity testing. The test results are as follows: Figure 4 As shown.

[0075] The porous silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were used to fabricate 2032 button batteries for evaluation. Specifically, the materials, conductive agent SP, conductive agent VGCF, and binder LA136 were mixed in a mass ratio of 75:5:10:10. Water was used as the solvent, and the slurry was coated onto copper foil. The counter electrode was a lithium sheet, and the separator was a Celgard 2400 microporous polypropylene membrane. The charge / discharge cutoff voltage was 0.005-1.5V. The discharge rate was first 0.1C to 0.005V, then 0.02C to 0.005V to ensure complete discharge. The charging rate was 0.1C to 1.5V. The test results for various performance parameters are shown in Table 1.

[0076] Table 1. Results of button battery tests in Examples 1-4 and Comparative Examples 1-2

[0077] Material Electrode resistance (Ω) Electrode swelling rate (%) Initial lithium insertion capacity (mAh / g) Initial delithiation capacity (mAh / g) First-time efficiency (%) Example 1 0.010 15.3 2110 1942.4 92.06 Example 2 0.011 14.8 2076.2 1894.7 91.26 Example 3 0.011 14.5 2067.8 1900 91.88 Comparative Example 1 0.012 20.4 2018.3 1702.6 84.34 Comparative Example 2 0.021 18.6 2039.6 1828.5 89.65

[0078] Results analysis:

[0079] from Figure 3 It can be seen that the low-expansion porous silicon-carbon composite material prepared in Example 1 mainly exhibits a crystalline silicon structure.

[0080] like Figure 4 As shown, Example 1 has a lower resistivity compared to Comparative Examples 1-2, and the resistivity reduction in Example 1 is more significant compared to Comparative Example 2. This demonstrates that adding carbon nanotubes between porous silicon particles can greatly improve the conductivity of silicon-carbon composite materials.

[0081] like Figure 5 As shown, Example 1 exhibits a high initial lithium insertion / extraction capacity, with a lithium extraction capacity of 1942.4 mAh / g at 1.5V and an initial efficiency of 92.06%.

[0082] like Figure 6 As shown, compared with Comparative Examples 1-2, the capacity retention rate of Example 1 is significantly improved.

[0083] As shown in Table 1, compared with Comparative Examples 1-2, the electrode swelling rate of Examples 1-3 was greatly reduced, and the initial lithium insertion capacity, initial lithium extraction capacity and initial efficiency were greatly improved.

[0084] Although the electrode resistance of Comparative Example 1 is not much different from that of Example 1, the electrode swelling rate, initial lithium insertion capacity, initial lithium extraction capacity and initial efficiency are significantly worse because Comparative Example 1 did not deposit LiF on the surface of porous carbon and pores.

[0085] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a low-expansion porous silicon-carbon composite material, characterized in that, Includes the following steps: S1 Preparation of Functionalized Porous Silicon: Silicon-aluminum alloy is reacted in acid to obtain porous silicon, and the porous silicon is washed with water until neutral; then, a mixed solution of concentrated sulfuric acid and hydrogen peroxide is added and stirred until the surface of the porous silicon is hydroxylated, washed with water, and dried to obtain functionalized porous silicon; S2 Pre-lithiation of the surface of functionalized porous silicon: The functionalized porous silicon obtained in step S1 is uniformly dispersed in water to form a uniform suspension. The suspension is mixed with an aqueous solution of lithium acetate and allowed to react fully. Then, an aqueous solution of ammonium fluoride is added and stirred until the reaction is complete to obtain a mixture. S3 Preparation of spray-dried precursor: The mixture obtained in step S2 is mixed evenly with the carbon nanotube dispersion; then mixed with the first carbon source dispersion to form a uniform and stable precursor liquid; S4 Spray drying: The precursor liquid obtained in step S3 is spray dried to obtain powder; S5 High-temperature carbonization and second carbon source filling: The powder obtained in step S4 is carbonized at high temperature in a protective gas atmosphere, and then a second carbon source is introduced to perform vapor deposition filling of the composite material, followed by cooling and sieving. In step S1, the particle size of the silicon-aluminum alloy is 50-300 nm, and the mass ratio of silicon to aluminum is 1:1-5; the acid solution is selected from hydrochloric acid and sulfuric acid, and the concentration is 10-30 wt%; the reaction time is 6-24 h; the mass ratio of concentrated sulfuric acid to hydrogen peroxide is 1-3:1, and the reaction time is 0.5-2 h. In step S2, the content of functionalized porous silicon in the suspension is 10-30 wt%; the concentrations of the lithium acetate aqueous solution and the ammonium fluoride aqueous solution are both 5-20 wt%, and the molar ratio of lithium acetate to ammonium fluoride added is 1:

1. In step S3, the concentration of carbon nanotubes in the carbon nanotube dispersion is 0.1-0.2 wt%; the diameter of the carbon nanotubes is 1-10 nm and the length is 0.5-2 μm; the mass of the carbon nanotubes is 0.5-3% of the mass of the functionalized porous silicon.

2. The method for preparing a low-expansion porous silicon-carbon composite material according to claim 1, characterized in that, The In step S3, the dispersion solvents used to disperse the carbon nanotubes and the first carbon source are each independently selected from one or more of acetone, isopropanol, toluene, heavy oil, tetrahydrofuran, and water.

3. The method for preparing a low-expansion porous silicon-carbon composite material according to claim 2, characterized in that, In step S3, the first carbon source is selected from one or more of coal-based pitch, petroleum pitch, phenolic resin, furfural resin, and polyethylene glycol; the mass of the first carbon source is 1-10% of the mass of the functionalized porous silicon.

4. The method for preparing a low-expansion porous silicon-carbon composite material according to claim 1, characterized in that, In step S4, during the spray drying operation, the inlet temperature is 110-150℃, the feed rate is 0.1-5L / h, and the particle size of the powder is controlled at 3-15μm.

5. The method for preparing a low-expansion porous silicon-carbon composite material according to claim 1, characterized in that, In step S5, the high-temperature carbonization temperature is 800-1200℃, the heating rate is 5-20℃ / min, and the holding time is 1-2h; the second carbon source is selected from methane, ethane, propane, and acetylene; the flow rate of the second carbon source is 0.5-3L / min, and the introduction time is 1-5h.

6. A low-expansion porous silicon-carbon composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes the low-expansion porous silicon-carbon composite material as described in claim 6, with an initial efficiency greater than 90%.

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