Silicon-carbon composite negative electrode material and preparation method therefor

Abstract

The present invention provides a silicon-carbon composite negative electrode material and a preparation method therefor. The silicon-carbon composite negative electrode material is obtained by depositing silicon-containing particles on pores and surfaces of porous carbon, and then performing surface carbon coating. In an XPS Si 2p spectrum of the silicon-carbon composite negative electrode material, the surface of the material satisfies: 0.4<SSi-Si / SC-Si-O<0.7; and the interior satisfies: 3<SSi-C / SC-Si-O<4. The surface of the material refers to the XPS spectrum measured when the material has not been etched by an argon ion beam, and the interior of the material refers to the XPS spectrum measured after the material has been etched by an argon ion beam to a depth of 70nm. A material having the specified XPS Si 2p spectrum has significantly improved structural strength, capacity and conductivity, thereby improving cycle stability and fast charging performance, and achieving high energy density, for a lithium ion battery assembled using same.

Description

A silicon-carbon composite anode material and its preparation method Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a silicon-carbon composite anode material and its preparation method. Background Technology

[0002] With the expansion of the new energy sector and the development of lithium-ion batteries, the shift in demand and production from gigawatt-hours (GWh) to terawatt-hours (TWh) has had a significant impact on the industry, as well as on technological development and battery requirements. For example, there is a growing demand for battery sustainability. Since lithium-ion batteries are widely used in electric vehicles, factors such as high energy density and driving range are particularly important and have become targets for optimizing battery performance to significantly improve energy density parameters. In industry roadmaps, targets exceeding 800 Wh / kg and 350 Wh / kg are not uncommon. To achieve these goals, the industry is turning to high-nickel cathodes, silicon anodes, and new battery and battery pack designs, with anode materials being of paramount importance.

[0003] A good anode material must be stable and allow for as many lithium insertions and extractions as possible to maximize the battery's energy density, power density, and cycle life. For high-power applications, low resistance and fast lithium-ion transport within the anode material are also essential. The modern lithium-ion battery industry primarily uses graphite. To retain a limited amount of lithium within the encapsulated battery, high-performance lithium batteries require the formation of a robust solid electrolyte interphase (SEI) film and minimizing irreversible lithium compounds on the anode. Lithium ions are "stored" in graphite anode materials through intercalation into layered carbons such as graphite, adsorption on hard carbon, and bonding with hydrogen atoms in hydride carbon. Mesophase carbon microspheres (MCMBs) possess a high theoretical capacity of 372 mA h / g and a low potential distribution (0-0.3 V vs. Li / Li). + MCMB has become the standard anode material for modern commercial lithium-ion batteries. However, its specific capacity is insufficient for demanding applications. Materials such as Sn, Sb, Si, and Ge "store" charge by reacting with lithium to form alloys. Among them, silicon has a theoretical specific capacity much higher than MCMB and other anode materials, approximately 4200 mAh / g (Li). 4.4 Si).

[0004] However, when silicon-lithium alloys are formed, the volume of silicon expands by 380%. This expansion and contraction of silicon causes irreversible mechanical damage to the silicon-based electrode. The silicon powder loses electrical contact with the current collector, preventing electrons from transferring from silicon to the current collector. This charge balance restricts the movement of positively charged lithium ions from silicon to the cathode, thus losing charge-discharge capability. Furthermore, new electrolyte interphase (SEI) grows on the new surface formed by silicon breakage, consuming additional lithium. When the lithium in the battery is depleted to a low level, the battery fails. Therefore, maintaining electrical contact between silicon particles and the current collector, and reducing the amount of irreversible SEI by minimizing the amount of fresh silicon surface in contact with the electrolyte, presents a challenge. To address this, a new generation of silicon-based anode materials has been developed, which involves depositing nano-silicon into a porous carbon substrate. The porous carbon framework enhances the conductivity of silicon, while the confinement effect of the nano-silicon and nanopores buffers the volume expansion of the silicon particles. Summary of the Invention

[0005] To address the need for further improvement in the electrochemical performance of existing silicon-carbon composite anode materials, this invention provides a novel silicon-carbon composite material and its preparation method. A porous carbon material is formed by activating and pore-forming a carbon material containing at least one of disordered carbon, microcrystalline carbon, or crystalline carbon, achieving a specific gravity of 2000-4000 μm. 2 / g. A silicon-carbon composite material is formed by depositing silicon onto the interface of a porous carbon material. The silicon deposition on the carbon framework provides superior conductivity and buffers volume expansion, improving cycle stability. The silicon-carbon composite material provided by this invention is characterized by XPS: the surface is composed of materials containing Si, Si-O, and C-Si-O groups, while the interior is mainly composed of materials containing Si-C groups. To achieve the above objectives, this invention provides the following technical solution:

[0006] A silicon-carbon composite anode material is obtained by depositing silicon-containing particles on the pores and surface of porous carbon, followed by surface carbon coating. The XPS Si 2p spectrum of this silicon-carbon composite anode material shows a surface area of ​​0.4... Si-Si / S C-Si-O <0.7, material inside: 3 Si-C / S C-Si-O <4; where the material surface refers to the XPS spectrum measured without argon ion beam etching, and the material interior refers to the XPS spectrum measured after argon ion beam etching to a depth of 70 nm; S Si-Si The area of ​​the Si 2p fractionation peak near 98±0.5 eV is represented by S. C-Si-O The area of ​​the Si 2p fractionation near 102±0.5 eV, S Si-C The area of ​​the Si 2p peak near 101.5±0.5 eV.

[0007] ​​The inventors unexpectedly discovered that materials with the aforementioned specific XPS-like Si 2p spectra exhibit significantly improved structural strength, capacity utilization, and conductivity, thereby enhancing the cycle stability, fast-charging performance, and achieving high energy density in lithium-ion batteries assembled using them. A possible reason for this is that when the surface S... Si-Si / S C-Si-O When the surface silicon content is less than 0.4, the presence of more silicon oxide on the surface leads to lower capacity and poorer conductivity; when the surface silicon content is less than 0.4, the presence of more silicon oxide on the surface leads to lower capacity and poorer conductivity. Si-Si / S C-Si-O When the S content is greater than 0.7, on the one hand, over-deposition leads to low internal porosity of silicon-carbon, which cannot effectively buffer volume expansion, resulting in poor cycling performance. On the other hand, the presence of large elemental silicon particles leads to poor interfacial stability and easy expansion and breakage during cycling, exhibiting poor cycling stability. Si-C / S C-Si-O When the silicon content is less than 3, the silicon deposition uniformity is poor, and pore blockage occurs, preventing deposition into the porous carbon interior; when the internal S... Si-C / S C-Si-O When the value is greater than 7, more SiC is generated, resulting in poor capacity utilization.

[0008] Furthermore, the specific surface area of ​​the porous carbon is 2000-4000 m². 2 / g, pore volume 0.9-1.2cm³ 3 / g. In a preferred embodiment of the present invention, the porous carbon is prepared by carbon source pyrolysis followed by activation. The activation is a two-stage activation: the primary activation is steam activation, and the secondary activation is carbon dioxide or metal hydroxide activation (potassium hydroxide and / or sodium hydroxide).

[0009] Preferably, the primary activation is performed using steam at 800-950℃, resulting in a pore volume of 0.5-0.7 cm³ after primary activation. 3 / g; In the secondary activation, carbon dioxide is used as the activating agent, and the activation temperature is 900-1000℃; during metal hydroxide activation, the activation temperature is 700-900℃; after secondary activation, the pore volume of the obtained porous carbon is 0.9-1.2 cm³. 3 / g

[0010] Furthermore, in the silicon-carbon composite anode material, the Si mass percentage is 40-65 wt%, and the carbon coating thickness is 2-10 nm.

[0011] The deposition of silicon-containing particles and carbon coating processes are well known in the art. For example, silicon deposition involves one or more methods such as vapor deposition, vapor infiltration, ALD, electroplating, melt infiltration, sol-gel, and impregnation to uniformly deposit silicon-containing particles onto the interface of carbon materials. These silicon-containing particles contain silicon, oxygen, and carbon, primarily elemental silicon, but also exhibiting chemical bonds between silicon and carbon, as well as between silicon and oxygen. Vapor deposition is preferred, where a silicon-containing source gas is treated at a specific temperature to decompose and generate silicon nanoparticles that are adsorbed into the porous carbon channels, achieving amorphous nanocrystalline silicon deposition with a silicon deposition amount to porous carbon substrate mass ratio close to 1:1.

[0012] The carbon coating process involves pyrolyzing a carbon-containing gas under an inert atmosphere, resulting in the deposition of a dense carbon layer on the material surface. The carbon-containing process gas is selected from at least one of methane, ethane, propane, butane, ethylene, propylene, butene, butadiene, acetylene, and propyne. The carbon coating temperature is 500-600℃; the thickness of the carbon coating layer is 3-10 nm.

[0013] This invention also provides a method for preparing the above-mentioned silicon-carbon composite anode material, comprising the following steps:

[0014] (S1) Pretreatment: In a vapor deposition equipment, the porous carbon is pretreated at 900-1000℃ by introducing carbon source gas; the porous carbon is obtained by pore formation by carbon source through two activations, the first activation is water vapor activation, and the second activation is carbon dioxide activation or metal hydroxide activation.

[0015] (S2) Primary silicon deposition: Cool down to 450-500℃, introduce a mixture of silane and inert gas, and control the amount of gas introduced so that the amount of silicon deposited accounts for 10-15 wt% of the product.

[0016] (S3) Secondary silicon deposition: Heat to 550-650℃, continue to introduce a mixture of silane and inert gas, and continue silicon deposition. Control the gas flow rate so that the amount of silicon deposited accounts for 40-65 wt% of the product.

[0017] (S4) Carbon coating: Cool down to 500-600℃ and introduce carbon-containing process gas for carbon coating.

[0018] Furthermore, in step (S1), the carbon source gas is a C1-3 alkane. The carbon source gas has small molecules that are easy to enter the pores and deposit along the interface. By controlling the carbon source introduction rate to 1-2 L / min and the pretreatment time to 1-2 h, it is deposited onto the pore walls of the porous carbon without clogging the pores, thereby achieving graphene surface treatment of the internal carbon walls. Since there are more defects and dangling bonds on the graphene surface, it is easier to adsorb silane gas, thus making heterogeneous deposition of silicon greater than homogeneous deposition in the subsequent deposition process.

[0019] Further, in steps (S2) and (S3), the silicon source gas is selected from at least one of silane, silane, dichlorosilane, and chlorosilane; the inert gas is selected from at least one of nitrogen, argon, and helium.

[0020] Step (S2) involves low-temperature deposition to facilitate the deposition of silicon source gas into the porous carbon. Then, the temperature is increased to perform high-temperature deposition in step (S3) to improve silicon deposition utilization.

[0021] This invention achieves a surface area of ​​0.4 by controlling the deposition amount and carbon coating. Si-Si / S C-Si-O <0.7, achieved through pretreatment processes, deposition amount, and deposition temperature: 3 Si-C / S C-Si-O <4.

[0022] Furthermore, the porous carbon is obtained by activating the carbon source twice to create pores, followed by high-temperature recarbonization, specifically including the following steps:

[0023] (T1) The carbon source was activated once in the presence of water vapor, resulting in a pore volume of 0.5-0.7 cm³. 3 / g of the first porous carbon;

[0024] (T2) The first porous carbon undergoes secondary activation using carbon dioxide or metal hydroxides (sodium hydroxide and / or potassium hydroxide) as the activator, resulting in a pore volume of 0.9-1.2 cm³. 3 / g of the second porous carbon;

[0025] (T3) The second porous carbon is crushed and recarbonized in a high-temperature furnace to finally obtain porous carbon.

[0026] Further, in step (T1), the carbon source is formed by carbonizing one or more of coconut shell carbon, asphalt, petroleum coke and resin through pyrolysis, with the pyrolysis temperature being 700-1000℃; the steam activation temperature is 800-950℃.

[0027] Furthermore, in step (T2), when the activator is carbon dioxide, the activation temperature is 900-1000℃; when the activator is metal hydroxide, the activation temperature is 700-900℃. The purpose of secondary activation is to further create micropores on the basis of a larger pore size, thereby forming a secondary porous carbon material with a pore structure gradient. In the subsequent silicon deposition process, this can facilitate the permeation of silane gas and avoid poor uniformity of deposition inside and outside the particles due to insufficient silane permeation.

[0028] ​​Furthermore, in step (T1), the orifice volume is adjusted by regulating the activation gas flow rate and activation time; in step (T2), when the activator is carbon dioxide, the orifice volume is adjusted by adjusting the carbon dioxide gas flow rate and activation time; when the activator is metal hydroxide, the orifice volume is adjusted by adjusting the carbon-alkali ratio.

[0029] Further, in step (T3), the material is crushed to a Dv50 of 5-10 μm and then recarbonized at 1100-1600℃ in an inert atmosphere for 2-5 hours to remove oxygen functional groups from the surface of the porous carbon material and improve its structural strength and conductivity. Attached Figure Description

[0030] Figure 1 shows the voltage-specific capacity curve for the first cycle of Example 1;

[0031] Figure 2 shows the Si 2p peak spectrum analysis of XPS in Example 1. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0033] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0034] X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific ESCALab 250Xi, with depth profiling analysis (~7 nm min) using argon ion beam sputtering. -1 ).

[0035] Preparation Example 1

[0036] (T1) Coconut shell carbon was used as a carbon source and activated once at 800℃ in the presence of water vapor. The activation gas flow rate and activation time were controlled to obtain a pore volume of 0.6 cm³. 3 / g of the first porous carbon precursor;

[0037] (T2) The first porous carbon precursor was subjected to secondary activation at 1000℃ in the presence of carbon dioxide. The activation gas flow rate and activation time were adjusted to obtain a pore volume of 1.1 cm³. 3 / g of the second porous carbon precursor;

[0038] (T3) The second porous carbon precursor was crushed to a Dv50 of 8 μm, and then heat-treated in a high-temperature furnace at 1400℃ for 2 hours under a nitrogen atmosphere to undergo recarbonization, finally obtaining porous carbon.

[0039] Preparation Example 2

[0040] Other conditions were the same as in Preparation Example 1, except that step (T2) was changed to: after mixing the first porous carbon precursor and potassium hydroxide, a secondary activation was performed at 800°C to adjust the carbon-base ratio, resulting in a pore volume of 1.1 cm³. 3 / g of the second porous carbon precursor.

[0041] Comparative Preparation Example 1

[0042] (T1) Coconut shell carbon was used as a carbon source and activated once at 800℃ in the presence of water vapor. The activation gas flow rate and activation time were controlled to obtain a pore volume of 1.1 cm³. 3 / g porous carbon precursor;

[0043] (T2) The porous carbon precursor was broken down to a Dv50 of 8 μm and then heat-treated in a high-temperature furnace at 1400 °C for 2 h under a nitrogen atmosphere to undergo recarbonization, finally obtaining porous carbon. That is, compared with preparation example 1, the carbon dioxide activation in step (T2) was eliminated.

[0044] Comparative Preparation Example 2

[0045] (T1) Coconut shell carbon was used as a carbon source and underwent secondary activation at 1000℃ in the presence of carbon dioxide. The activation gas flow rate and activation time were adjusted to obtain a pore volume of 1.1 cm³. 3 / g porous carbon precursor;

[0046] (T32) The porous carbon precursor was broken down to a Dv50 of 8 μm, and then heat-treated in a high-temperature furnace at 1400 °C for 2 h under a nitrogen atmosphere to undergo recarbonization, finally obtaining porous carbon. That is, compared with preparation example 1, the steam activation in step (T1) was eliminated.

[0047] Example 1

[0048] (S1) Take 10 kg of the porous carbon material prepared in Example 1 and put it into a vertical fluidized bed reactor. Introduce methane gas at 2 L / min at 950 °C and keep it at that temperature for 1 h.

[0049] (S2) After cooling to 450℃, a mixture of 5L / min silane gas and 5L / min nitrogen gas is introduced and kept at this temperature for 4 hours. Then the gas mixture is stopped. At this time, silicon accounts for 13.2wt% in the material obtained.

[0050] (S3) After heating to 550℃, continue to introduce a mixed gas of 5L / min silane and 5L / min nitrogen, and keep it at the temperature for 12h. At this time, silicon accounts for 51.5wt% in the obtained material.

[0051] (S4) The temperature was then raised to 600℃, acetylene gas was introduced at a rate of 5 L / min, and the temperature was maintained for 2 hours before being cooled to room temperature and discharged to obtain the silicon-carbon composite material. The prepared material was characterized by Si 2p testing using XPS, and the surface Si content was...Si-Si / S C-Si-O =0.63, internal material: S Si-C / S C-Si-O =3.2. The interior of the material is an XPS spectrum obtained by argon ion beam etching at a depth of 70 nm.

[0052] Figure 1 shows the first-cycle voltage-specific capacity curve of the silicon-carbon composite material prepared in Example 1.

[0053] Figure 2 shows the Si 2p peak spectrum analysis of the XPS of the silicon-carbon composite material prepared in Example 1.

[0054] Example 2

[0055] (S1) Take 10 kg of the porous carbon material prepared in Example 2 and put it into a vertical fluidized bed reactor. Introduce methane gas at 1 L / min at 900 °C and keep it at that temperature for 2 h.

[0056] (S2) After cooling to 500℃, a mixture of 5L / min silane gas and 5L / min nitrogen gas was introduced and kept at the temperature for 4 hours. Then the gas mixture was stopped. At this time, the silicon content in the material was 13.4wt%.

[0057] (S3) After heating to 650℃, a mixed gas of 5L / min silane and 5L / min nitrogen is continuously introduced and kept at the temperature for 12h. At this time, silicon accounts for 51.7wt% in the obtained material.

[0058] (S4) The temperature was then lowered to 550℃, methane gas was introduced at a rate of 5 L / min and held at this temperature for 4 hours, before being discharged to room temperature to obtain the silicon-carbon composite material. The final material was characterized by Si 2p testing using XPS, and the surface S... Si-Si / S C-Si-O The value is 0.59, and the internal S of the material is... Si-C / S C-Si-O It is 3.5.

[0059] Example 3

[0060] The other conditions and operations were the same as in Example 1, except that in step (S1), methane gas was replaced with ethylene, and the holding time was changed to 1.5 hours. The final material was characterized by Si 2p testing using XPS, and the surface Si... Si-Si / S C-Si-O The value is 0.45, and the internal S of the material is... Si-C / S C-Si-O It is 3.4.

[0061] Example 4

[0062] Other conditions and operations were the same as in Example 1, except that in step (S2), the holding time was changed to 5 hours, and the product obtained in step (S2) contained 14.7 wt% silicon. The final material was characterized by Si 2p testing using XPS, and the surface Si content was... Si-Si / S C-Si-O The value is 0.58, and the internal S of the material is... Si-C / S C-Si-O It is 3.3.

[0063] Example 5

[0064] The other conditions and operations were the same as in Example 1, except that in step (S3), the holding time was changed to 14 hours, and the product obtained in step (S2) contained 54.2 wt% silicon. The final material was characterized by Si 2p testing using XPS, and the surface Si content was... Si-Si / S C-Si-O The value is 0.70, and the internal S of the material is... Si-C / S C-Si-O It is 3.7.

[0065] Comparative Example 1

[0066] Other conditions and procedures were the same as in Example 1, except that in step (S1), the porous carbon was prepared in Comparative Preparation Example 1. The obtained material was characterized by XPS testing. The material surface showed: S... Si-Si / S C-Si-O The value is 0.84, and the internal composition of the material is S. Si-C / S C-Si-O It is 5.1.

[0067] Comparative Example 2

[0068] The other conditions and procedures were the same as in Example 1, except that in step (S1), the porous carbon was prepared in Comparative Preparation Example 2. The obtained material was characterized by XPS testing. The material surface showed: S... Si-Si / S C-Si-O The value is 0.54, and the internal composition of the material is S. Si-C / S C-Si-O It is 4.6.

[0069] Comparative Example 3

[0070] The other conditions and operations were the same as in Example 1, except that step (S1) was omitted, and the porous carbon material from Preparation Example 1 was used for steps (S2) to (S4). The final material was characterized by XPS testing, and the material surface showed: S Si-Si / S C-Si-O The value is 0.27, and the internal composition of the material is S. Si-C / S C-Si-O It is 2.8.

[0071] Comparative Example 4

[0072] Other conditions and operations were the same as in Example 1, except that the temperature was 400°C during the first silicon deposition in step (S2). The resulting material was characterized by XPS testing. The material surface showed: S Si-Si / S C-Si-O The value is 0.47, and the internal composition of the material is S. Si-C / S C-Si-O It is 2.6.

[0073] Comparative Example 5

[0074] Other conditions and operations were the same as in Example 1, except that the temperature was 500°C during the second silicon deposition in step (S3). The obtained material was characterized by XPS testing, and the material surface showed: S Si-Si / S C-Si-O The value is 0.78, and the internal composition of the material is S. Si-C / S C-Si-O It is 2.8.

[0075] Comparative Example 6

[0076] Other conditions and operations were the same as in Example 1, except that the temperature was 800°C during the second silicon deposition in step (S3). The obtained material was characterized by XPS testing, and the material surface showed: S Si-Si / S C-Si-O The value is 0.72, and the internal composition of the material is S. Si-C / S C-Si-O It is 4.1.

[0077] Comparative Example 7

[0078] Step (S1) is the same as in Example 1, followed by:

[0079] (S2) After cooling to 500℃, a mixture of 5L / min silane gas and 5L / min nitrogen gas was introduced and kept at this temperature for 16h. Then the gas mixture was stopped. At this point, silicon accounted for 52.4wt% of the material obtained.

[0080] (S3 was then heated to 600℃, acetylene gas was introduced at a rate of 5 L / min and held at that temperature for 2 hours, then cooled to room temperature and discharged to obtain the silicon-carbon composite material. The prepared material was characterized by Si 2p testing using XPS, and the surface Si...) Si-Si / S C-Si-O =0.77, Material internal: S Si-C / S C-Si-O =2.7.

[0081] Application examples

[0082] Performance testing of silicon-carbon composite materials as lithium battery anode materials

[0083] The silicon-based materials obtained in this invention were subjected to electrochemical performance testing according to the following method: silicon-carbon materials, Super P, carbon nanotubes, and carboxymethyl cellulose and styrene-butadiene rubber composite binder were mixed in a mass ratio of 80:9.8:0.2:10 to form a slurry (CMC and SBR mass ratio of 1:1). The slurry was coated onto copper foil with a 200 μm thick scraper, dried in a drying room, and then vacuum dried for 12 h to prepare a silicon-based negative electrode sheet. Then, lithium metal was used as the counter electrode, polyolefin as the separator, and 1 mol / L LiPF6 (solvent being a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) as the electrolyte. 2% VC and 5% FEC were added to the electrolyte. The cells were assembled into coin cells in an argon-atmosphere Braun inert gas glove box in Germany.

[0084] The assembled battery was subjected to charge-discharge tests on a LAND charge-discharge tester, with a charge-discharge range of 50mV to 1.5V and a compaction density of 1.1g / cm³. 3 After three charge-discharge cycles at a current density of 0.1C (1C = 1500 mA / g), a rate charge-discharge test was performed at a 1C rate.

[0085] Following the same method, the silicon-carbon composite materials obtained in the embodiments and comparative examples of the present invention were assembled into coin-type lithium batteries as negative electrode materials, and the electrochemical test results are listed in Table 1.

[0086] Table 1 Electrochemical performance test results of silicon-carbon composite materials

Claims

1. A silicon-carbon composite anode material, characterized in that, It is obtained by depositing silicon-containing particles on the pores and surface of porous carbon, followed by surface carbon coating. In the XPS Si 2p spectrum of the silicon-carbon composite anode material, the material surface shows a 0.4... Si-Si / S C-Si-O <0.7, material inside: 3 Si-C / S C-Si-O <4; where the material surface refers to the XPS spectrum measured without argon ion beam etching, and the material interior refers to the XPS spectrum measured after argon ion beam etching to a depth of 70 nm; S Si-Si The area of ​​the Si 2p fractionation peak near 98±0.5 eV is represented by S. C-Si-O The area of ​​the Si 2p fractionation near 102±0.5 eV, S Si-C The area of ​​the Si 2p peak near 101.5±0.5 eV.​​ 2. The silicon-carbon composite anode material according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​2000-4000 m². 2 / g, pore volume 0.9-1.2cm³ 3 / g.

3. The silicon-carbon composite anode material according to claim 2, characterized in that, The porous carbon is prepared by carbon source pyrolysis and then activation; the activation is a two-stage activation, the first activation is water vapor activation, and the second activation is carbon dioxide or metal hydroxide activation.

4. The silicon-carbon composite anode material according to claim 3, characterized in that, The primary activation involves using steam at 800-950℃, resulting in a pore volume of 0.5-0.7 cm³. 3 / g; In the secondary activation, carbon dioxide is used as the activating agent, and the activation temperature is 900-1000℃; during metal hydroxide activation, the activation temperature is 700-900℃; after secondary activation, the pore volume of the obtained porous carbon is 0.9-1.2 cm³. 3 / g.

5. The silicon-carbon composite anode material according to claim 1, characterized in that, In the silicon-carbon composite anode material, the Si mass percentage is 40-65 wt%, and the carbon coating thickness is 2-10 nm.

6. The method for preparing the silicon-carbon composite anode material according to any one of claims 1-5, characterized in that, Includes the following steps: (S1) Pretreatment: Porous carbon is pretreated at 900-1000℃ by introducing carbon source gas in a vapor deposition equipment. The porous carbon is obtained by pore-forming carbon source through two activation processes: the first activation is water vapor activation, and the second activation is carbon dioxide activation or metal hydroxide activation. (S2) Primary silicon deposition: Cool down to 450-500℃, introduce a mixture of silane and inert gas, and control the amount of gas introduced so that the amount of silicon deposited accounts for 10-15 wt% of the product. (S3) Secondary silicon deposition: Heat to 550-650℃, continue to introduce a mixture of silane and inert gas, and continue silicon deposition. Control the gas flow rate so that the amount of silicon deposited accounts for 40-65 wt% of the product. (S4) Carbon coating: Cool down to 500-600℃ and introduce carbon-containing process gas for carbon coating.

7. The preparation method according to claim 6, characterized in that, In step (S1), the carbon source gas is a C1-3 alkane, and the pretreatment time is 1-2 hours; and / or In steps (S2) and (S3), the silane is selected from at least one of silane, silane, dichlorosilane, and chlorosilane; the inert gas is selected from at least one of nitrogen, argon, and helium.

8. The preparation method according to claim 6, characterized in that, The porous carbon is obtained by activating the carbon source twice to create pores, followed by high-temperature recarbonization, including the following steps: (T1) The carbon source was activated once in the presence of water vapor, resulting in a pore volume of 0.5-0.7 cm³. 3 / g of the first porous carbon; (T2) The first porous carbon undergoes secondary activation using carbon dioxide or metal hydroxide as the activator, resulting in a pore volume of 0.9-1.2 cm³. 3 / g of the second porous carbon; (T3) The second porous carbon is crushed and recarbonized in a high-temperature furnace to finally obtain porous carbon.

9. The preparation method according to claim 8, characterized in that, In step (T1), the carbon source is formed by carbonizing one or more of coconut shell carbon, asphalt, petroleum coke, and resin through pyrolysis at a temperature of 700-1000℃; the steam activation temperature is 800-950℃; and / or In step (T2), when the activator is carbon dioxide, the activation temperature is 900-1000℃; when the activator is a metal hydroxide, the activation temperature is 700-900℃; and / or In step (T3), the material is crushed to a Dv50 of 5-10 μm and then recarbonized at 1100-1600℃ under an inert atmosphere for 2 hours.

10. A lithium-ion battery, characterized in that, The negative electrode includes the silicon-carbon composite negative electrode material as described in any one of claims 1-5.

Images