Silicon-carbon negative electrode material and preparation method thereof, negative electrode plate and lithium ion battery

Abstract

The invention provides a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode plate and a lithium ion battery. According to the silicon-carbon negative electrode material, silicon is deposited in the porous carbon substrate through vapor deposition; the silicon-carbon negative electrode material satisfies the following conditions: the D50 particle size E of the silicon-carbon negative electrode material satisfies 7.0 [mu] m < = E < = 8.5 [mu] m; the silicon content H in the silicon-carbon negative electrode material is more than or equal to 50% and less than or equal to 57%; the tap density TD of the silicon-carbon negative electrode material is more than or equal to 0.95 g / cm < 3 > and less than or equal to 1.10 g / cm < 3 >; the specific surface area of the silicon-carbon negative electrode material is S which is not less than 1.0 m < 2 > / g and not more than 1.5 m < 2 > / g; the following relational expressions are satisfied: relational expression I: 9 < = (S * E) < = 12.75; the relational expression II is as follows: 50 < = (H * TD) < = 60; and the relational expression III is that (100 * TD / E) is more than or equal to 11.20 and less than or equal to 15.71. According to the silicon-carbon negative electrode material, a material with high capacity, excellent low-temperature cycle performance and low expansion characteristic can be prepared without setting a complex process or additionally adding a nano additive and a surface coating modifier, so that the silicon-carbon negative electrode material has high capacity retention rate and low expansion rate in low-temperature cycle.

Description

Technical Field

[0001] This disclosure relates to the field of silicon-carbon anode material technology, and in particular to a silicon-carbon anode material and its preparation method, anode sheet, and lithium-ion battery. Background Technology

[0002] Silicon-carbon anode materials are considered key to next-generation high-energy-density lithium-ion batteries due to their high specific capacity. However, silicon materials undergo a 300% volume expansion during lithium intercalation, leading to electrode structure damage, conductive network failure, and battery swelling, resulting in a rapid deterioration in cycle performance. This is especially true at low temperatures (such as below 0°C), where the volume change-induced electrode structure damage is more severe. This is mainly because low temperatures not only reduce the lithium-ion diffusion rate but also cause changes in the microstructure of silicon at low temperatures, resulting in the loss of its stress buffering capacity. Consequently, the expansion stress that could have been buffered by plastic deformation cannot be released, leading to stress concentration and ultimately causing electrode structure fracture.

[0003] Currently, to address the issues of large volume expansion and short low-temperature cycle life in silicon-carbon anode materials, the industry mainly adopts the following technical approaches: 1) Constructing a porous carbon framework: Using porous carbon materials (such as activated carbon and template carbon) as a carrier, silicon is loaded into its pores, and the pore space is used to buffer volume expansion. However, this method is often complex, and excessively high porosity will sacrifice the tap density and volumetric energy density of the material, resulting in low tap density and volumetric energy density of the final lithium-ion battery.

[0004] 2) Adding nanofunctional agents: Adding nano-additives such as aluminosilicates and carbon nanotubes to the electrode slurry can enhance the mechanical strength and ionic / electronic conductivity of the electrode. However, the introduction of additives usually increases costs and reduces the proportion of active material, affecting the energy density of lithium-ion batteries.

[0005] 3) Surface coating modification: Silicon-carbon particles are coated with polymers (such as triblock copolymers) or inorganic materials (such as oxides) to form a core-shell structure to stabilize the interface. However, this method has extremely high requirements for the uniformity, density and bonding force of the coating layer with the core, making process control difficult. In addition, the introduction of the coating layer will hinder lithium-ion migration and affect the cycle life of lithium-ion batteries.

[0006] 4) Optimize the deposition process: Improve the temperature and gas flow fields of the vapor deposition reactor (such as a fluidized bed) to obtain more uniform silicon-carbon composite particles. However, this method mainly addresses the consistency issue of CVD silicon-carbon anode materials during preparation, but does not solve the problems of material volume expansion and low-temperature cycle life.

[0007] Therefore, there is an urgent need for a silicon-carbon anode material that can simultaneously achieve high capacity, excellent low-temperature cycling performance, and low expansion characteristics. Summary of the Invention

[0008] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a silicon-carbon anode material with high capacity, excellent low-temperature cycling performance, and low expansion characteristics that is better coordinated by controlling the "particle size E", "silicon content H", "taper density TD" and "specific surface area S" of the silicon-carbon anode material generated by vapor deposition. This ensures that a silicon-carbon anode material with high capacity, excellent low-temperature cycling performance, and low expansion characteristics can be prepared without setting specific complex processes or adding additional nano-additives or surface coating modifiers. This allows the material to simultaneously maintain high capacity retention and low expansion rate during low-temperature cycling, achieving a silicon-carbon anode material with low expansion rate and excellent low-temperature cycle life for lithium-ion batteries, as well as its preparation method, anode sheet, and lithium-ion battery.

[0009] The purpose of this disclosure is achieved through the following technical solution: A silicon-carbon anode material, wherein silicon is deposited in a porous carbon substrate via vapor deposition; the silicon-carbon anode material satisfies the following conditions: The D50 particle size of the silicon-carbon anode material is E, which satisfies 7.0μm≤E≤8.5μm; The silicon content in the silicon-carbon anode material is H, satisfying 50% ≤ H ≤ 57%; The tap density of the silicon-carbon anode material is TD, which satisfies 0.95 g / cm³. 3 ≤TD≤1.10g / cm 3 ; The specific surface area S of the silicon-carbon anode material satisfies 1.0 m². 2 / g≤S≤1.5m 2 / g; Furthermore, E, H, TD, and S simultaneously satisfy the following relationship: Relationship I: 9 ≤ (S × E) ≤ 12.75; Relationship II: 50 ≤ (H × TD) ≤ 60; Relation III: 11.20≤(100×TD / E)≤15.71.

[0010] In one embodiment, the relation I satisfies: 10 ≤ (S × E) ≤ 12.5; and / or, The relation II satisfies: 52 ≤ (H × TD) ≤ 58; and / or, The relation III satisfies: 12≤(100×TD / E)≤15.

[0011] In one embodiment, the resistivity of the silicon-carbon anode material is R, which satisfies 0.4Ω·cm≤R≤0.9Ω·cm.

[0012] In one embodiment, the silicon source gas flow rate during vapor deposition is 15 L / min-80 L / min, and the silicon deposition time is 4 h-8 h; and / or, The deposition temperature for silicon is 500℃-700℃; and / or, The deposition pressure for silicon is 5 kPa-6 kPa.

[0013] In one embodiment, the gas velocity of the mixed gas during vapor deposition is 0.2 m / s to 0.3 m / s; and / or, During vapor deposition, the silicon source accounts for 10%-30% of the volume concentration of the mixed gas.

[0014] In one embodiment, the D50 particle size of the porous carbon substrate is 7.5 μm-9.5 μm; and / or, The porous carbon substrate has a specific surface area of ​​1500 m². 2 / g-2000m 2 / g.

[0015] In one embodiment, the porous carbon substrate includes at least one of petroleum coke-based activated carbon, resin carbon, and biomass carbon.

[0016] A method for preparing a silicon-carbon anode material includes the following steps: The carbon precursor was pretreated to obtain a porous carbon substrate; The porous carbon substrate was placed in a vapor deposition reactor, and a silicon source was introduced to react with an inert gas to obtain a primary composite material. Carbon is coated onto the vapor deposition reactor using a carbon source gas to obtain the silicon-carbon anode material described in any of the above embodiments.

[0017] A negative electrode sheet comprising the silicon-carbon negative electrode material described in any of the above embodiments.

[0018] A lithium-ion battery comprising the negative electrode sheet described in any of the above embodiments.

[0019] In one embodiment, the low-temperature (0°C) thickness expansion rate of the lithium-ion battery is <10%; and / or, The lithium-ion battery retains >92% of its capacity over 200 cycles at 0°C.

[0020] Compared with the prior art, this disclosure has at least the following advantages: By controlling the "particle size E", "silicon content H", "tap density TD" and "specific surface area S" of the silicon-carbon anode material generated by vapor deposition, the relationship between silicon content, tap density, high capacity and expansion buffer capacity in the silicon-carbon anode material is well coordinated. This ensures that high-capacity silicon-carbon anode materials with excellent low-temperature cycling performance and low expansion characteristics can be prepared without setting specific complex processes or adding additional nano-additives or surface coating modifiers. This allows the anode material to simultaneously maintain high capacity retention and low expansion rate during low-temperature cycling, thus achieving low expansion rate and excellent low-temperature cycle life of lithium-ion batteries.

[0021] Since the D50 particle size E of the silicon-carbon anode material satisfies 7.0 μm ≤ E ≤ 8.5 μm, which is a relatively small particle size, it is beneficial to form a smaller ion diffusion path. However, the small particle size leads to an increase in the specific surface area of ​​the silicon-carbon anode material. An excessively large specific surface area increases side reactions in lithium-ion batteries, causing SEI film instability and increased interfacial impedance, thus affecting its low-temperature cycling performance. Therefore, in this disclosure, by reasonably controlling the relationship I between the specific surface area S and the particle size E to satisfy 9 ≤ (S × E) ≤ 12.75, the contradiction between small particle size and low specific surface area is better coordinated, ensuring that the specific surface area S of the silicon-carbon anode material is at a relatively low level (1.0 μm). 2 / g≤S≤1.5m 2 The method achieves a good balance between specific surface area (S) and particle size (E), breaking the physical correlation that decreasing particle size increases specific surface area according to geometric principles. It achieves an optimal balance between a smaller ion diffusion path (determined by particle size E) and a stable interfacial reaction environment (determined by the size of S), ensuring that the prepared silicon-carbon anode material has both small particle size and low surface area, thereby significantly improving interfacial stability and low-temperature cycle life at low temperatures. It effectively avoids the problem of poor electrolyte wetting due to excessively small S, which would affect ion diffusion, while avoiding the problem of excessively large S, which would increase side reactions with the electrolyte and affect low-temperature cycle performance.

[0022] Because the silicon content H in silicon-carbon anode materials must satisfy 50% ≤ H ≤ 57% to ensure the fabrication of high-capacity lithium-ion batteries; however, a high silicon content (>50%) leads to a porous structure in the silicon-carbon anode material, resulting in a low tap density TD. Therefore, in this disclosure, by reasonably controlling the relationship between silicon content H and tap density TD (Equation II) to satisfy 50 ≤ (H × TD) ≤ 60, the contradiction between the silicon content H and tap density TD in the silicon-carbon anode material is cleverly balanced, ensuring that the tap density TD is at a relatively high level (0.95 g / cm³). 3 ≤TD≤1.10g / cm 3 This ensures that silicon-carbon anode materials possess both high capacity and high tap density, which is beneficial for preparing high-capacity lithium-ion batteries.

[0023] Furthermore, due to the tap density being 0.95 g / cm³ 3 ≤TD≤1.10g / cm 3 The silicon-carbon anode material within the range has a certain buffer volume change, that is, an effective buffer volume, which can better suppress the structural failure of silicon-carbon anode material caused by uneven silicon expansion at low temperature, and effectively avoid the problem that silicon-carbon anode materials with high tap density cannot suppress silicon expansion due to small effective buffer volume.

[0024] By controlling the ratio of tap density to particle size, the internal structural compactness of the material is adjusted to satisfy Equation III: 11.20≤(100×TD / E)≤15.71. This ensures that the silicon-carbon anode material has optimal expansion buffer space. Especially when Equation II between silicon content H and tap density TD satisfies 50≤(H×TD)≤60, the silicon-carbon anode material can effectively buffer the volume change stress of silicon expansion under the synergistic effect of expansion buffer space and effective buffer volume, suppressing the low-temperature expansion rate of lithium-ion batteries. At the same time, it better ensures that the silicon-carbon anode material is not prone to cracking, effectively suppressing the generation and propagation of surface cracks in the silicon-carbon anode material, reducing the continuous exposure of fresh interfaces in the silicon-carbon anode material, thereby stabilizing the interface film and optimizing the low-temperature performance of lithium-ion batteries. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a scanning electron microscope image of a silicon-carbon anode material according to an embodiment of the present invention. Detailed Implementation

[0027] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0028] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments: An embodiment of a silicon-carbon anode material, wherein the silicon-carbon anode material is formed by vapor deposition of silicon within a porous carbon substrate; the silicon-carbon anode material satisfies the following conditions: the D50 particle size of the silicon-carbon anode material is E, satisfying 7.0 μm ≤ E ≤ 8.5 μm; the silicon content in the silicon-carbon anode material is H, satisfying 50% ≤ H ≤ 57%; the tap density of the silicon-carbon anode material is TD, satisfying 0.95 g / cm³. 3 ≤TD≤1.10g / cm 3 The specific surface area of ​​the silicon-carbon anode material is S, which satisfies 1.0 m² / s. 2 / g≤S≤1.5m 2 / g; and E, H, TD and S simultaneously satisfy the following relationships: Relationship I: 9≤(S×E)≤12.75; Relationship II: 50≤(H×TD)≤60; Relationship III: 11.20≤(100×TD / E)≤15.71.

[0031] It is understandable that by controlling the "particle size E", "silicon content H", "taper density TD" and "specific surface area S" of the silicon-carbon anode material generated by vapor deposition, the relationship between silicon content, tap density, high capacity and expansion buffer capacity in the silicon-carbon anode material is well coordinated. This ensures that high-capacity silicon-carbon anode materials with excellent low-temperature cycling performance and low expansion characteristics can be prepared without setting specific complex processes or adding additional nano-additives or surface coating modifiers. This allows the anode material to simultaneously maintain high capacity retention and low expansion rate during low-temperature cycling, thus achieving low expansion rate and excellent low-temperature cycle life of lithium-ion batteries.

[0032] It is also understandable that, since the D50 particle size E of the silicon-carbon anode material satisfies 7.0 μm ≤ E ≤ 8.5 μm, which is a relatively small particle size, it is conducive to forming a smaller ion diffusion path. However, the small particle size leads to an increase in the specific surface area of ​​the silicon-carbon anode material. An excessively large specific surface area increases the side reactions in the lithium-ion battery, leading to SEI film instability and increased interfacial impedance, thus affecting its low-temperature cycling performance. Therefore, in this disclosure, by reasonably controlling the relationship I between the specific surface area S and the particle size E to satisfy 9 ≤ (S × E) ≤ 12.75, the contradiction between small particle size and low specific surface area is better coordinated, ensuring that the specific surface area S of the silicon-carbon anode material is at a relatively low level (1.0 μm). 2 / g≤S≤1.5m 2 The method achieves a good balance between specific surface area (S) and particle size (E), breaking the physical correlation that decreasing particle size increases specific surface area according to geometric principles. It achieves an optimal balance between a smaller ion diffusion path (determined by particle size E) and a stable interfacial reaction environment (determined by the size of S), ensuring that the prepared silicon-carbon anode material has both small particle size and low surface area, thereby significantly improving interfacial stability and low-temperature cycle life at low temperatures. It effectively avoids the problem of poor electrolyte wetting due to excessively small S, which would affect ion diffusion, while avoiding the problem of excessively large S, which would increase side reactions with the electrolyte and affect low-temperature cycle performance.

[0033] It is also understandable that the silicon content H in the silicon-carbon anode material must satisfy 50% ≤ H ≤ 57% to ensure the fabrication of a high-capacity lithium-ion battery; however, a high silicon content (>50%) leads to a loose structure in the silicon-carbon anode material, resulting in a low tap density TD. Therefore, in this disclosure, by reasonably controlling the relationship between silicon content H and tap density TD (Equation II) to satisfy 50 ≤ (H × TD) ≤ 60, the contradiction between the silicon content H and tap density TD of the silicon-carbon anode material is cleverly balanced, ensuring that the tap density TD is at a relatively high level (0.95 g / cm³). 3 ≤TD≤1.10g / cm 3 This ensures that silicon-carbon anode materials possess both high capacity and high tap density, which is beneficial for preparing high-capacity lithium-ion batteries.

[0034] This is understandable. Furthermore, the tap density is 0.95 g / cm³. 3 ≤TD≤1.10g / cm 3 The silicon-carbon anode material within the range has a certain buffer volume change, that is, an effective buffer volume, which can better suppress the structural failure of silicon-carbon anode material caused by uneven silicon expansion at low temperature, and effectively avoid the problem that silicon-carbon anode materials with high tap density cannot suppress silicon expansion due to small effective buffer volume.

[0035] It can also be understood that by further controlling the structural density per unit particle size of the silicon-carbon anode material to satisfy Equation III: 11.20≤(100×TD / E)≤15.71, the silicon-carbon anode material can be ensured to have the optimal expansion buffer space. In particular, when used in conjunction with Equation II, the silicon-carbon anode material can better buffer the volume change stress of silicon expansion under the synergistic effect of the expansion buffer space and the effective buffer volume, thus suppressing the low-temperature expansion rate of the lithium-ion battery. At the same time, it can better ensure that the silicon-carbon anode material is not prone to cracking, effectively suppressing the generation and propagation of surface cracks in the silicon-carbon anode material, reducing the continuous exposure of the fresh interface of the silicon-carbon anode material, thereby stabilizing the interface film and optimizing the low-temperature performance of the lithium-ion battery.

[0036] In one embodiment, the relation I satisfies: 10≤(S×E)≤12.5; especially in conjunction with the use of the relation II satisfying: 52≤(H×TD)≤58 and the relation III satisfying: 12≤(100×TD / E)≤15, to ensure the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance and low expansion characteristics.

[0037] In one embodiment, the resistivity of the silicon-carbon anode material is R, which satisfies 0.4Ω·cm≤R≤0.9Ω·cm, to ensure that the silicon-carbon anode material has good conductivity.

[0038] It is understandable that if the silicon source gas flow rate, silicon source deposition rate, silicon source deposition reaction temperature, or silicon deposition pressure is too low during vapor deposition, the silicon source molecule diffusion rate will be insufficient, resulting in a small amount of silicon deposition and making it impossible to prepare silicon-carbon anode materials with high silicon content. If the silicon source gas flow rate, silicon source deposition rate, silicon source deposition reaction temperature, or silicon deposition pressure is too high during vapor deposition, the silicon source molecule diffusion gas flow turbulence will be intensified, resulting in a large amount of silicon deposition. This will easily lead to homogeneous nucleation of silicon particles in the gas phase to form free silicon. Therefore, in one embodiment, by controlling the silicon source gas flow rate during vapor deposition to 15 L / min-80 L / min, the silicon deposition time to 4 h-8 h, the silicon deposition reaction temperature to 500 °C-700 °C, and the silicon deposition pressure to 5 kPa-6 kPa, it is ensured that silicon can be uniformly deposited within the pores of the porous carbon substrate. This facilitates the preparation of silicon particles with suitable particle sizes, ensuring that the deposited silicon can be well deposited within the pores. On the one hand, this ensures a high bonding force between silicon and the porous carbon substrate, thereby reducing the probability of silicon detachment during expansion. On the other hand, it also ensures that the stacking density of the deposited silicon particles is relatively uniform and has small gaps, thus ensuring that the silicon particles themselves have a certain effective buffer volume. This is beneficial for preparing a silicon content (50% ≤ H ≤ 57%) and a suitable tap density (0.95 g / cm³). 3 ≤TD≤1.10g / cm 3), and a relatively low specific surface area (1.0 m²). 2 / g≤S≤1.5m 2 / g), so that the final silicon-carbon anode material can simultaneously satisfy relation I, relation II and relation III, that is, to prepare a silicon-carbon anode material with high capacity, excellent low temperature cycling performance and low expansion characteristics, so that it can simultaneously have high capacity retention and low expansion rate in low temperature cycling, thus realizing low expansion rate and excellent low temperature cycle life of lithium-ion batteries.

[0039] In one embodiment, the gas velocity of the mixed gas during vapor deposition is 0.2 m / s to 0.3 m / s to ensure that silicon can be uniformly deposited within the porous carbon substrate.

[0040] It is understandable that if the volume concentration of the silicon source is below 10%, the deposition rate of silicon on the carbon surface will be too low, making it impossible to prepare high-capacity silicon-carbon anode materials. If the volume concentration of the silicon source is above 30%, it will easily lead to homogeneous nucleation of silicon particles in the gas phase, forming free silicon, thereby destroying the composite structure of the silicon-carbon anode material. Therefore, in one embodiment, the volume concentration of the silicon source in the mixed gas is 10%-30% during vapor deposition to ensure that the concentration of the silicon source in the mixed gas is suitable, thereby ensuring the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance, and low expansion characteristics.

[0041] In one embodiment, the D50 particle size of the porous carbon substrate is 7.5 μm-9.5 μm; particularly, the specific surface area of ​​the porous carbon substrate is 1500 m². 2 / g-2000m 2 The use of / g ensures that the porosity of the porous carbon substrate is 70%-90%, thereby ensuring that the porous carbon substrate has a good loading volume. At the same time, the silicon source accounts for 10%-30% of the volume concentration of the mixed gas, the gas velocity of the mixed gas is 0.2m / s-0.3m / s, and the silicon source gas flow rate is 15L / min-80L / min. This allows the silicon source to be decomposed into silicon at 500℃-700℃ and uniformly deposited in the pores of the porous carbon substrate. This is beneficial for preparing silicon-carbon anode materials that simultaneously satisfy the buffering capacity of relation II and relation III, thus ensuring the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance, and low expansion characteristics.

[0042] In one embodiment, the porous carbon substrate includes at least one of petroleum coke-based activated carbon, resin carbon, and biomass carbon.

[0043] In one embodiment, the porous carbon substrate is resin carbon.

[0044] In one embodiment, the resin carbon includes at least one of phenolic resin carbon, polyimide resin carbon, and epoxy resin carbon.

[0045] In one embodiment, the resin carbon is phenolic resin carbon. Because phenolic resin carbon has the advantages of strong controllability of pore structure, excellent conductivity and low process cost, it can provide a stable and high-capacity carrier for silicon deposition, ensuring the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance and low expansion characteristics.

[0046] In one embodiment, the resin carbon includes at least two different pore sizes, allowing silicon to preferentially deposit in the micropores, mainly because the specific surface area of ​​the micropores is larger than that of the mesopores, making it easier for the pyrolyzed silicon to deposit on the surface of the micropores; and then deposited in the mesopores, thereby facilitating the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance and low expansion characteristics.

[0047] In one embodiment, the porous carbon substrate comprises micropores and mesopores. The mesopores have a pore size of 2 nm-50 nm, and the micropores have a pore size of <2 nm. This is particularly advantageous when the silicon source accounts for 10%-30% of the volume concentration of the mixed gas, the gas velocity of the mixed gas is 0.2 m / s-0.3 m / s, the silicon source flow rate is 15 L / min-80 L / min, the silicon deposition time is 4 h-8 h, and the silicon deposition reaction temperature is 500 °C-700 °C. This ensures that silicon is uniformly deposited within the micropores, while the mesopores have only a small amount or no silicon deposited. This facilitates the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance, and low expansion characteristics.

[0048] In one embodiment, the porous carbon substrate includes a substrate body and multiple sets of micro-mesopore rings. The sets of micro-mesopore rings are arranged sequentially and at intervals along the substrate body to achieve the spacing between micropores and mesopores, so that the added mesopores can provide better buffering for silicon expansion.

[0049] It should be noted that, in low-temperature environments (0℃-10℃), the brittle transition of silicon is more pronounced than that of porous carbon substrates. If a large number of silicon particles are located around the outer periphery of the substrate, these particles are more susceptible to brittle transition due to external temperature changes, resulting in a loss of stress buffering capacity. Therefore, in this disclosure, the density of micropores in each group of micro-mesopore rings decreases sequentially from the inside to the outside of the substrate, while the density of each mesopore increases sequentially from the inside to the outside of the substrate. This effectively reduces the number of silicon particles around the outer periphery of the substrate, resulting in a larger distribution area of ​​mesopores around the outer periphery, which better absorbs and buffers temperature changes, thereby reducing the impact on the internal silicon particles.

[0050] Understandably, to facilitate the operator's quick selection of a suitable porous carbon substrate, the operator can refer to the following relationship IV-1: This ensures that the operator can quickly select the corresponding pore volume of the porous carbon substrate, according to equation IV-2: This allows us to obtain a reference for the specific surface area of ​​porous carbon substrates, enabling the preparation of silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance, and low expansion characteristics.

[0051] Where H refers to silicon content (%), ρ Si The true density of silicon (approximately 2.33 g / cm³) 3 ), TD refers to the tap density of the final material, E is the D50 of porous carbon, V pore Pore ​​volume (cm) of porous carbon substrate 3 / g), and its total pore volume (usually contributed by micropores and mesopores) was determined by gas adsorption method. BET This refers to the specific surface area of ​​a porous carbon substrate.

[0052] In one embodiment, the micropore density is 0.5 × 10⁻⁶. 9 -5.0×10 9 pcs / square centimeter

[0053] In one embodiment, the mesopore density is 1.0 × 10⁻⁶. 7 -1.0×10 8 pcs / square centimeter

[0054] This disclosure also provides a method for preparing a silicon-carbon anode material, comprising the following steps: first, pretreating a carbon precursor to obtain a porous carbon substrate; then, placing the porous carbon substrate in a vapor deposition reactor and introducing a silicon source and an inert gas to perform a silicon deposition reaction to obtain a primary composite material; finally, coating the vapor deposition reactor with carbon source gas to obtain the silicon-carbon anode material described in any of the above embodiments.

[0055] In one embodiment, the pretreatment step of the porous carbon substrate includes the following specific steps: preheating the porous carbon substrate at high temperature (800℃-1200℃, time 1h-4h) under an inert atmosphere to remove functional groups on the surface of the porous carbon substrate, which facilitates the formation of stable Si-C bonds between silicon and the porous carbon substrate. This improves the uniformity and stability of the interface between silicon and the porous carbon substrate, better suppressing silicon expansion at low temperatures and reducing the occurrence of cracks or silicon shedding in the silicon-carbon anode material. It also effectively avoids silicon preferentially depositing and agglomerating in high-functionality areas, which would lead to an uneven interface of bonding strength between silicon and the porous carbon substrate.

[0056] In one embodiment, in the step of placing the porous carbon substrate in a vapor deposition reactor and introducing a silicon source and an inert gas to perform a silicon deposition reaction to obtain a primary composite material, the volume concentration of the silicon source in the mixed gas is controlled to be 10%-30%, the deposition reaction temperature is controlled to be 500℃-700℃, the gas velocity of the mixed gas is 0.2m / s-0.3m / s, and the gas flow rate of the silicon source is 15L / min-80L / min. This ensures that silicon can be uniformly and stably deposited in the pores of the porous carbon, thereby preparing a silicon-carbon anode material with high capacity, excellent low-temperature cycling performance, and low expansion characteristics.

[0057] In one embodiment, the deposition reaction temperature is 500°C-650°C to ensure that silicon can be deposited more uniformly in the pores of the porous carbon substrate under low temperature conditions, thereby ensuring the preparation of silicon-carbon anode materials with high tap density and reducing the energy consumption of the deposition reaction.

[0058] In one embodiment, the deposition reaction temperature is controlled in stages to avoid localized overheating that could lead to increased interfacial impedance due to silicon agglomerates. Furthermore, the temperature difference between the top and bottom of the fluidized bed is ≤20°C.

[0059] It should be noted that although silicon-carbon coating (CVD carbon layer) is a common method for preparing silicon-carbon anode materials, the silicon-based anodes prepared so far generally exhibit a 3-10 fold increase in charge transfer resistance (Rct) after cycling. This is especially true at low temperatures (0℃-10℃) due to the combined effects of ion diffusion freezing and interfacial stress concentration, which can cause the Rct to increase by 10-20 times after cycling, thereby deteriorating the low-temperature cycling performance of lithium-ion batteries.

[0060] Therefore, in one embodiment, during the carbon coating operation of the primary composite material using a carbon source gas, the carbon source gas flow rate is controlled at 0.1 L / min-0.2 L / min, the carbon coating temperature at 500℃-600℃, and the time at 1h-2h. This ensures the formation of a 2nm-5nm thick carbon coating layer on the surface of the primary composite material. Compared to traditional thicker carbon coating layers, the 2nm-5nm carbon coating layer of this disclosure effectively reduces the electron transport path length, thereby effectively alleviating the problem of electron conduction obstruction at low temperatures. Furthermore, the thin carbon layer facilitates tighter interfacial contact with silicon, enabling rapid charge transport and helping to prepare silicon-based anode materials with resistivity (R) within the range of 0.4Ω·cm ≤ R ≤ 0.9Ω·cm. This further reduces the problem of ion diffusion freezing at low temperatures, ensuring that Rct only increases by about 2 times after cycling. In addition, the thin carbon layer is beneficial for the development of thinner lithium-ion batteries.

[0061] It is also understandable that by controlling the carbon source gas flow rate to 0.1L / min-0.2L / min, on the one hand, it is beneficial to form a porosity of 40%-60%, thereby ensuring good flexibility of the coated carbon layer and effectively suppressing the expansion of silicon at low temperature. On the other hand, it is beneficial to form pore sizes of 2nm-50nm, which are not larger than the particle size of silicon particles, thereby ensuring that the added coated carbon layer can achieve the function of limiting silicon particles, further improving the bonding strength between silicon particles and porous carbon substrate, and effectively avoiding the problem of silicon particles falling off due to large external forces when not in use, such as large vibrations during transportation.

[0062] In one embodiment, the carbon source includes at least one of ethylene and propylene.

[0063] In one embodiment, the silicon source includes at least one of silane, dichlorosilane (SiH2Cl2), and silicon tetrachloride (SiCl4).

[0064] In one embodiment, the inert gas is a high-purity inert gas, such as argon.

[0065] In one embodiment, the purity of the high-purity inert gas is 99.99%-99.999%.

[0066] In one embodiment, after placing the porous carbon substrate in a vapor deposition reactor and introducing a silicon source and inert gas for silicon deposition, and before introducing a carbon source gas into the vapor deposition reactor for carbon coating, the following step is further included: heat treatment of the primary composite material (temperature 800℃-850℃, time 1h-4h) to further strengthen the bonding between silicon and the porous carbon substrate, eliminate internal stress, and facilitate the preparation of silicon-carbon anode materials with fewer cracks, strong bonding, high capacity, excellent low-temperature cycling performance, and low expansion characteristics. For details, please refer to [link to relevant documentation]. Figure 1 .

[0067] This disclosure also provides a negative electrode sheet, comprising the silicon-carbon negative electrode material of any of the above embodiments.

[0068] In one embodiment, the negative electrode comprises graphite and 20% silicon-carbon negative electrode material.

[0069] This disclosure also provides a lithium-ion battery, including the negative electrode sheet described in any of the above embodiments, to obtain a battery that simultaneously possesses high capacity, excellent low-temperature cycling performance, and good stability of expansion and post-cycle Rct with minimal increase. Specifically, in one embodiment, the low-temperature (0°C) thickness expansion rate of the lithium-ion battery is <10%; the capacity retention rate of the lithium-ion battery at 0°C for 200 cycles is >92%.

[0070] In one embodiment, the lithium-ion battery includes a positive electrode. The positive electrode is lithium cobalt oxide (LCO).

[0071] The following are some specific examples. When %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively list all possible scenarios, and unless otherwise specified, the materials used in the examples are commercially available.

[0072] Example 1 S1, V is obtained through the relational formula. pore ≥0.8cm 3 / g, S BET ≥1420 m 2 / g, select a suitable phenolic resin carbon (D50 particle size 7.6μm, specific surface area 1700m²). 2 / g, total pore volume 0.8cm³ 3 / g, the pore size of the micropores is ≤2nm, the pore size of the mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate. Then, the substrate is subjected to high-temperature preheating treatment (1000℃, 2h) under argon atmosphere to obtain a porous carbon substrate. S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 20% of the mixed gas concentration, silane gas flow rate is 50L / min, and mixed gas velocity is 0.25m / s) are introduced to carry out silicon deposition reaction (deposition reaction temperature is 600℃, silicon deposition time is 8h, and deposition pressure is 5kPa) to obtain the primary composite material. S3. Heat treatment of the primary composite material (temperature 800℃, time 2h); S4. Carbon coating is performed on the vapor deposition reactor by passing ethylene gas (gas flow rate of 0.15 L / min) (temperature 580 °C, time 1 h) to form a 3 nm thick coated carbon layer (porosity of 50% and pore size of 20 nm) on the surface of the primary composite material; thus obtaining silicon-carbon anode material.

[0073] Example 2 S1, V is obtained through the relational formula. pore ≥0.795cm 3 / g, S BET ≥1420 m 2 / g, select resin carbon (D50=7.5μm, specific surface area 1650m²) 2 / g, total pore volume 0.85cm³ 3 / g, the pore size of micropores is ≤2nm, the pore size of mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate), and preheated at 1050℃ for 2h under argon.

[0074] S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 18% of the mixed gas concentration, the silane gas flow rate is 45 L / min, and the mixed gas velocity is 0.22 m / s) are introduced to carry out a silicon deposition reaction (deposition reaction temperature is 580℃, silicon deposition time is 7.5 h, and deposition pressure is 5 kPa) to obtain the primary composite material. S3. Heat treatment of the primary composite material (temperature 820℃, time 2h); S4. Carbon coating is performed on the vapor deposition reactor by passing ethylene gas (gas flow rate of 0.14 L / min) (temperature 550 °C, time 2 h) to form a 3 nm thick coated carbon layer (porosity of 48% and pore size of 18 nm) on the surface of the primary composite material; thus obtaining silicon-carbon anode material.

[0075] Example 3 S1, calculated using relation IV, yields Vpore ≥ 0.813m. 3 / g, SBET≥1455 m 2 / g, selected petroleum coke-based activated carbon (D50=7.8μm, specific surface area 1800m²). 2 / g, total pore volume 0.85cm³ 3 / g, the pore size of the micropores is ≤2nm, the pore size of the mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate), and preheated at 1000℃ for 3h under argon.

[0076] S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 22% of the mixed gas concentration, silane gas flow rate is 5.5 L / min, gas velocity is 0.26 m / s) are introduced to carry out silicon deposition reaction (deposition reaction temperature is 620℃, silicon deposition time is 9 h, deposition pressure is 6 kPa) to obtain primary composite material. S3. Heat treatment of the primary composite material (temperature 800℃, 2.5h).

[0077] S4. Carbon coating is performed by passing ethylene gas (gas flow rate of 0.16 L / min) through the vapor deposition reactor (temperature 570°C, time 1 h) to form a carbon coating layer with a thickness of 4 nm (porosity of 52% and pore size of 22 nm) on the surface of the primary composite material, thereby obtaining silicon-carbon anode material.

[0078] Example 4 S1, V is obtained through the relational formula. pore ≥0.855cm 3 / g, S BET ≥1515 m 2 / g, selected phenolic resin carbon (D50=8.0μm, specific surface area 1750m²). 2 / g, total pore volume 0.88cm³ 3 / g, the pore size of the micropores is ≤2nm, the pore size of the mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate. Then, the substrate is subjected to high-temperature preheating treatment (1100℃, 2h) under argon atmosphere to obtain a porous carbon substrate. S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 22% of the mixed gas concentration, silane gas flow rate is 65L / min, and mixed gas velocity is 0.28m / s) are introduced to carry out a silicon deposition reaction (deposition reaction temperature is 650℃, silicon deposition time is 9h, and deposition pressure is 5.5kPa) to obtain the primary composite material. S3. Heat treatment of primary composite material (temperature 830℃, time 2h).

[0079] S4. Carbon coating is performed on the vapor deposition reactor by passing ethylene gas (gas flow rate of 0.18 L / min) (temperature 580℃, 1h) to form a carbon coating layer with a thickness of 4 nm (porosity of 55% and pore size of 25 nm) on the surface of the primary composite material; thus obtaining silicon-carbon anode material.

[0080] Example 5 S1, V is obtained through the relational formula. pore ≥0.809cm 3 / g, S BET ≥1428 m 2 / g, select resin carbon (D50=8.0μm, specific surface area 1550m²) 2 / g, total pore volume 0.75cm³ 3 / g, the pore size of micropores is ≤2nm, the pore size of mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate), and preheated at 1000℃ for 2.5h under argon.

[0081] S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 15% of the mixed gas concentration, the silane gas flow rate is 40 L / min, and the mixed gas velocity is 0.20 m / s) are introduced to carry out a silicon deposition reaction (deposition reaction temperature is 550℃, silicon deposition time is 6.5 h, and deposition pressure is 5 kPa) to obtain the primary composite material. S3. Heat treatment of the primary composite material (temperature 810℃, time 2h); S4. Carbon coating is performed on the vapor deposition reactor by passing ethylene gas (gas flow rate of 0.18 L / min) (temperature 540 °C, time 1 h) to form a 2.5 nm thick coated carbon layer (porosity of 45% and pore size of 15 nm) on the surface of the primary composite material; thus obtaining silicon-carbon anode material.

[0082] Example 6 S1. Calculated using the relational formula, Vpore ≥ 0.842cm 3 / g, S BET ≥1525 m 2 / g, selected petroleum coke-based activated carbon (D50=8.2μm, specific surface area 1850m²) 2 / g, total pore volume 0.85cm³ 3 / g, the pore size of micropores is ≤2nm, the pore size of mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate), and preheated at 1050℃ for 3h under argon.

[0083] S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 28% of the mixed gas concentration, silane gas flow rate is 75L / min, gas velocity is 0.30m / s) are introduced to carry out silicon deposition reaction (deposition reaction temperature is 680℃, silicon deposition time is 9h, deposition pressure is 6kPa) to obtain primary composite material. S3. Heat treatment of primary composite material (temperature 840℃, 2h); S4. Carbon coating is performed by passing ethylene gas (gas flow rate of 0.19 L / min) through the vapor deposition reactor (temperature 590°C, time 1 h) to form a 5 nm thick coated carbon layer (porosity of 58% and pore size of 30 nm) on the surface of the primary composite material, thereby obtaining silicon-carbon anode material.

[0084] Example 7 S1. Calculated using the relational formula, Vpore ≥ 0.80cm 3 / g, SBET≥1455 m 2 / g, using phenolic resin carbon (D50=7.9μm, specific surface area 1680m²). 2 / g, total pore volume 0.8cm³ 3 / g, the pore size of the micropores is ≤2nm, the pore size of the mesopores is 5nm-30nm, the micropore density decreases from the inside to the outside of the substrate, and the mesopore density increases from the inside to the outside of the substrate), and then the substrate is preheated at high temperature in an argon atmosphere (1000℃, 2h).

[0085] S2. The porous carbon substrate is placed in a vapor deposition reactor, and silane and argon gas (silane accounts for 20% of the mixed gas concentration, silane gas flow rate is 50L / min, and mixed gas velocity is 0.25m / s) are introduced to carry out silicon deposition reaction (deposition reaction temperature is 600℃, silicon deposition time is 8h, and deposition pressure is 5kPa) to obtain the primary composite material. S3. Heat treatment of primary composite material (temperature 800℃, time 2h); S4. Carbon coating is performed on the vapor deposition reactor by passing ethylene gas (gas flow rate of 0.15 L / min) (temperature 550 °C, time 1 h) to form a 3 nm thick coated carbon layer (porosity of 50% and pore size of 20 nm) on the surface of the primary composite material; thus obtaining silicon-carbon anode material.

[0086] Comparative Example 1 The difference from Example 1 is that the silane concentration in step S2 is 20%, the silane flow rate is 50 L / min, the mixing gas velocity is 0.25 m / s, the deposition reaction temperature is 600°C, the silicon deposition time is 8 h, and the deposition pressure is 5 kPa. Instead, the silane concentration in step S2 is 12%, the silane flow rate is 14 L / min, the mixing gas velocity is 0.15 m / s, the deposition reaction temperature is 480°C, the silicon deposition time is 10 h, and the deposition pressure is 4 kPa. All other parameters remain the same.

[0087] Comparative Example 2 The difference from Example 1 is that the silane concentration in step S2 is 20%, the silane flow rate is 50 L / min, the mixing gas velocity is 0.25 m / s, the deposition reaction temperature is 600°C, the silicon deposition time is 8 h, and the deposition pressure is 5 kPa. Instead, the silane concentration in step S2 is 30%, the silane flow rate is 85 L / min, the mixing gas velocity is 0.33 m / s, the deposition reaction temperature is 750°C, the silicon deposition time is 3 h, and the deposition pressure is 7 kPa. All other parameters remain the same.

[0088] Comparative Example 3 The difference from Example 1 is that the specific surface area of ​​1700m² in step S1 is... 2Replace / g with 1400m 2 / g, the rest remain unchanged.

[0089] Comparative Example 4 The difference from Example 1 is that the specific surface area of ​​1700m² in step S1 is... 2 Replace / g with 2200m 2 / g, the rest remain unchanged.

[0090] Comparative Example 5 The difference from Example 1 is that the D50 particle size of 7.6 μm in step S1 is replaced with D50 = 11.0 μm, while the rest remains the same.

[0091] Comparative Example 6 The difference from Example 1 is that the D50 particle size of 7.6 μm in step S1 is replaced with D50 = 6.5 μm, while the rest remains the same.

[0092] Comparative Example 7 The difference from Example 1 is that the arrangement density of micropores decreases sequentially from the inside to the outside of the substrate, and the arrangement density of mesopores increases sequentially from the inside to the outside of the substrate. Instead, the arrangement density of micropores increases sequentially from the inside to the outside of the substrate, and the arrangement density of mesopores decreases sequentially from the inside to the outside of the substrate. The rest remains unchanged.

[0093] Comparative Example 8 The difference from Example 1 is that the total pore volume is selected as 0.8 cm³ based on the formula. 3 The porous carbon substrate of / g was replaced with a total pore volume of 0.65 cm³ calculated based on the relationship. 3 / g porous carbon substrate, the rest remain unchanged.

[0094] Comparative Example 9 The difference from Example 1 is that the gas flow rate of 0.15 L / min, temperature of 580°C, time of 1 h, and 3 nm coated carbon layer (a carbon layer with a porosity of 50% and a pore size of 20 nm) in step S4 is replaced with a gas flow rate of 0.10 L / min, temperature of 580°C, time of 1 h, and 3 nm coated carbon layer (a carbon layer with a porosity of 50% and a pore size of 20 nm), while the rest remain unchanged.

[0095] Comparative Example 10 The difference from Example 1 is that the carbon coating layer (a carbon layer with a porosity of 50% and a pore size of 20nm) with a gas flow rate of 0.15L / min, a temperature of 580°C, a time of 1h, and a 3nm diameter in step S4 is replaced with a carbon coating layer (a carbon layer with a porosity of 50% and a pore size of 50nm) with a gas flow rate of 0.20L / min, a temperature of 580°C, a time of 1h, and a 3nm diameter; all other parameters remain the same.

[0096] The silicon-carbon anode materials prepared in Examples 1-7 and Comparative Examples 1-10 were tested for various performance indicators. Anode sheets were prepared by mixing graphite with 20% silicon-carbon anode material, and then assembled with lithium cobalt oxide (LCO) cathode sheets to form lithium-ion batteries with a system voltage of 4.53V. The lithium-ion batteries were then subjected to low-temperature cycling and thickness expansion rate tests, and the experimental data are shown in Table 1 below. Among them, the low temperature cycling test: the low temperature cycling test was carried out at 0℃ and 10℃ with a rate of 0.34C in the voltage range of 4.53V-2.75V, and the capacity retention rate was recorded after 200 cycles.

[0097] Thickness expansion rate test: Measure the initial thickness T0 of the battery before cycling, and the thickness T1 under full charge state after 200 cycles. Expansion rate = (T1-T0) / T0×100%.

[0098] Table 1 A comparison of Examples 1-7 and Comparative Examples 1-2 in the table above shows that when the silane concentration in Examples 1-7 is 10%-30% of the mixed gas concentration, the silane flow rate is 15L / min-80L / min, the mixed gas velocity is 0.2m / s-0.3m / s, the deposition reaction temperature is 500℃-700℃, the silicon deposition time is 4h-8h, and the silicon deposition pressure is 5kPa-6kPa, it is beneficial to prepare silicon-carbon anode materials with high capacity, excellent low-temperature cycling performance, and low expansion characteristics. The comprehensive indicators of Examples 1-7 are significantly better than those of Comparative Examples 1-2, among which the comprehensive indicators of Example 1 are the best.

[0099] A comparison of Example 1 and Comparative Examples 3-4 shows that the phenolic resin carbon in Example 1 has a specific surface area of ​​1500 m². 2 / g-2000m 2 When the ratio was / g, the overall performance of Example 1 was significantly better than that of Comparative Examples 3-4.

[0100] As can be seen from the comparison between Example 1 and Comparative Examples 5-6, since the D50 particle size of the silicon-carbon anode material in Example 1 is between 7.5 μm and 9.5 μm, the overall performance of Example 1 is significantly better than that of Comparative Examples 5-6.

[0101] As can be seen from the comparison between Example 1 and Comparative Examples 7-8, the porous carbon substrate of Example 1 has a decreasing micropore density and an increasing mesopore density from the inside to the outside. When sufficient pore volume is selected according to the relationship formula, the comprehensive index of Example 1 is significantly better than that of Comparative Examples 7-8. It also makes it easier for operators to quickly select a suitable porous carbon substrate.

[0102] A comparison of Example 1 and Comparative Examples 9-10 shows that, due to the carbon source gas flow rate of Example 1 being 0.1L / min-0.2L / min, the carbon coating temperature being 500℃-600℃, and the time being 1h-2h, it is beneficial to form a coated carbon layer with a porosity of 40%-60% and a pore size of 2nm-50nm, thereby achieving the confinement effect on silicon particles. As a result, the overall performance of Example 1 is significantly better than that of Comparative Examples 9-10.

[0103] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is formed by vapor deposition of silicon within a porous carbon substrate, and the silicon-carbon anode material satisfies the following conditions: The D50 particle size of the silicon-carbon anode material is E, which satisfies 7.0μm≤E≤8.5μm; The silicon content in the silicon-carbon anode material is H, satisfying 50% ≤ H ≤ 57%; The tap density of the silicon-carbon anode material is TD, which satisfies 0.95 g / cm³. 3 ≤TD≤1.10g / cm 3 ; The specific surface area S of the silicon-carbon anode material satisfies 1.0 m². 2 / g≤S≤1.5m 2 / g; Furthermore, E, H, TD, and S simultaneously satisfy the following relationship: Relationship I: 9 ≤ (S × E) ≤ 12.75; Relationship II: 50 ≤ (H × TD) ≤ 60; Relation III: 11.20≤(100×TD / E)≤15.

71.

2. The silicon-carbon anode material according to claim 1, characterized in that, The relation I satisfies: 10 ≤ (S × E) ≤ 12.5; and / or, The relation II satisfies: 52 ≤ (H × TD) ≤ 58; and / or, The relation III satisfies: 12≤(100×TD / E)≤15.

3. The silicon-carbon anode material according to claim 1, characterized in that, The resistivity of the silicon-carbon anode material is R, which satisfies 0.4Ω·cm≤R≤0.9Ω·cm.

4. The silicon-carbon anode material according to claim 1, characterized in that, The silicon source gas flow rate during vapor deposition is 15 L / min–80 L / min, and the silicon deposition time is 4 h–8 h; and / or, The deposition temperature for silicon is 500℃-700℃; and / or, The deposition pressure for silicon is 5 kPa-6 kPa.

5. The silicon-carbon anode material according to claim 1, characterized in that, During vapor deposition, the gas velocity of the mixed gas is 0.2 m / s–0.3 m / s; and / or, During vapor deposition, the silicon source accounts for 10%-30% of the volume concentration of the mixed gas.

6. The silicon-carbon anode material according to claim 1, characterized in that, The porous carbon substrate has a D50 particle size of 7.5 μm-9.5 μm; and / or, The specific surface area of ​​the porous carbon substrate is 1500 m². 2 / g-2000m 2 / g.

7. The silicon-carbon anode material according to claim 1, characterized in that, The porous carbon substrate includes at least one of petroleum coke-based activated carbon, resin carbon, and biomass carbon.

8. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: The carbon precursor was pretreated to obtain a porous carbon substrate; The porous carbon substrate was placed in a vapor deposition reactor, and a silicon source was introduced to react with an inert gas to obtain a primary composite material. Carbon is coated onto the vapor deposition reactor using a carbon source gas to obtain the silicon-carbon anode material as described in any one of claims 1-7.

9. A negative electrode sheet, characterized in that, The silicon-carbon anode material included in any one of claims 1-7.

10. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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