Preparation method of silicon-carbon composite negative electrode material, silicon-carbon composite negative electrode material and application

Abstract

The application relates to a preparation method of a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material and application, wherein the silicon-carbon composite negative electrode material comprises a composite substrate and nano silicon particles loaded on the composite substrate; the composite substrate comprises a porous carbon substrate and an interface layer stacked on the porous carbon substrate; the interface layer comprises a first interface layer and a second interface layer which are stacked; the first interface layer does not contain carbon and silicon; the first interface layer and the second interface layer are connected through at least a chemical bond; the elastic modulus of the first interface layer is E, E is greater than or equal to 150 GPa; and the work function of the second interface layer is Phi, Phi is less than or equal to 4.9 eV. The silicon-carbon composite negative electrode material has excellent rate performance and cycle stability.

Description

Technical Field

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

[0002] In traditional silicon-carbon anode materials, direct contact between silicon and carbon easily triggers interfacial side reactions, generating a large amount of silicon carbide and producing irreversible capacity, which seriously affects the electrochemical activity of silicon-carbon anode materials. At the same time, the conductivity and mechanical support of carbon materials are insufficient to completely suppress the volume expansion of silicon, causing it to experience severe volume expansion during charge-discharge cycles, thereby affecting the cycle stability and rate performance of silicon-carbon anode materials. Summary of the Invention

[0003] Therefore, it is necessary to provide a method for preparing silicon-carbon composite anode material, the silicon-carbon composite anode material itself, and its applications to address the above problems. This silicon-carbon composite anode material has excellent rate performance and cycle stability.

[0004] A silicon-carbon composite anode material includes a composite substrate and nano-silicon particles loaded on the composite substrate. The composite substrate includes a porous carbon substrate and an interface layer stacked on the porous carbon substrate. The interface layer includes a first interface layer and a second interface layer stacked on top of each other. The first interface layer and the second interface layer are connected by at least chemical bonds. The first interface layer does not contain carbon or silicon. The elastic modulus of the first interface layer is E, where E ≥ 150 GPa. The work function of the second interface layer is Φ, where Φ ≤ 4.9 eV.

[0005] In one embodiment, when 150 GPa ≤ E < 200 GPa, Φ = 4.3 + 0.003 (E - 150); or when E ≥ 200 GPa, 4.6 eV ≤ Φ ≤ 4.9 eV.

[0006] In one embodiment, the interface layer further satisfies at least one of the following conditions:

[0007] (1) The interface layer comprises a first interface layer and a second interface layer sequentially stacked on the porous carbon substrate;

[0008] (2) The interface layer is at least partially disposed in the pores of the porous carbon substrate;

[0009] (3) The thickness of the interface layer is 2nm-4nm;

[0010] (4) The difference between the contact potential of the first interface layer and the work function of the second interface layer is ≤0.7;

[0011] (5) The contact resistance of the second interface layer is ≤20Ω·cm²;

[0012] (6) The thickness of the first interface layer is 1nm-2nm;

[0013] (7) The thickness of the second interface layer is 1nm-2nm;

[0014] (8) The first interface layer includes at least one of boron, nitrogen, phosphorus or sulfur;

[0015] (9) The second interface layer includes at least one of tungsten, molybdenum, tantalum, titanium, nickel, aluminum, zinc, manganese, tin, germanium, silver, gallium and magnesium.

[0016] In one embodiment, the porous carbon substrate further satisfies at least one of the following conditions:

[0017] (1) The pore size distribution of the porous carbon substrate has a mesopore ratio > 80%;

[0018] (2) The specific surface area of ​​the porous carbon substrate is 200 m² / g-2000 m² / g;

[0019] (3) The total pore volume of the porous carbon substrate is 0.4 cm³ / g-2.0 cm³ / g;

[0020] (4) The pore size distribution of the porous carbon substrate satisfies the following conditions: micropores ≤ 10%, mesopores ≥ 85%, and macropores ≤ 5%;

[0021] (5) The tap density of the porous carbon substrate is 0.05 g / cm³-3 g / cm³;

[0022] (6) The D of the porous carbon substrate 50 For 100nm-12µm, D 10 70nm-4μm, D 90 It is 150nm-16μm.

[0023] In one embodiment, the silicon-carbon composite anode material further satisfies at least one of the following conditions:

[0024] (1) The surface of the silicon-carbon composite anode material is further coated with a carbon coating layer, wherein the thickness of the carbon coating layer is 5nm-20nm;

[0025] (2) The surface of the silicon-carbon composite anode material is further coated with a carbon coating layer, wherein the ID / IG value of the carbon coating layer is <0.8;

[0026] (3) The mass fraction of the nano-silicon particles in the silicon-carbon composite anode material is 30%-70%;

[0027] (4) The silicon carbide content in the silicon-carbon composite anode material is <1 at%;

[0028] (5) The particle size of the nano-silicon particles is 10nm-50nm.

[0029] The silicon-carbon composite anode material of the present invention, by employing a porous carbon substrate, utilizes the high specific surface area and excellent pore structure of porous carbon to alleviate the volume expansion problem of silicon during charge and discharge, and promotes lithium-ion diffusion, thereby improving the cycle stability and rate performance of the anode material. Simultaneously, by setting an interface layer, comprising a first interface layer and a second interface layer stacked together, the first and second interface layers are connected by at least chemical bonds, and the elastic modulus of the first interface layer and the work function of the second interface layer are defined. This not only serves as a physical barrier layer, effectively preventing the formation of irreversible silicon carbide byproducts between the porous carbon substrate and the nano-silicon particles, reducing irreversible capacity generation and improving the electrochemical activity of the anode material, but also utilizes the first interface layer to provide high compressive strength, dispersing silicon expansion stress and effectively regulating the volume expansion problem of silicon during charge and discharge, while the second interface layer reduces the interfacial contact resistance between the nano-silicon particles and the porous carbon substrate and improves charge transfer capability, thereby significantly improving the cycle stability and rate performance of the silicon-carbon composite anode material. Therefore, the silicon-carbon composite anode material of the present invention exhibits excellent cycle stability and rate performance.

[0030] A method for preparing the silicon-carbon composite anode material includes the following steps:

[0031] Provides porous carbon substrates;

[0032] A first interface layer and a second interface layer were deposited on a porous carbon substrate using chemical vapor deposition to construct an interface layer, thereby obtaining a composite substrate. The deposition temperature was 400℃-650℃.

[0033] Silicon nanoparticles are deposited on the composite substrate to obtain a silicon-carbon composite anode material.

[0034] In one embodiment, during the step of preparing the composite substrate, at least one of the following conditions is also met:

[0035] (1) The temperature for depositing the first interface layer is 550℃-650℃, the pressure is 50Pa-200Pa, and the deposition time is 10min-30min;

[0036] (2) The temperature for depositing the second interface layer is 400℃-500℃, the pressure is 100Pa-300Pa, and the deposition time is 5min-15min;

[0037] (3) An interface layer is constructed by sequentially depositing a first interface layer and a second interface layer on a porous carbon substrate using chemical vapor deposition.

[0038] (4) The pore size distribution of the porous carbon substrate has a mesopore ratio of >80%.

[0039] In one embodiment, the method for preparing the silicon-carbon composite anode material further satisfies at least one of the following conditions:

[0040] (1) The preparation method of the silicon-carbon composite anode material further includes the following steps: performing carbon coating treatment on the surface of the silicon-carbon composite anode material to form a carbon coating layer, wherein the ID / IG value of the carbon coating layer is <0.8;

[0041] (2) Nano-silicon particles are deposited on the composite substrate by chemical vapor deposition, wherein the deposition temperature is 350℃-600℃ and the volume ratio of silane gas to hydrogen gas is 1:5-1:10.

[0042] In the preparation method of the silicon-carbon composite anode material of the present invention, a uniformly thick interface layer is constructed by uniformly depositing a first interface layer with a specific elastic modulus and a second interface layer with a specific work function on a porous carbon substrate, and the first interface layer and the second interface layer are connected by chemical bonds. At the same time, by controlling the deposition temperature, the thickness of the interface layer can be precisely controlled, so that the interface layer has a thinner thickness, avoiding clogging the pores of the porous carbon substrate, not affecting the electron transport channels, and better inducing the deposition of nano-silicon particles on the composite substrate. Moreover, the presence of the interface layer can effectively inhibit the reaction of nano-silicon particles with the porous carbon substrate during the deposition process to form silicon carbide.

[0043] A negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on the surface of the current collector, the composition of the negative electrode active layer comprising the silicon-carbon composite negative electrode material.

[0044] A secondary battery including the aforementioned negative electrode. Detailed Implementation

[0045] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0046] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0047] The silicon-carbon composite anode material provided by the present invention includes a composite substrate and nano-silicon particles loaded on the composite substrate. The composite substrate includes a porous carbon substrate and an interface layer stacked on the porous carbon substrate. The interface layer includes a first interface layer and a second interface layer stacked on top of each other. The first interface layer and the second interface layer are connected by chemical bonds. The first interface layer does not contain carbon or silicon. The elastic modulus of the first interface layer is E, where E ≥ 150 GPa. The work function of the second interface layer is Φ, where Φ ≤ 4.9 eV.

[0048] In the silicon-carbon composite anode material of the present invention, a composite substrate comprising a porous carbon substrate and an interface layer stacked on the porous carbon substrate is provided. The porous carbon, with its high specific surface area and excellent pore structure, ensures efficient deposition of the interface layer and silicon nanoparticles. Furthermore, it provides a buffer space for the volume expansion of the silicon nanoparticles during charging and discharging, reducing expansion stress by 40% and alleviating the volume expansion problem of silicon. Simultaneously, it promotes lithium-ion diffusion, and the diffusion coefficient is greater than […]. cm² / s is beneficial for improving the cycle stability and rate performance of silicon-carbon composite anode materials.

[0049] Meanwhile, by setting an interface layer comprising a first interface layer and a second interface layer stacked together, with the first and second interface layers connected by at least chemical bonds, and defining the elastic modulus of the first interface layer and the work function of the second interface layer, the interface layer is endowed with the following three functions: First, as a physical barrier layer between the porous carbon substrate and the nano-silicon particles, it effectively prevents the formation of irreversible silicon carbide byproducts between the porous carbon substrate and the nano-silicon particles, reduces the generation of irreversible capacity, and improves the electrochemical activity of the anode material; Second, by utilizing the high elastic modulus of the first interface layer, it provides high compressive strength, disperses silicon expansion stress, avoids structural collapse, and effectively regulates the volume expansion of silicon during charging and discharging; Third, by utilizing the low work function and high electronic conductivity of the second interface layer, it can reduce the interfacial contact resistance between the nano-silicon particles and the porous carbon substrate while improving the charge transfer capability; thereby significantly improving the cycle stability and rate performance of the silicon-carbon composite anode material. Moreover, since the first and second interface layers are connected by at least chemical bonds, the bonding force between the interface layers is improved, which can effectively suppress the delamination of the interface layer during the cycling process of the silicon-carbon composite anode material, improve the stability of the interface layer, and further improve the cycling stability of the silicon-carbon composite anode material.

[0050] Therefore, the silicon-carbon composite anode material of the present invention exhibits excellent cycle stability and rate performance through the synergistic effect of the porous carbon substrate and the interface layer with a specific structure. Optionally, the interface layer is at least partially disposed in the pores of the porous carbon substrate. It is understood that the interface layer may be disposed only in the pores of the porous carbon substrate, or the interface layer may be disposed in both the pores and the surface of the porous carbon substrate, preferably the interface layer is disposed in both the pores and the surface of the porous carbon substrate.

[0051] In this invention, the porous carbon substrate has a hierarchical pore structure, including micropores, mesopores, and macropores, with mesopores being the predominant structure. Optionally, the pore size distribution of the porous carbon substrate has a mesopore ratio > 80%. Further, the pore size distribution of the porous carbon substrate satisfies the following: micropore ratio ≤ 10%, mesopore ratio ≥ 85%, and macropore ratio ≤ 5%. Specifically, the micropore diameter is < 2.0 nm, the mesopore diameter is 2 nm-50 nm, and the macropore diameter is > 50 nm. This configuration allows for the control of the pore size distribution of the porous carbon substrate, which helps reduce pore resistance, improve the loading efficiency of silicon nanoparticles, and provide sufficient buffer space to better regulate the volume expansion of silicon nanoparticles during charging and discharging, and promote lithium-ion diffusion, thereby further improving the electrochemical performance of the silicon-carbon composite anode material.

[0052] Optionally, the specific surface area of ​​the porous carbon substrate is 200 m² / g-2000 m² / g, preferably 500 m² / g-2000 m² / g; specifically, the specific surface area of ​​the porous carbon substrate includes, but is not limited to, 500 m² / g, 600 m² / g, 800 m² / g, 1000 m² / g, 1200 m² / g, 1400 m² / g, 1600 m² / g, 1800 m² / g, and 2000 m² / g.

[0053] Optionally, the total pore volume of the porous carbon substrate is 0.4 cm³ / g to 2.0 cm³ / g; specifically, the total pore volume of the porous carbon substrate includes, but is not limited to, 0.4 cm³ / g, 0.5 cm³ / g, 0.6 cm³ / g, 0.7 cm³ / g, 0.8 cm³ / g, 0.9 cm³ / g, 1.0 cm³ / g, 1.2 cm³ / g, 1.3 cm³ / g, 1.5 cm³ / g, 1.6 cm³ / g, 1.7 cm³ / g, 1.8 cm³ / g, and 2.0 cm³ / g. This configuration is beneficial for increasing the loading of silicon nanoparticles.

[0054] Optionally, the D of the porous carbon substrate 50 For 100nm-12µm, D 10 70nm-4μm, D 90 The wavelength is 150nm-16μm, preferably D. 503μm-8µm, D 10 The diameter is 1μm-4μm, D 90 It is 10μm-15μm.

[0055] The porous carbon substrate of the present invention, under the specific surface area, total pore volume and particle size range mentioned above, can ensure good structural stability while facilitating the loading of nano-silicon particles, which is beneficial to improving the capacity and cycle performance of silicon-carbon composite anode materials.

[0056] Optionally, the tap density of the porous carbon substrate is 0.05 g / cm³-3 g / cm³, preferably 0.1 g / cm³-2 g / cm³; this setting is beneficial to improving the energy density of the battery.

[0057] The applicant discovered through research that there is a specific relationship between the elastic modulus E of the first interface layer and the work function Φ of the second interface layer, which enables the two to fully exert their synergistic effect and better balance the relationship between the volume expansion and charge transport efficiency of the silicon-carbon composite anode material. Specifically, when 150GPa≤E<200GPa, Φ=4.3+0.003(E-150); when E≥200GPa, 4.6eV≤Φ≤4.9eV. It is understandable that, based on the corresponding relationship above, the work function Φ of the second interface layer can be adjusted according to the elastic modulus E of the first interface layer. By selecting a second interface layer with a suitable work function to match the first interface layer, the first interface layer can provide better mechanical support and stress buffering, effectively suppressing the volume expansion of silicon and preventing structural collapse. At the same time, it makes the work function of the second interface layer match the contact potential (work function) of silicon and carbon (ΦSi≈4.3eV, ΦC≈5.0eV), reducing the interface barrier and promoting charge transfer to compensate for the influence of interface stress on electron transport, thereby further improving the cycle stability and rate performance of silicon-carbon composite anode materials.

[0058] It should be noted that when 150GPa≤E<200GPa, in the relationship between the elastic modulus E of the first interface layer and the work function of the second interface layer Φ, only the magnitude of the value is involved in the calculation of the work function of the second interface layer, and the conversion of units is not involved. In addition, the unit of the work function of the second interface layer in this invention is eV.

[0059] Optionally, the difference between the contact potential of the first interface layer and the work function of the second interface layer is ≤0.7. This setting enables the formation of a band gradient between the first and second interface layers, reduces the interface barrier, and improves electron mobility, which is beneficial to further improve the rate performance of silicon-carbon composite anode materials.

[0060] In this invention, the first interface layer and the second interface layer are connected by chemical bonds, wherein the bond energy of the chemical bonds is >460kJ / mol; this setting is beneficial to ensure that the first interface layer and the second interface layer have high bonding force, improve the stability of the interface layer, effectively suppress interface delamination during cycling, and further improve the cycling stability of silicon-carbon composite anode material.

[0061] In this invention, the interface layer comprises a first interface layer and a second interface layer sequentially stacked on the porous carbon substrate, or the interface layer comprises a second interface layer and a first interface layer sequentially stacked on the porous carbon substrate, preferably the interface layer comprises a first interface layer and a second interface layer sequentially stacked on the porous carbon substrate. This configuration, by controlling the order in which the first and second interface layers are placed, allows the first interface layer to be placed on the porous carbon substrate (i.e., on the pores and surface of the porous carbon substrate) as a stress-buffering substrate, and then the second interface layer is placed. This optimizes the interface charge transport capability, effectively ensuring the mechanical support and electron transport efficiency of the interface layer, while also better inducing the uniform deposition of nano-silicon particles on the pores and surface of the porous carbon substrate.

[0062] Optionally, the thickness of the interface layer is 2nm-4nm; this setting can better avoid pore blockage of the porous carbon substrate by adjusting the thickness of the interface layer, and the pore closure rate is <5%, thereby better avoiding the influence of the interface layer on the electron transport channel, while facilitating better induction of nano-silicon particles to deposit on the interface layer.

[0063] Optionally, the thickness of the first interface layer is 1nm-2nm; the thickness of the second interface layer is 1nm-2nm. With this setting, the thickness of the interface layer can be controlled by adjusting the thickness of the first interface layer and the thickness of the second interface layer, which can better avoid clogging the pores of the porous carbon substrate and not affect the electron transport channels.

[0064] Optionally, the contact resistance of the second interface layer is ≤20Ω·cm². This setting enables a low interfacial contact resistance between the porous carbon substrate and the nano-silicon particles, which is beneficial to further improve electron transport efficiency and rate performance of silicon-carbon composite anode materials.

[0065] Optionally, the first interface layer includes at least one of boron, nitrogen, phosphorus or sulfur; the second interface layer includes at least one of tungsten, molybdenum, tantalum, titanium, nickel, aluminum, zinc, manganese, tin, germanium, silver, gallium and magnesium.

[0066] Optionally, the mass fraction of the nano-silicon particles in the silicon-carbon composite anode material is 30%-70%; this setting is beneficial to improving the electrochemical performance of the silicon-carbon composite anode material.

[0067] Optionally, the particle size of the silicon nanoparticles is 10nm-50nm; specifically, the particle size of the silicon nanoparticles includes, but is not limited to, 10nm, 20nm, 30nm, 40nm, and 50nm. This configuration results in the silicon nanoparticles having a high specific surface area and a short diffusion path, which is beneficial for improving the electrochemical performance of silicon-carbon composite anode materials.

[0068] In this invention, the surface of the silicon-carbon composite anode material is further coated with a carbon coating layer. This configuration has two advantages: firstly, it facilitates the construction of a complete conductive network, further improving the electronic conductivity and rate performance of the silicon-carbon composite anode material; secondly, it further protects the silicon nanoparticles and the silicon-carbon composite anode material, preventing them from contacting the electrolyte. Simultaneously, it can work in conjunction with the porous carbon substrate and the first interface layer to better regulate the volume expansion of the silicon nanoparticles, further improving the cycle performance of the silicon-carbon composite anode material and the battery.

[0069] Furthermore, the ID / IG value of the carbon coating layer is <0.8. This setting helps to further improve the conductivity of the carbon coating layer (conductivity >120S / cm) while reducing the surface defect density (defect density <5×10). 3 μm -2 This reduces side reactions in the electrolyte, thereby further improving the rate performance of silicon-carbon composite anode materials and batteries.

[0070] Optionally, the thickness of the carbon coating layer is 5nm-20nm; specifically, the thickness of the carbon coating layer includes, but is not limited to, 5nm, 6nm, 7nm, 10nm, 12nm, 14nm, 16nm, 18nm, 19nm, and 20nm. This configuration is beneficial for improving the electronic conductivity of the silicon-carbon composite anode material, thereby further improving the rate performance of the battery.

[0071] In this invention, the silicon carbide content in the silicon-carbon composite anode material is <1 at%, preferably ≤0.5 at; this setting results in the silicon-carbon composite anode material having low silicon carbide content, reducing the generation of irreversible capacity, and is beneficial to improving the electrochemical activity of the silicon-carbon composite anode material.

[0072] Meanwhile, the present invention also provides a method for preparing the silicon-carbon composite anode material, comprising the following steps:

[0073] S1 provides a porous carbon substrate.

[0074] In step S1, the pore size distribution of the porous carbon substrate has a mesopore ratio of >80%. It can be understood that the porous carbon substrate is mainly composed of mesopore structure, which facilitates the uniform deposition of the first interface layer and the second interface layer in subsequent step S2 and the nano-silicon particles in step S3.

[0075] In this invention, the porous carbon substrate can be obtained by purchasing from the market or by preparing it by a specific method. The method for preparing the porous carbon substrate is not particularly limited. Specifically, in one embodiment, the porous carbon substrate can be prepared by a soft template method or a hard template method, preferably by a soft template method.

[0076] In one embodiment, the specific steps for preparing a porous carbon substrate using the soft template method are as follows:

[0077] The template agent, carbon precursor and solvent are mixed and then evaporation-induced self-assembly is carried out to form an ordered mesoporous structure to obtain pre-prepared porous carbon.

[0078] The pre-prepared porous carbon is carbonized under an inert atmosphere, and then the template agent is removed by acid washing to obtain a porous carbon substrate.

[0079] In this invention, the pore structure of the porous carbon substrate can be adjusted by changing the molecular weight of the template agent and the mass ratio of the template agent to the carbon precursor. Specifically, the mass ratio of the template agent to the carbon precursor is 1:5 to 1:20.

[0080] Further, the template agent is selected from at least one of F127 (polyoxyethylene polyoxypropylene ether block copolymer), P123 (polyethylene oxide-polyoxypropylene oxide-polyethylene oxide triblock copolymer), or an amphiphilic surfactant; the carbon precursor is selected from at least one of phenolic resin, glucose, sucrose, polyacrylonitrile (PAN), or pitch, preferably phenolic resin.

[0081] In one embodiment, the mass ratio of the carbon precursor to the solvent is 1:5 to 1:10; wherein the solvent is selected from at least one of methanol and ethanol.

[0082] In one embodiment, the carbonization process includes: heating to 800℃-1200℃ at a rate of 2℃ / min-5℃ / min, and carbonization time of 1h-3h.

[0083] In one embodiment, during the pickling process, the mass concentration of the acid solution is 10%-30%, wherein the acid solution is selected from inorganic acid solutions or oxalic acid solutions.

[0084] In this invention, the porous carbon substrate prepared by the above preparation method has an ordered mesoporous structure. Specifically, the porous carbon substrate has a pore size distribution with a mesoporous ratio of >90%, a specific surface area of ​​200m² / g-2000m² / g, a pore size of 2nm-100nm, and a tap density of 0.1g / cm³-2g / cm³.

[0085] S2, depositing a first interface layer and a second interface layer on a porous carbon substrate to construct an interface layer, thereby obtaining a composite substrate, wherein the deposition temperature is 400℃-650℃.

[0086] It is understood that in step S2, the first interface layer and the second interface layer are uniformly deposited on the pores and / or surface of the porous carbon substrate, and the first interface layer and the second interface layer are connected by at least chemical bonds to construct an interface layer with good adhesion and uniform thickness. This interface layer and the porous carbon substrate together constitute a composite substrate. At the same time, by controlling the deposition temperature, the thickness of the interface layer can be precisely controlled, so that the interface layer has a thinner thickness, avoiding clogging the pores of the porous carbon substrate, without affecting the electron transport channels, while better inducing the uniform deposition of nano-silicon particles on the composite substrate in the subsequent step S3. Moreover, the presence of the interface layer can effectively inhibit the reaction of nano-silicon particles with the porous carbon substrate during the deposition process to form silicon carbide.

[0087] It is understood that in step S2, the first interface layer does not contain carbon and silicon, the elastic modulus of the first interface layer is E, E≥150GPa, and the work function of the second interface layer is Φ, Φ≤4.9eV.

[0088] Optionally, the temperature for depositing the first interface layer is 550℃-650℃, the pressure is 50Pa-200Pa, and the deposition time is 10min-30min; such settings are beneficial for forming a first interface layer with uniform thickness, which can be used to disperse silicon expansion stress.

[0089] Optionally, the temperature for depositing the second interface layer is 400℃-500℃, the pressure is 100Pa-300Pa, and the deposition time is 5min-15min. This setting is beneficial for forming a second interface layer with uniform thickness and a contact resistance of ≤20Ω·cm², thus optimizing charge transport.

[0090] In this invention, the deposition method for constructing the interface layer by depositing the first interface layer and the second interface layer on the porous carbon substrate is not particularly limited, but the preferred method is chemical vapor deposition.

[0091] In this invention, the order in which the first and second interface layers are deposited on the porous carbon substrate is not particularly limited. Specifically, the first and second interface layers are deposited sequentially on the porous carbon substrate to construct the interface layer; or, the second and first interface layers are deposited sequentially on the porous carbon substrate to construct the interface layer. Preferably, the first and second interface layers are deposited sequentially on the porous carbon substrate to construct the interface layer. This arrangement helps to improve the structural stability of the interface layer, suppress delamination during cycling, and further improve the cycling stability of the silicon-carbon composite anode material.

[0092] It should be noted that in this invention, during step S2, in the process of depositing the first interface layer or the second interface layer on the porous carbon substrate, in addition to physical adsorption, the first interface layer or the second interface layer and the porous carbon substrate will also undergo in-situ bonding to form chemical bonds, thereby improving the bonding force between the porous carbon substrate and the interface layer, and thus improving the interlayer bonding force of the composite substrate.

[0093] Optionally, the material of the first interface layer includes at least one of boron, nitrogen, phosphorus, or sulfur, preferably boron; the material of the second interface layer includes at least one of tungsten, molybdenum, tantalum, titanium, nickel, aluminum, zinc, manganese, tin, germanium, silver, gallium, and magnesium, preferably tungsten, molybdenum, tantalum, titanium, or nickel. This configuration, on the one hand, better ensures that the bond energy of the chemical bonds formed between the deposited first and second interface layers is >460 kJ / mol, improving the interlayer bonding force of the interface layers and further enhancing the cycle stability of the silicon-carbon composite anode material. On the other hand, it allows the constructed interface layer to effectively physically isolate the silicon, preventing irreversible bonding. Simultaneously, the material of the second interface layer, during deposition, not only avoids extensive irreversible bonding with silicon, facilitating the subsequent deposition of nano-silicon particles, but also possesses good conductivity and chemical stability, effectively improving the electronic conductivity and structural stability of the interface layer, which is beneficial for further improving the rate performance and cycle stability of the silicon-carbon composite anode material.

[0094] It is understood that the interface layer contains compounds or single elements composed of non-metallic elements such as boron, nitrogen, phosphorus or sulfur and metallic elements such as tungsten, molybdenum, tantalum, titanium, nickel, aluminum, zinc, manganese, tin, germanium, silver, gallium and magnesium.

[0095] S3, depositing nano-silicon particles on the composite substrate to obtain a silicon-carbon composite anode material.

[0096] In this invention, nano-silicon particles can be deposited on the composite substrate using chemical vapor deposition, physical vapor deposition, or sol-gel methods, with chemical vapor deposition being the preferred method.

[0097] In this process, when depositing silicon nanoparticles on the composite substrate using chemical vapor deposition, the deposition temperature is 350℃-600℃, and the volume ratio of silane gas to hydrogen gas is 1:5-1:10. This configuration facilitates the uniform deposition of silicon nanoparticles on the composite substrate.

[0098] In this invention, the preparation method of the silicon-carbon composite anode material further includes the following step: performing a carbon coating treatment on the surface of the silicon-carbon composite anode material to form a carbon coating layer, wherein the ID / IG value of the carbon coating layer is <0.8. This configuration facilitates the better construction of a complete conductive network, improves the rate performance of the silicon-carbon composite anode material, protects the nano-silicon particles and the silicon-carbon composite anode material, prevents them from contacting the electrolyte, and further improves the cycle performance of the silicon-carbon composite anode material.

[0099] In this invention, the preparation method of the carbon coating layer is not particularly limited. In one embodiment, a carbon coating layer is formed by chemical vapor deposition on the surface of the silicon-carbon composite negative electrode material. During the deposition process, the temperature is 500℃-900℃, and the carbon source is selected from C2H2, C3H6 or biomass carbon source. The biomass carbon source is preferably lignin.

[0100] In addition, the present invention also provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on the surface of the current collector, wherein the composition of the negative electrode active layer comprises the silicon-carbon composite negative electrode material as described above.

[0101] A secondary battery comprising the aforementioned negative electrode. This battery exhibits both excellent cycle stability and rate performance.

[0102] The following specific embodiments will further illustrate the preparation method, application, and use of the silicon-carbon composite anode material. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without a specified manufacturer are all commercially available conventional products. It should also be noted that the specific surface area, pore volume, and pore size distribution of the porous carbon substrates involved in the embodiments and comparative examples of this invention were obtained using the Micromeritics ASAP2460 BET method. The thicknesses of the first and second interface layers were measured using TEM or AFM. The content of non-metallic elements (e.g., nitrogen) doped in the first interface layer was tested using XPS depth analysis, with test conditions of Al Kα rays (1486.6 eV) and a sputtering rate of 0.1 nm / s. The mass fraction of nano-silicon particles in the silicon-carbon composite anode material was obtained using thermogravimetric analysis (TGA).

[0103] Example 1

[0104] Template agent F127, phenolic resin (manufacturer: Shengquan, model: 2893B, molecular weight: 800), and 50 mL of anhydrous ethanol were mixed and magnetically stirred for 6 h. The mixture was then transferred to a petri dish and allowed to self-assemble into an ordered mesoporous structure at 40 °C for 48 h by solvent evaporation, yielding pre-prepared porous carbon. The mass ratio of template agent F127 to phenolic resin was 1:5. The pre-prepared porous carbon was then carbonized in a nitrogen atmosphere at a rate of 3 °C / min to 1000 °C for 2 h. Subsequently, the template agent F127 was removed by acid washing with 5% HF to obtain a porous carbon substrate. The porous carbon substrate has a D... 50 It is 6.2 μm, D 10 It is 3.4 μm, D 90 The surface area is 13.6 μm, the specific surface area is 850 m² / g, the total pore volume is 0.8 cm³ / g, the tap density is 0.8 g / cm³, and the pore size distribution meets the following requirements: micropores account for 5%, mesopores account for 90%, and macropores account for 5%.

[0105] A composite substrate was constructed by sequentially depositing a first interface layer (elastic modulus E of 400 GPa) and a second interface layer (work function Φ of 4.3 eV) on a porous carbon substrate using chemical vapor deposition (CVD). During the deposition of the first interface layer, the precursors were BCl3 and H2, with a flow rate of 50 sccm for both BCl3 and H2, a deposition temperature of 600℃, a pressure of 100 Pa, and a deposition time of 20 min. During the deposition of the second interface layer, the precursors were Al(CH3)3 and Ar, with a flow rate of 30 sccm for Al(CH3)3 and 200 sccm for Ar, a deposition temperature of 450℃, a pressure of 200 Pa, and a deposition time of 10 min. The thickness of the first interface layer was 1.5 nm, the thickness of the second interface layer was 1.2 nm, the contact resistance was 8 Ω·cm², and the total thickness of the interface layers was 2.7 nm. The difference between the contact potential of the first interface layer and the work function of the second interface layer was 0.4.

[0106] Nanoscale silicon particles were deposited on a composite substrate using chemical vapor deposition. The precursors were SiH4 and H2, with a SiH4 flow rate of 20 sccm and an H2 flow rate of 100 sccm. The deposition temperature was 550℃ and the deposition time was 60 min. The nanoscale silicon particles had a particle size of 10 nm.

[0107] A carbon coating layer was deposited on the outer surface of a porous carbon substrate with deposited silicon nanoparticles using chemical vapor deposition. During the deposition process, the precursors were C2H2 and Ar, with a C2H2 flow rate of 10 sccm and an Ar flow rate of 200 sccm. The deposition temperature was 700℃ and the deposition time was 30 min, resulting in a silicon-carbon composite anode material. The thickness of the carbon coating layer was 12 nm, the ID / IG ratio was 0.6, and the mass fraction of silicon nanoparticles in the silicon-carbon composite anode material was 50%.

[0108] Example 2

[0109] Template agent P123, phenolic resin (manufacturer: Shengquan, model: 2893B, molecular weight: 800), and 50 mL of anhydrous ethanol were mixed and magnetically stirred for 6 h. The mixture was then transferred to a petri dish and the solvent was evaporated at 40 °C for 48 h to form an ordered mesoporous structure, yielding pre-prepared porous carbon. The mass ratio of template agent P123 to phenolic resin was 1:15. The pre-prepared porous carbon was then carbonized in a nitrogen atmosphere at a rate of 3 °C / min to 900 °C for 2 h. Subsequently, the template agent P123 was removed by acid washing with 5% HF to obtain a porous carbon substrate. The porous carbon substrate has a D... 50 It is 6.9 μm, D 10 It is 2.1 μm, D 90 The surface area is 15.7 μm, the specific surface area is 850 m² / g, the total pore volume is 0.78 cm³ / g, the tap density is 1.0 g / cm³, and the pore size distribution meets the following requirements: micropores account for 3%, mesopores account for 92%, and macropores account for 5%.

[0110] A composite substrate was constructed by sequentially depositing a first interface layer (elastic modulus E = 180 GPa) and a second interface layer (work function Φ = 4.13 eV) on a porous carbon substrate using chemical vapor deposition (CVD). During the deposition of the first interface layer, the precursors were NH3 and Ar, with a flow rate of 100 sccm for NH3 and 150 sccm for Ar. The deposition temperature was 550 °C, the pressure was 150 Pa, and the deposition time was 30 min. During the deposition of the second interface layer, the precursor was Z... The flow rates of n(C2H5)2 and Ar, Zn(C2H5)2 were 20 sccm, the flow rate of Ar was 200 sccm, the deposition temperature was 400℃, the pressure was 100 Pa, and the deposition time was 15 min. The thickness of the first interface layer was 1 nm, and the nitrogen content in the first interface layer was 8.5 at%. The thickness of the second interface layer was 2 nm, the contact resistance was 12 Ω·cm², and the thickness of the interface layer was 3 nm. The difference between the contact potential of the first interface layer and the work function of the second interface layer was 0.61.

[0111] Nanoscale silicon particles were deposited on a composite substrate using chemical vapor deposition. The precursors were SiH4 and H2, with a SiH4 flow rate of 20 sccm and an H2 flow rate of 100 sccm. The deposition temperature was 550℃ and the deposition time was 60 min. The nanoscale silicon particles had a particle size of 10 nm.

[0112] A carbon coating layer was deposited on the outer surface of a porous carbon substrate with deposited silicon nanoparticles using chemical vapor deposition. During the deposition process, the precursors were C2H2 and Ar, with a C2H2 flow rate of 10 sccm and an Ar flow rate of 200 sccm. The deposition temperature was 700℃ and the deposition time was 30 min, resulting in a silicon-carbon composite anode material. The thickness of the carbon coating layer was 12 nm, the ID / IG ratio was 0.6, and the mass fraction of silicon nanoparticles in the silicon-carbon composite anode material was 50%.

[0113] Example 3

[0114] Template agent P123, sucrose (manufactured by Xilong Scientific, molecular weight 342.29), and 50 mL of anhydrous ethanol were mixed and magnetically stirred for 6 h. The mixture was then transferred to a petri dish, and the solvent was evaporated at 40 °C for 48 h to self-assemble into an ordered mesoporous structure, yielding pre-prepared porous carbon. The mass ratio of template agent P123 to sucrose was 1:5. The pre-prepared porous carbon was then carbonized in a nitrogen atmosphere at a rate of 3 °C / min to 950 °C for 2 h. Subsequently, template agent P123 was removed by acid washing with 5% HF to obtain a porous carbon substrate. The porous carbon substrate has a D... 50 It is 7.8 μm, D 10 It is 2.8μm, D 90 The pore size is 15μm, the specific surface area is 720m² / g, the total pore volume is 1.1cm³ / g, the tap density is 0.9g / cm³, and the pore size distribution meets the following requirements: micropores account for 9%, mesopores account for 87%, and macropores account for 4%.

[0115] A composite substrate was constructed by sequentially depositing a first interface layer (elastic modulus E = 170 GPa) and a second interface layer (work function Φ = 3.56 eV) on a porous carbon substrate using chemical vapor deposition (CVD). During the deposition of the first interface layer, the precursors were PH3 and Ar, with a PH3 flow rate of 50 sccm and an Ar flow rate of 150 sccm. The deposition temperature was 550 °C, the pressure was 120 Pa, and the deposition time was 30 min. During the deposition of the second interface layer, the precursor was M... The flow rates of g(Cp)2 and Ar, Mg(Cp)2 were 25 sccm, Ar was 200 sccm, the deposition temperature was 380℃, the pressure was 150 Pa, and the deposition time was 20 min. The thickness of the first interface layer was 1.5 nm, and the phosphorus content in the first interface layer was 6.8 at%. The thickness of the second interface layer was 1.5 nm, the contact resistance was 13 Ω·cm², and the thickness of the interface layer was 3 nm. The difference between the contact potential of the first interface layer and the work function of the second interface layer was 0.53.

[0116] Nanoscale silicon particles were deposited on a composite substrate using chemical vapor deposition. The precursors were SiH4 and H2, with a SiH4 flow rate of 20 sccm and an H2 flow rate of 100 sccm. The deposition temperature was 550℃ and the deposition time was 60 min. The nanoscale silicon particles had a particle size of 10 nm.

[0117] A carbon coating layer was deposited on the outer surface of a porous carbon substrate with deposited silicon nanoparticles using chemical vapor deposition. During the deposition process, the precursors were C2H2 and Ar, with a C2H2 flow rate of 10 sccm and an Ar flow rate of 200 sccm. The deposition temperature was 700℃ and the deposition time was 30 min, resulting in a silicon-carbon composite anode material. The thickness of the carbon coating layer was 12 nm, the ID / IG ratio was 0.6, and the mass fraction of silicon nanoparticles in the silicon-carbon composite anode material was 50%.

[0118] Example 4

[0119] Example 4 differs from Example 1 only in that SiO2 nanospheres (20 nm in diameter) were used as a template, and phenolic resin (manufacturer: Shengquan, model: 2893B, molecular weight: 800) was filled, carbonized at 850°C, and then etched with HF to obtain a porous carbon substrate. The porous carbon substrate has a D... 50 It is 7.5μm, D 10 It is 2.0 μm, D 90 The surface area is 14.2 μm, the specific surface area is 720 m² / g, the total pore volume is 1.3 cm³ / g, the tap density is 1.1 g / cm³, and the pore size distribution meets the following requirements: micropores account for 11%, mesopores account for 86%, and macropores account for 3%.

[0120] A composite substrate was constructed by sequentially depositing a first interface layer (elastic modulus E of 150 GPa) and a second interface layer (work function Φ of 4.16 eV) on a porous carbon substrate using chemical vapor deposition (CVD). During the deposition of the first interface layer, the precursors were H₂S and Ar, with a H₂S flow rate of 40 sccm and an Ar flow rate of 150 sccm. The deposition temperature was 500 °C, the pressure was 100 Pa, and the deposition time was 15 min. During the deposition of the second interface layer, the precursor was an aqueous solution of AgNO₃, the deposition temperature was 400 °C, the pressure was 180 Pa, and the deposition time was 10 min. The thickness of the first interface layer was 1.2 nm, and the sulfur content in the first interface layer was 4.2 at%. The thickness of the second interface layer was 2 nm, the contact resistance was 15 Ω·cm², and the thickness of the interface layer was 3.2 nm. The difference between the contact potential of the first interface layer and the work function of the second interface layer was 0.27.

[0121] Nanoscale silicon particles were deposited on a composite substrate using chemical vapor deposition. The precursors were SiH4 and H2, with a SiH4 flow rate of 20 sccm and an H2 flow rate of 100 sccm. The deposition temperature was 550℃ and the deposition time was 60 min. The nanoscale silicon particles had a particle size of 10 nm.

[0122] A carbon coating layer was deposited on the outer surface of a porous carbon substrate with deposited silicon nanoparticles using chemical vapor deposition. During the deposition process, the precursors were C2H2 and Ar, with a C2H2 flow rate of 10 sccm and an Ar flow rate of 200 sccm. The deposition temperature was 700℃ and the deposition time was 30 min, resulting in a silicon-carbon composite anode material. The thickness of the carbon coating layer was 12 nm, the ID / IG ratio was 0.6, and the mass fraction of silicon nanoparticles in the silicon-carbon composite anode material was 50%.

[0123] Example 5

[0124] Example 5 differs from Example 1 only in that a porous carbon substrate is impregnated with tetraethyl orthosilicate sol, then gelled with ammonia, and reduced at 600°C to obtain nano-silicon particles; all other conditions are the same to obtain a silicon-carbon composite anode material, wherein the mass fraction of nano-silicon particles in the silicon-carbon composite anode material is 45%.

[0125] Example 6

[0126] Example 6 differs from Example 1 only in that a first interface layer (elastic modulus E of 162 GPa) and a second interface layer (work function Φ of 4.23 eV) are sequentially deposited on a porous carbon substrate using chemical vapor deposition to construct the composite substrate. During the deposition of the first interface layer, the precursors are PH3 and Ar, with a PH3 flow rate of 50 sccm and an Ar flow rate of 150 sccm. The deposition temperature is 550 °C, the pressure is 120 Pa, and the deposition time is 30 min. During the deposition of the second interface layer, the precursors are TiCl4 and Ar. The flow rate of 4 was 10 sccm, the flow rate of Ar was 50 sccm, the deposition temperature was 500℃, the pressure was 120 Pa, and the deposition time was 10 min. The thickness of the first interface layer was 1.6 nm, and the phosphorus content in the first interface layer was 8.2 at%. The thickness of the second interface layer was 2.3 nm, the contact resistance was 9 Ω·cm², the thickness of the interface layer was 3.9 nm, and the difference between the contact potential of the first interface layer and the work function of the second interface layer was 0.2. All other conditions were the same, and a silicon-carbon composite anode material was obtained, wherein the mass fraction of nano-silicon particles in the silicon-carbon composite anode material was 50%.

[0127] Example 7

[0128] Compared with Example 1, Example 7 differs only in that a second interface layer and a first interface layer are deposited sequentially on a porous carbon substrate using chemical vapor deposition to construct an interface layer, thereby obtaining a composite substrate; all other conditions are the same, resulting in a silicon-carbon composite anode material.

[0129] Example 8

[0130] Compared with Example 1, Example 8 differs only in that, during the deposition of the second interface layer, the precursors are Al(CH3)3 and Ar, the flow rate of Al(CH3)3 is 30 sccm, the flow rate of Ar is 200 sccm, the deposition temperature is 600℃, the pressure is 200 Pa, and the deposition time is 10 min; the thickness of the first interface layer is 1.5 nm, the thickness of the second interface layer is 1.6 nm, the contact resistance is 13 Ω·cm², and the thickness of the interface layer is 3.1 nm; all other conditions are the same, resulting in a silicon-carbon composite anode material.

[0131] Example 9

[0132] Compared with Example 1, Example 9 differs only in that, during the deposition of the first interface layer, the precursors are BCl3 and H2, the flow rate of BCl3 is 50 sccm, the flow rate of H2 is 50 sccm, the deposition temperature is 500℃, the pressure is 100 Pa, and the deposition time is 20 min; the thickness of the first interface layer is 1.5 nm, the thickness of the second interface layer is 1.2 nm, the contact resistance is 8 Ω·cm², and the thickness of the interface layer is 2.7 nm; all other conditions are the same, resulting in a silicon-carbon composite anode material.

[0133] Example 10

[0134] Example 10 differs from Example 1 only in that the carbon coating layer is deposited on the outer surface of a porous carbon substrate with deposited silicon nanoparticles using chemical vapor deposition. During the deposition process, the precursors are C2H2 and Ar, the flow rate of C2H2 is 10 sccm, the flow rate of Ar is 100 sccm, the deposition temperature is 600℃, and the deposition time is 20 min. All other conditions are the same, resulting in a silicon-carbon composite anode material with a carbon coating layer thickness of 8 nm and an ID / IG ratio of 0.9.

[0135] Example 11

[0136] Example 11 differs from Example 1 only in that a first interface layer (elastic modulus E of 400 GPa) and a second interface layer (work function Φ of 4.7 eV) are sequentially deposited on a porous carbon substrate using chemical vapor deposition. During the deposition of the second interface layer, the precursor is cobalt acetylacetonate, the precursor sublimation temperature is 150°C, the flow rate is 30 sccm, Ar and H2 are introduced in a 9:1 ratio, the argon flow rate is 90 sccm, the hydrogen flow rate is 10 sccm, the deposition temperature is 350°C, the pressure is 200 Pa, and the deposition time is 10 min. The thickness of the second interface layer is 1.4 nm, and the contact resistance is 13 Ω·cm². The difference between the contact potential of the first interface layer and the work function of the second interface layer is 0.8. All other conditions are the same, resulting in a silicon-carbon composite anode material.

[0137] Example 12

[0138] Comparative Example 12 differs from Example 1 only in that template agent P123 and phenolic resin (manufacturer: Shengquan, model: 2893B, molecular weight: 800) and 50 mL of anhydrous ethanol are mixed, magnetically stirred for 6 h, transferred to a petri dish, and the solvent is evaporated at 40 °C for 48 h to form an ordered mesoporous structure, thus obtaining pre-prepared porous carbon. The mass ratio of template agent P123 to phenolic resin is 1:20. Then, the pre-prepared porous carbon is heated to 900 °C at 3 °C / min in a nitrogen atmosphere and carbonized for 2 h to obtain a porous carbon substrate. The pore size distribution satisfies the following: micropores account for 10%, mesopores account for 70%, and macropores account for 20%. All other conditions are the same, resulting in a silicon-carbon composite anode material.

[0139] Comparative Example 1

[0140] Comparative Example 1 differs from Example 1 only in that it does not include the step of depositing the first interface layer, that is, directly depositing a second interface layer with a thickness of 2.7 μm on the porous carbon substrate; all other conditions are the same, and a silicon-carbon composite anode material is obtained.

[0141] Comparative Example 2

[0142] Comparative Example 2 differs from Example 1 only in that it does not include the step of depositing a second interface layer, that is, a first interface layer with a thickness of 2.7 μm is directly deposited on a porous carbon substrate; all other conditions are the same, and a silicon-carbon composite anode material is obtained.

[0143] Comparative Example 3

[0144] Comparative Example 3 differs from Example 1 only in that it does not include the step of depositing the first and second interface layers; that is, it directly uses chemical vapor deposition to deposit nano-silicon particles on a porous carbon substrate. All other conditions are the same, and a silicon-carbon composite anode material is obtained.

[0145] Comparative Example 4

[0146] Compared with Example 1, Comparative Example 4 differs only in that the deposition temperature during the deposition of the first interface layer is 750°C and the deposition time is 20 min; the deposition temperature during the deposition of the second interface layer is 700°C and the deposition time is 10 min; the thickness of the first interface layer is 1.6 nm, the thickness of the second interface layer is 1.2 nm, the contact resistance is 8 Ω·cm², and the thickness of the interface layer is 2.8 nm; all other conditions are the same, and a silicon-carbon composite anode material is obtained.

[0147] Comparative Example 5

[0148] Comparative Example 5 differs from Example 1 only in that a first interface layer (elastic modulus E of 100 GPa) and a second interface layer (work function Φ of 4.3 eV) are sequentially deposited on a porous carbon substrate using chemical vapor deposition to construct the interface layer. During the deposition of the first interface layer, the precursors are H2S and Ar, the flow rate of H2S is 40 sccm, the flow rate of Ar is 150 sccm, the deposition temperature is 500℃, the pressure is 100 Pa, and the deposition time is 15 min; all other conditions are the same, resulting in a silicon-carbon composite anode material.

[0149] The silicon carbide content and interfacial impedance of the interface layer in the silicon-carbon composite anode materials prepared in Examples 1-12 and Comparative Examples 1-5 were tested respectively. The test results are shown in Table 1. The specific test methods are as follows:

[0150] Silicon carbide content: The silicon carbide content was tested using XPS depth analysis, with Al Kα rays (1486.6 eV) and a sputtering rate of 0.1 nm / s.

[0151] Interface impedance: A Solartron 1260A electrochemical workstation was used, with the following test conditions: EIS test frequency range 100kHz~10mHz, amplitude 10mV; and then the fitting software ZView was used.

[0152] Meanwhile, silicon-carbon composite anode materials prepared in Examples 1-12 and Comparative Examples 1-5 were used as anode active materials to prepare anode sheets. CR2032 coin cells were prepared using conventional methods for the anode sheets, and the electrical performance of the cells was tested. The specific test methods are as follows:

[0153] Half-cell assembly: Assemble CR2032 coin cells in a glove box, using lithium metal sheets as the counter electrode, polypropylene microporous membranes as the separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), with a LiPF6 concentration of 1 mol / L.

[0154] The assembled button cells were tested using a LAND battery testing system. The charge / discharge voltage range was 0.01V-1.5V, and the temperature was 25±1℃. The test results are shown in Table 1. The specific test methods are as follows:

[0155] 0.1C initial charge / discharge efficiency test steps: 0.1C discharge specific capacity / 0.1C charge specific capacity.

[0156] The 0.1C charge / discharge specific capacity test steps are as follows: 1. Let stand for 5 hours; 2. Discharge at 0.05C to 0.005V; 3. Discharge at 0.05mA constant current to 0.005V; 4. Let stand for 5 minutes; 5. Discharge at 0.01mA constant current to 0.005V; 6. Let stand for 5 minutes; 7. Charge at 0.1C to 2V; 8. Let stand for 5 minutes.

[0157] 0.1C 500-cycle capacity retention rate test procedure: Same as the 0.1C discharge specific capacity test procedure, set the program to loop 500 times and then cut off, and compare its capacity retention rate.

[0158] Data processing: Select 4 data points with a range within 3mAh, remove the maximum and minimum values, and calculate the average.

[0159] Table 1

[0160]

[0161] As shown in Table 1, compared to Examples 1-6, in Examples 4 and 6, the elastic modulus E of the first interface layer and the work function of the second interface layer Φ satisfy the following relationship: when 150 GPa ≤ E < 200 GPa, Φ = 4.3 + 0.003 (E - 150); while in Examples 1 and 6, the elastic modulus E of the first interface layer and the work function of the second interface layer Φ satisfy the following relationship: when E ≥ 200 GPa, 4.6 eV ≤ Φ ≤ 4.9 eV; in Examples 2-3 and 5, the elastic modulus E of the first interface layer and the work function of the second interface layer Φ do not satisfy any of the above relationships, resulting in relatively poor cycle stability and rate performance of the silicon-carbon composite anode material; compared to Examples 1 and 5, chemical vapor deposition can achieve efficient deposition of nano-silicon particles, increasing their loading, which is beneficial to improving the cycle stability and rate performance of the silicon-carbon composite anode material; compared to Examples 1 and 7, controlling the deposition order of the first and second interface layers... This approach is beneficial for improving the cycle stability and rate performance of silicon-carbon composite anode materials. Compared to Examples 1 and 8-9, controlling the deposition temperature of the first and second interface layers within a suitable range during the deposition process helps reduce the silicon carbide content in the anode material, further improving the cycle stability and rate performance of the silicon-carbon composite anode material. Compared to Examples 1 and 10, controlling the ID / IG ratio of the carbon coating layer within a suitable range helps improve the cycle stability and rate performance of the silicon-carbon composite anode material. Compared to Examples 1 and 11, controlling the difference between the contact potential of the first interface layer and the work function of the second interface layer within a suitable range helps improve the cycle stability and rate performance of the silicon-carbon composite anode material. Compared to Examples 1 and 12, controlling the proportion of mesoporous structures in the porous carbon substrate within a suitable range facilitates the uniform deposition of the first and second interface layers and the efficient loading of nano-silicon particles, thus improving the cycle stability and rate performance of the silicon-carbon composite anode material.

[0162] Compared with Example 1 and Comparative Examples 1-3, it can be seen that the interface layer composed of the first interface layer and the second interface layer can not only effectively suppress the reaction between the nano-silicon particles and the porous carbon substrate to form silicon carbide during the deposition process, but also effectively regulate the volume expansion of silicon during the charging and discharging process, thereby improving the cycle stability and rate performance of the silicon-carbon composite anode material. Compared with Example 1 and Comparative Examples 4-5, it can be seen that controlling the deposition temperature of the first interface layer and the second interface layer deposition process, i.e., using a low-temperature chemical vapor deposition process, is beneficial to better suppress the formation of silicon carbide and improve the cycle stability and rate performance of the silicon-carbon composite anode material.

[0163] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material includes a composite substrate and nano-silicon particles loaded on the composite substrate. The composite substrate includes a porous carbon substrate and an interface layer stacked on the porous carbon substrate. The interface layer includes a first interface layer and a second interface layer stacked on top of each other. The first interface layer and the second interface layer are connected by at least chemical bonds. The first interface layer does not contain carbon or silicon and includes at least one of boron, nitrogen, phosphorus, or sulfur. The second interface layer includes at least one of tungsten, molybdenum, tantalum, titanium, nickel, aluminum, zinc, manganese, tin, germanium, silver, gallium, and magnesium. The elastic modulus of the first interface layer is E, where E ≥ 150 GPa. The work function of the second interface layer is Φ, where Φ ≤ 4.9 eV. When 150 GPa ≤ E < 200 GPa, Φ = 4.3 + 0.003(E - 150); or when E ≥ 200 GPa, 4.6 eV ≤ Φ ≤ 4.9 eV.

2. The silicon-carbon composite anode material according to claim 1, characterized in that, The interface layer also satisfies at least one of the following conditions: (1) The interface layer comprises a first interface layer and a second interface layer sequentially stacked on the porous carbon substrate; (2) The interface layer is at least partially disposed in the pores of the porous carbon substrate; (3) The thickness of the interface layer is 2nm-4nm; (4) The difference between the contact potential of the first interface layer and the work function of the second interface layer is ≤0.7; (5) The contact resistance of the second interface layer is ≤20Ω·cm²; (6) The thickness of the first interface layer is 1nm-2nm; (7) The thickness of the second interface layer is 1nm-2nm.

3. The silicon-carbon composite anode material according to claim 1, characterized in that, The porous carbon substrate also satisfies at least one of the following conditions: (1) The pore size distribution of the porous carbon substrate has a mesopore ratio > 80%; (2) The specific surface area of ​​the porous carbon substrate is 200 m² / g-2000 m² / g; (3) The total pore volume of the porous carbon substrate is 0.4 cm³ / g-2.0 cm³ / g; (4) The pore size distribution of the porous carbon substrate satisfies the following conditions: micropores ≤ 10%, mesopores ≥ 85%, and macropores ≤ 5%; (5) The tap density of the porous carbon substrate is 0.05 g / cm³-3 g / cm³; (6) The D of the porous carbon substrate 50 For 100nm-12µm, D 10 70nm-4μm, D 90 It is 150nm-16μm.

4. The silicon-carbon composite anode material according to any one of claims 1-3, characterized in that, The silicon-carbon composite anode material also satisfies at least one of the following conditions: (1) The surface of the silicon-carbon composite anode material is further coated with a carbon coating layer, wherein the thickness of the carbon coating layer is 5nm-20nm; (2) The surface of the silicon-carbon composite anode material is further coated with a carbon coating layer, wherein the ID / IG value of the carbon coating layer is <0.8; (3) The mass fraction of the nano-silicon particles in the silicon-carbon composite anode material is 30%-70%; (4) The silicon carbide content in the silicon-carbon composite anode material is <1 at%; (5) The particle size of the nano-silicon particles is 10nm-50nm.

5. A method for preparing a silicon-carbon composite anode material as described in any one of claims 1-4, characterized in that, Includes the following steps: Provides porous carbon substrates; A first interface layer and a second interface layer are deposited on a porous carbon substrate to construct an interface layer and obtain a composite substrate, wherein the deposition temperature is 400℃-650℃. Silicon nanoparticles are deposited on the composite substrate to obtain a silicon-carbon composite anode material.

6. The method for preparing the silicon-carbon composite anode material according to claim 5, characterized in that, In the step of preparing the composite substrate, at least one of the following conditions must also be met: (1) The temperature for depositing the first interface layer is 550℃-650℃, the pressure is 50Pa-200Pa, and the deposition time is 10min-30min; (2) The temperature for depositing the second interface layer is 400℃-500℃, the pressure is 100Pa-300Pa, and the deposition time is 5min-15min; (3) An interface layer is constructed by sequentially depositing a first interface layer and a second interface layer on a porous carbon substrate using chemical vapor deposition. (4) The pore size distribution of the porous carbon substrate has a mesopore ratio of >80%.

7. The method for preparing the silicon-carbon composite anode material according to claim 5 or 6, characterized in that, The method for preparing the silicon-carbon composite anode material also satisfies at least one of the following conditions: (1) The preparation method of the silicon-carbon composite anode material further includes the following steps: performing carbon coating treatment on the surface of the silicon-carbon composite anode material to form a carbon coating layer, wherein the ID / IG value of the carbon coating layer is <0.8; (2) Nano-silicon particles are deposited on the composite substrate by chemical vapor deposition, wherein the deposition temperature is 350℃-600℃ and the volume ratio of silane gas to hydrogen gas is 1:5-1:

10.

8. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active layer disposed on the surface of the current collector, wherein the composition of the negative electrode active layer includes the silicon-carbon composite negative electrode material as described in any one of claims 1-4.

9. A secondary battery comprising the negative electrode as described in claim 8.

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