Copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material and preparation method thereof

Abstract

The application discloses a copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material and a preparation method thereof. The preparation method comprises the following steps: heating silicon monoxide powder in an inert atmosphere for disintegration, performing acid etching on the disintegrated silicon monoxide to obtain a porous silicon structure; mixing a graphene dispersion liquid and a copper salt precursor solution to prepare a first copper-graphene network structure, adding a solvent to form a first composite buffer slurry containing the first copper-graphene network structure; forming a first copper-graphene buffer layer outside the porous silicon structure through the first composite buffer slurry; performing modification treatment on the first copper-graphene buffer layer, and performing coating treatment of a nitrogen-doped polydopamine carbon protective layer on the modified first copper-graphene buffer layer to obtain the copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material. The method can significantly improve the energy density, improve the cycle performance, enhance the rate performance, prolong the battery life, and realize the effective balance between high silicon loading and cycle performance.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and in particular to a copper / nitrogen co-doped multi-stage silicon-carbon anode material and its preparation method. Background Technology

[0002] With the continuous development of commercial electronic equipment and electric vehicles, the energy storage field has placed more stringent requirements on the performance of lithium-ion batteries. However, the commonly used commercial graphite anodes can no longer meet these requirements, and the development and utilization of anode materials with higher energy density and better cycle performance are urgently needed.

[0003] Silicon materials have extremely low discharge potential and relatively abundant reserves, making them the most promising candidate materials for lithium-ion battery anodes. However, they suffer from severe volume expansion during cycling, leading to bottlenecks such as low initial coulombic efficiency, low cycle capacity retention, short calendar life, and poor rate performance. Currently, the mainstream approach to silicon materials is to reduce the silicon content and combine it with carbon to maintain high capacity. However, this method sacrifices the capacity advantage of silicon-based anode materials, making it difficult to balance high silicon loading with excellent cycle performance, thus restricting the large-scale application of silicon-based anode materials. Summary of the Invention

[0004] In view of this, the present disclosure provides a copper / nitrogen co-doped multi-stage silicon-carbon anode material and its preparation method, which can solve the problems of severe volume expansion, low cycle capacity retention and poor performance in the prior art.

[0005] In a first aspect, embodiments of this disclosure provide a copper / nitrogen co-doped multi-stage silicon-carbon anode material, comprising:

[0006] A micron-scale porous silicon structure; the porous silicon structure is formed by stacking nano-silicon particles, and the porous silicon structure includes a core region, an intermediate region, and an outer region from the inside to the outside, with the pore size of the nanopores in the core region, the intermediate region, and the outer region increasing sequentially;

[0007] A copper-graphene composite buffer layer, comprising a portion covering the porous silicon structure and a portion embedded with nanopores;

[0008] A nitrogen-doped polydopamine carbon protective layer is applied to the outside of the copper-graphene composite buffer layer.

[0009] Optionally, the copper-graphene composite buffer layer includes multiple graphene sheets and copper nanoparticles embedded between adjacent graphene sheets, wherein the extension direction of the graphene sheets is consistent with the extension direction of the porous silicon structure surface on which they are located.

[0010] Optionally, the composite buffer layer includes an inner buffer layer and an outer buffer layer, wherein the copper content of the inner buffer layer is 15wt%-25wt% and the copper content of the outer buffer layer is 65wt%-75wt%.

[0011] Optionally, the nitrogen-doped polydopamine carbon protective layer has a thickness of 20 nm to 30 nm.

[0012] The nitrogen doping content in the nitrogen-doped polydopamine carbon protective layer is 4%-6%;

[0013] The carbon content in the nitrogen-doped polydopamine carbon protective layer is 85%-90%.

[0014] Secondly, this disclosure provides a method for preparing a copper / nitrogen co-doped multi-stage silicon-carbon anode material, which includes:

[0015] Silicon suboxide powder is heated and disproportionated in an inert atmosphere, and the disproportionated silicon suboxide is then acidically etched to obtain a porous silicon structure.

[0016] A graphene dispersion and a copper salt precursor solution were mixed to prepare a first copper-graphene network structure, and a solvent was added to form a first composite buffer slurry containing the first copper-graphene network structure.

[0017] A first copper-graphene buffer layer is formed on the outside of the porous silicon structure using a first composite buffer slurry.

[0018] The first copper-graphene buffer layer is modified, and the modified first copper-graphene buffer layer is coated with a nitrogen-doped polydopamine carbon protective layer to obtain a copper / nitrogen co-doped multi-stage silicon-carbon anode material.

[0019] Optionally, before mixing the graphene dispersion and the copper salt precursor solution to prepare the first copper-graphene network structure, and adding a solvent to form the first composite buffer slurry containing the first copper-graphene network structure, the method further includes:

[0020] A graphene dispersion and a copper salt precursor solution are mixed to prepare a second copper-graphene network structure. A solvent is added to form a second composite buffer slurry containing the second copper-graphene network structure. The copper content in the second composite buffer slurry is less than the copper content in the first composite buffer slurry.

[0021] A second copper-graphene buffer layer is formed outside the porous silicon structure using the second composite buffer slurry.

[0022] The second copper-graphene buffer layer and the first copper-graphene buffer layer together form a copper-graphene composite buffer layer.

[0023] The thickness of the first copper-graphene buffer layer is 40nm-60nm; the thickness of the second copper-graphene buffer layer is 20nm-30nm.

[0024] Optionally, the step of mixing the graphene dispersion and the copper salt precursor solution to prepare a second copper-graphene network structure, and adding a solvent to form a second composite buffer slurry containing the second copper-graphene network structure, includes:

[0025] The prepared graphene dispersion and copper salt precursor solution were mixed at a ratio of 20:80 to 25:75 and stirred at a constant temperature of 60℃-70℃ for 3.5h-4.5h to obtain the first mixed solution. Sodium hydroxide solution was added dropwise to the first mixed solution to adjust the pH to 10-11. After centrifugation and washing, the first solid product was obtained. The first solid product was placed in ethanol to obtain the second composite buffer slurry.

[0026] The copper nanoparticles contained in the first solid product have a particle size of 25nm-30nm.

[0027] Optionally, the step of mixing the graphene dispersion and the copper salt precursor solution to prepare a first copper-graphene network structure, and adding a solvent to form a first composite buffer slurry containing the first copper-graphene network structure, includes:

[0028] The prepared graphene dispersion and copper salt precursor solution were mixed at a ratio of 70:30-80:20 and stirred at a constant temperature of 75℃-80℃ under a nitrogen atmosphere for 5.5h-6.5h to obtain a second mixed solution. The second mixed solution was centrifuged and washed sequentially to obtain a second solid product. The second solid product was then placed in ethanol to obtain the first composite buffer slurry.

[0029] The copper nanoparticles contained in the second solid product have a particle size of 45nm-50nm.

[0030] Optionally, the modified first copper-graphene buffer layer is coated with a nitrogen-doped polydopamine carbon protective layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material, comprising:

[0031] The modified first copper-graphene composite buffer layer was sequentially heated, vacuum dried, and cleaned to obtain the first material.

[0032] The first material is subjected to in-situ dopamine self-polymerization treatment to obtain a second material, the second material having a dense and uniform polydopamine protective layer on its outer side;

[0033] The second material is placed in a nitrogen atmosphere and heat-treated using a programmed temperature rise method. Nitrogen atoms in the dopamine molecules are in situ doped into the carbon network to obtain the third material. The third material has several active sites and a coating layer containing nitrogen-containing polydopamine carbon layers.

[0034] The third material is slowly cooled to room temperature to obtain the copper / nitrogen co-doped multi-stage silicon-carbon anode material.

[0035] Thirdly, embodiments of this disclosure provide a lithium-ion battery, including the copper / nitrogen co-doped multi-level silicon-carbon anode material, or including a copper / nitrogen co-doped multi-level silicon-carbon anode material prepared by the method described above, wherein the copper / nitrogen co-doped multi-level silicon-carbon anode material is the anode material of a lithium-ion battery.

[0036] The method for preparing copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application can significantly improve the energy density of lithium-ion batteries by using a porous silicon structure. The porous silicon structure is formed by stacking nano-silicon particles, which have a high specific surface area and can store more lithium ions, thereby increasing the battery's energy density and effectively alleviating the volume expansion problem of silicon materials during cycling. The pore size of the nano-silicon particles in the porous silicon structure increases from the inside to the outside. This structure not only facilitates the storage and release of lithium ions but also effectively disperses and absorbs volume changes during charging and discharging, thus optimizing the structural stability of the material. The introduction of a copper-graphene composite buffer layer effectively absorbs and disperses the stress generated in silicon materials during charging and discharging, thereby improving cycle performance and capacity retention. The copper-graphene composite buffer layer not only helps alleviate volume expansion but also improves the material's conductivity. The combination of copper nanoparticles and graphene sheets forms a highly efficient conductive network, enabling lithium ions to transport more quickly within the material, thus improving the battery's rate performance. Further coating the copper-graphene composite buffer layer with a nitrogen-doped polydopamine carbon protective layer effectively protects the silicon material from external environmental corrosion and oxidation, extending the battery's lifespan. This method, through rational material design and composite process, successfully balances the relationship between high silicon loading and excellent cycle performance. The combination of porous silicon structure and the copper-graphene composite buffer layer retains the capacity advantages of silicon materials while significantly improving their cycle performance, making large-scale application of silicon-based anode materials possible.

[0037] The above description is merely an overview of the technical solution disclosed herein. In order to better understand the technical means of this disclosure and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this disclosure more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic flowchart illustrating the preparation method of copper / nitrogen co-doped multi-stage silicon-carbon anode material provided in the embodiments of this disclosure.

[0040] Figure 2 This is a schematic flowchart of a method for heating and disproportionating silicon suboxide powder in an inert atmosphere, as provided in an embodiment of this disclosure.

[0041] Figure 3 This is a schematic diagram of a method for modifying a first copper-graphene composite buffer layer according to an embodiment of this disclosure.

[0042] Figure 4 This is a schematic diagram of a method for obtaining a copper / nitrogen co-doped multi-stage silicon-carbon anode material by coating a modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer, as provided in an embodiment of this disclosure.

[0043] Figure 5 for Figure 4 A flowchart illustrating the method for obtaining the second material.

[0044] Figure 6 This is a three-dimensional schematic diagram of a copper / nitrogen co-doped multi-stage silicon-carbon anode material provided in an embodiment of this disclosure.

[0045] Figure 7 for Figure 6 A cross-sectional diagram.

[0046] Figure 8 for Figure 6 A cross-sectional schematic diagram of a porous silicon structure.

[0047] Figure 9 for Figure 6 A schematic diagram of the structure of the copper-graphene composite buffer layer.

[0048] Figure 10 A scanning electron microscope image of silicon suboxide powder provided in an embodiment of this disclosure.

[0049] Figure 11 This is a schematic diagram comparing the XRD patterns of etched silicon suboxide powder with those of original silicon suboxide and silicon suboxide after disproportionation treatment, as provided in an embodiment of this disclosure.

[0050] Figure 12Transmission electron microscopy (TEM) image of particles after the modified first copper-graphene composite buffer layer is coated with a nitrogen-containing polydopamine carbon layer, as provided in the embodiments of this disclosure.

[0051] Figure 13 The spectrum of the composite material with a first copper-graphene composite buffer layer formed after modification treatment, provided in the embodiments of this disclosure, is obtained by Raman testing.

[0052] Figure 14 The XPS spectrum of the material after the modified first copper-graphene composite buffer layer is coated with a nitrogen-containing polydopamine carbon layer according to an embodiment of this disclosure.

[0053] Figure 15 A schematic diagram illustrating the cycling performance of the composite material in a half-cell according to an embodiment of this disclosure.

[0054] Explanation of reference numerals in the attached figures:

[0055] 10. Porous silicon structure; 11. Core region; 12. Intermediate region; 13. Peripheral region; 20. Copper-graphene composite buffer layer; 21. First copper-graphene composite buffer layer; 22. Second copper-graphene composite buffer layer; 30. Nitrogen-doped polydopamine carbon protective layer. Detailed Implementation

[0056] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0057] It should be understood that the following specific examples illustrate the implementation of this disclosure, and those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0058] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0059] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this disclosure. The drawings only show the components related to this disclosure and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0060] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0061] Reference Figure 1 The first aspect of this application discloses a method for preparing a copper / nitrogen co-doped multi-stage silicon-carbon anode material, comprising the following steps:

[0062] S100 involves heating and disproportionating silicon suboxide powder in an inert atmosphere, followed by acid etching of the disproportionated silicon suboxide to obtain a porous silicon structure.

[0063] The porous silicon structure is formed by stacking several nano-sized silicon particles, and the pore size of the nanopores formed by these nano-sized silicon particles increases from the inside to the outside, forming a core region, a middle region, and a peripheral region. The overall porous silicon structure is at the micrometer level.

[0064] The process of heating and disproportionating silicon suboxide powder in an inert atmosphere may include: heating silicon suboxide powder in an inert atmosphere at 800°C-1200°C for 4 to 8 hours; the particle size of the silicon suboxide powder is 500 nm-15 μm.

[0065] Specifically, refer to Figure 2 The method of "heating and disproportionating silicon suboxide powder in an inert atmosphere" in S100 specifically includes:

[0066] S111, silicon suboxide powder is heated to 500℃-550℃ in an inert atmosphere at a rate of 5℃ / min-7℃ / min and held for 1-1.5 hours to obtain silicon suboxide with surface adsorbates removed.

[0067] S112, then raise the temperature to 900℃-950℃ at a rate of 3℃ / min-43℃ / min, and hold for 2-2.5 hours to allow silicon suboxide to begin disproportionation;

[0068] S113 was eventually heated to 1100℃-1150℃ at a rate of 2℃ / min-2.5℃ / min and held for 4-4.5 hours.

[0069] In this embodiment, a programmed temperature rise method is used for heating. Temperature control at A100 removes surface adsorbates from the initial silicon suboxide powder. Temperature control at A200 initiates disproportionation of the silicon suboxide after surface adsorbate removal. Temperature control at A300 completes deep disproportionation. This stepwise temperature control promotes the gradual transformation of silicon suboxide into a mixture of silicon and silicon dioxide, forming a preliminary layered structure at the microscale. This layered structure can effectively form a surface protective layer, releasing stress during the repeated expansion of electrode particles, reducing the probability of electrode material pulverization, and significantly improving particle cycling performance.

[0070] The microstructure of the disproportionation products directly determines the pore size distribution of the final porous silicon. In the temperature range of 900-1000℃, smaller silicon grains (20-30 nm) are mainly formed, constituting the core region of the porous silicon. In the 1000-1050℃ range, medium-sized silicon grains (30-50 nm) are formed, corresponding to the middle region. In the high-temperature range of 1050-1100℃, larger silicon grains (50-80 nm) are formed, ultimately forming the outer region. By precisely controlling the holding time in each temperature range, the proportion of silicon grains in different regions can be adjusted.

[0071] The method of "acid etching of disproportionated silicon suboxide to obtain a porous silicon structure" in S100 includes: immersing the disproportionated silicon suboxide in a mixed acid solution and etching at a preset temperature to obtain a porous silicon structure.

[0072] The mixed acid solution is preferably a mixture of hydrochloric acid solution and hydrofluoric acid solution, with the ratio of hydrochloric acid solution to hydrofluoric acid solution being 1:5 to 1:2.

[0073] The preferred pore size of the obtained porous silicon structure is 1nm-20nm.

[0074] Acid etching is a key step in forming the final porous structure. For "acid etching of disproportionated silicon suboxide to obtain a porous silicon structure" in S100, it includes: placing the disproportionated silicon suboxide in a mixed acid solution and stirring, reacting for 12h-36h in an etching temperature range of -70°C to 25°C, and obtaining porous silicon structure after vacuum filtration.

[0075] Specifically, the disproportionated products can be immersed in a mixed solution of hydrochloric acid and hydrofluoric acid at a volume ratio of 1:3, and etched at -20°C. Firstly, the low temperature effectively reduces the volatilization of hydrofluoric acid, ensuring a suitable etching solution concentration. Secondly, the low temperature helps control the etching rate to decrease evenly, ensuring the formation of a uniform channel structure. The etching process can be divided into three stages: the first 4 hours primarily remove the silica naturally oxidized in the peripheral region, forming large channels of 15nm-20nm; the next 8 hours etch the central region, forming medium-sized channels of 8nm-12nm; and the final 12 hours slowly etch the core region, forming a microporous structure of 3nm-5nm. Magnetic stirring at 400rpm is used throughout the process to ensure etching uniformity.

[0076] Furthermore, after etching, the material can be cleaned sequentially with deionized water, ethanol, and acetone, three times with each solvent, to thoroughly remove residual acid and byproducts. Finally, it is preferably dried under vacuum at 60°C for 12 hours to obtain a porous silicon core material with a gradient pore size distribution. This hierarchical pore structure not only provides a good loading interface for the subsequent copper-graphene composite buffer layer but also provides an ideal spatial structure for the rapid transport of lithium ions and the volume expansion of the silicon material.

[0077] In this embodiment, the porous silicon structure obtained by S100 is divided into three regions from the inside out: 1) Core region (diameter 2μm-3μm): includes densely arranged nano-silicon particles (particle size 20nm-30nm), the pore size of the nanopores formed by the nano-silicon particles in this region is preferably 3nm-5nm, and the porosity is 15%-20%; 2) Middle region (thickness 1.5μm-2μm): includes loosely arranged nano-silicon particles (particle size 30nm-50nm), the pore size of the nanopores formed by the nano-silicon particles in this region is preferably 8nm-12nm, and the porosity is 25%-30%; 3) Peripheral region (thickness 1μm-1.5μm): includes interconnected nano-silicon particles (particle size 50nm-80nm), the pore size of the nanopores formed by the nano-silicon particles in this region is preferably 15nm-20nm, and the porosity is 35%-40%.

[0078] The pore structure is a dendritic hierarchical pore system that gradually coarsens from the inside out. This hierarchical pore system, which gradually coarsens from the inside out, can gradually alleviate the particle deformation caused by the volume expansion of the particles during the circulation process, realize the gradient release of stress, and thus create an effect of gradually increasing mechanical strength from the inside out.

[0079] For example, the porous silicon structure obtained by S100 can be a porous silicon particle with a core region pore size of 4 nm, a middle region pore size of 10 nm, and a peripheral region pore size of 18 nm. This gradient pore size distribution not only ensures the mechanical strength of the material, but also lays a good foundation for subsequent electrochemical performance optimization.

[0080] S200: A graphene dispersion and a copper salt precursor solution are mixed to prepare a first copper-graphene network structure. A solvent is then added to form a first composite buffer slurry containing the first copper-graphene network structure.

[0081] Specifically, 1) the prepared graphene dispersion and copper salt precursor solution are mixed at a ratio of 70:30-80:20 to obtain a high copper content; 2) after constant temperature stirring at 75℃-80℃ under a nitrogen atmosphere for 5.5h-6.5h, a second mixed solution is obtained so that the copper nanoparticles can grow to the preset particle size; wherein, the process is carried out under a nitrogen atmosphere to prevent the copper nanoparticles from being oxidized, and at the same time, it is beneficial to form a more complete conductive network structure; 3) after the second mixed solution is centrifuged and washed in sequence, a second solid product is obtained, and the second solid product is placed in ethanol to obtain a first composite buffer slurry.

[0082] The second solid product contains copper nanoparticles with a particle size of 45nm-50nm.

[0083] S300 forms a first copper-graphene buffer layer on the outside of a porous silicon structure using a first composite buffer slurry.

[0084] Specifically, the porous silicon structure is placed in a first composite buffer slurry, ultrasonically treated, then vacuum filtered, dried, and heat-treated to obtain a porous silicon structure and a first copper-graphene buffer layer formed on the outside of the porous silicon structure.

[0085] Furthermore, this application also includes: before mixing the graphene dispersion and the copper salt precursor solution to prepare the first copper-graphene network structure, and adding a solvent to form a first composite buffer slurry containing the first copper-graphene network structure, the application further includes:

[0086] 1) A graphene dispersion and a copper salt precursor solution are mixed to prepare a second copper-graphene network structure. A solvent is added to form a second composite buffer slurry containing the second copper-graphene network structure. The copper content in the second composite buffer slurry is less than the copper content in the first composite buffer slurry.

[0087] 2) A second copper-graphene buffer layer is formed on the outside of the porous silicon structure by means of a second composite buffer slurry; the second copper-graphene buffer layer and the first copper-graphene buffer layer constitute a copper-graphene composite buffer layer.

[0088] In this embodiment, the thickness of the first copper-graphene buffer layer is 40nm-60nm; the thickness of the second copper-graphene buffer layer is 20nm-30nm.

[0089] The copper-graphene composite buffer layer includes a copper-graphene network structure, which comprises graphene sheets oriented parallel to the surface of silicon particles, with copper nanoparticles embedded in the gaps between the graphene sheets.

[0090] The second copper-graphene buffer layer is an inner buffer layer, mainly used to make full contact with the surface of silicon particles in the porous silicon structure, so as to form a good interface bond with the porous silicon structure; the first copper-graphene buffer layer is an outer buffer layer, mainly used to provide an efficient electron transport channel.

[0091] In this embodiment, the method for preparing the graphene dispersion includes: dispersing graphene oxide in deionized water at a concentration of 0.5 mg / mL, and ultrasonically treating it for 2 hours to form a stable dispersion, which is the desired graphene dispersion.

[0092] The method for preparing a copper salt precursor solution includes: dissolving copper sulfate and ascorbic acid (mass ratio 1:2) in ethylene glycol to prepare the desired copper salt precursor solution.

[0093] Specifically, a graphene dispersion and a copper salt precursor solution are mixed to prepare a second copper-graphene network structure. A solvent is added to form a second composite buffer slurry containing the second copper-graphene network structure, comprising:

[0094] The prepared graphene dispersion and copper salt precursor solution were mixed at a ratio of 20:80 to 25:75 and stirred at a constant temperature of 60℃-70℃ for 3.5h-4.5h to obtain the first mixed solution. Sodium hydroxide solution was added dropwise to the first mixed solution to adjust the pH to 10-11. After centrifugation and washing, the first solid product was obtained. The first solid product was then placed in ethanol to obtain the second composite buffer slurry.

[0095] The copper nanoparticles contained in the first solid product have a particle size of 25nm-30nm.

[0096] During the constant-temperature stirring process, ascorbic acid reduces copper ions while also partially reducing graphene oxide.

[0097] Furthermore, in the second composite buffer slurry, the average particle size of the copper nanoparticles is approximately 30 nm.

[0098] In this embodiment, the porous silicon structure is first immersed in the prepared second composite buffer slurry, and then ultrasonically treated for 30 minutes to allow the slurry to fully penetrate the pore structure and fully contact the surface of the silicon particles. After that, it is filtered under reduced pressure to form a uniform second copper-graphene buffer layer. After drying at 110℃-130℃ (preferably 120℃) for 2-3 hours (preferably 2 hours), the inner composite material is obtained. The inner composite material includes the porous silicon structure and the second copper-graphene buffer layer covering the porous silicon structure.

[0099] Ultrasonic treatment helps improve the permeability and uniformity of the slurry within the porous silicon structure. During vacuum filtration, the second composite buffer slurry is uniformly coated onto the silicon particles in the porous silicon structure, forming a coating layer. In this inner composite material, the inner slurry forms a good interfacial bond with the porous silicon structure.

[0100] Then, the inner composite material is immersed in the first composite buffer slurry, ultrasonically treated for 30 minutes, and then vacuum filtered to form a uniform first copper-graphene buffer layer. After drying at 60℃-80℃ (preferably 80℃) for 2-3 hours (preferably 2 hours), the target sample is obtained. The target sample includes a porous silicon structure, a second copper-graphene buffer layer covering the porous silicon structure, and a first copper-graphene buffer layer covering the outside of the second copper-graphene buffer layer. That is, the target sample can be understood as including a porous silicon structure and a copper-graphene composite buffer layer covering the porous silicon structure.

[0101] The final heat treatment process is crucial for optimizing the interface structure: specifically, in a hydrogen / argon (5:95) mixed atmosphere, the temperature is increased to 300°C at a rate of 2°C / min and held for 2 hours. This step promotes the formation of a stable interface bond between copper nanoparticles and graphene. The cooling process adopts natural cooling to reduce the generation of thermal stress.

[0102] In this embodiment, the copper-graphene composite buffer layer includes an inner layer (i.e., the second copper-graphene buffer layer) and an outer layer (i.e., the first copper-graphene buffer layer). The inner layer can be understood as a first deposited layer obtained by placing a porous silicon structure in an inner layer slurry (i.e., the second composite buffer slurry), and the outer layer can be understood as a new deposited layer, i.e., the second deposited layer, obtained by immersing the inner layer composite material in an outer layer slurry (i.e., the first composite buffer slurry). In this embodiment, the first deposited layer ensures good interfacial bonding with the porous silicon structure, and the second deposited layer provides an efficient electron transport channel.

[0103] Through the S100-S300 process, a copper-graphene composite buffer layer with stable structure and excellent conductivity can be obtained.

[0104] Experiments show that when the inner layer thickness is 25 nm and the outer layer thickness is 50 nm, the composite material exhibits the best overall performance. This pore size-thickness gradient structure design not only solves the problem of insufficient conductivity of traditional carbon coating layers, but also provides excellent mechanical buffering effect.

[0105] S400, the first copper-graphene buffer layer is modified, and the modified first copper-graphene buffer layer is coated with a nitrogen-doped polydopamine carbon protective layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material.

[0106] Specifically, the copper / nitrogen co-doped multi-level silicon-carbon anode material comprises, from the center to the outside: a porous silicon structure at the core, a first copper-graphene composite buffer layer covering the nano-silicon particles in the porous silicon structure, and a nitrogen-doped polydopamine carbon protective layer, wherein the copper nanoparticles are partially embedded in the peripheral pores of the porous silicon structure.

[0107] In this embodiment, surface modification and protective layer preparation are key steps to ensure the long-term stability of the composite material. The core of these steps lies in constructing a chemically bonded interface structure and a functionalized protective layer.

[0108] Specific reference Figure 3 The method for "modifying the first copper-graphene buffer layer" in S400 specifically includes:

[0109] A100, the coupling agent is determined.

[0110] In this embodiment, 3-aminopropyltriethoxysilane (APTES) is preferably used as the coupling agent.

[0111] A200 involves mixing the coupling agent with ethanol at a mass percentage of 0.5%-0.7% to obtain an ethanol solution of the coupling agent.

[0112] Specifically, the copper-graphene composite buffer layer sample was immersed in a 0.5wt%-0.7wt% APTES ethanol solution to obtain a coupling agent ethanol solution.

[0113] A300 is used to immerse the copper-graphene composite buffer layer in a coupling agent ethanol solution and stir it at 40℃-45℃ for 2-2.5 hours to obtain the modified copper-graphene composite buffer layer.

[0114] This step allows the alkoxy group of the silane coupling agent to undergo a condensation reaction with the hydroxyl group on the material surface, while simultaneously introducing active amino groups onto the surface, providing reaction sites for the subsequent polymerization of dopamine.

[0115] Reference Figure 4The method in S400, which involves "coating the modified first copper-graphene buffer layer with a nitrogen-doped polydopamine carbon protective layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material," specifically includes:

[0116] B100, the modified first copper-graphene composite buffer layer is sequentially heated, vacuum dried and cleaned to obtain the first material.

[0117] Specifically, the sample was dried in a vacuum environment at 80℃-85℃ for 4-4.5 hours to promote the complete condensation and cross-linking of the silane coupling agent. It was then rinsed three times repeatedly with anhydrous ethanol to remove unreacted APTES molecules. The key to this step is controlling the density of the surface amino groups; excessively high amino group density will lead to excessively rapid subsequent dopamine polymerization, affecting the uniformity of the protective layer.

[0118] B200, the first material is subjected to in-situ dopamine self-polymerization treatment to obtain the second material, the outer side of which has a dense and uniform polydopamine protective layer.

[0119] Specific reference Figure 5 The "method for obtaining the second material" in B200 specifically includes:

[0120] B210, place the first material and dopamine hydrochloride in the prepared Tris buffer to obtain the first solution.

[0121] The Tris buffer solution was prepared with a pH of 8.5 and a concentration of 0.01 mol / L.

[0122] Specifically, the first material is dispersed in Tris buffer, and dopamine hydrochloride is dissolved in the buffer at a concentration of 2 mg / mL to obtain the first solution.

[0123] B220, the first solution is ultrasonically treated, and 10 mL of dopamine solution is added dropwise to the treated first solution while stirring with a magnetic stirrer for 24 hours to obtain the second material.

[0124] Specifically, to ensure uniform dispersion, the mixture was ultrasonically treated for 15 minutes; then, dopamine solution was slowly added dropwise at room temperature, with the stirring speed maintained at 400 rpm throughout the process; the polymerization reaction lasted for 24 hours.

[0125] Kinetic control of the polymerization process is extremely important. The first 4 hours are the nucleation stage, during which dopamine preferentially polymerizes at the amino sites on the surface; the next 8 hours are the growth stage, during which polydopamine gradually forms a complete protective layer; the final 12 hours are the crosslinking stage, during which more chemical crosslinks form between polymer chains, improving the mechanical strength of the protective layer. Throughout the process, the polymerization rate is adjusted by controlling the temperature (25±2℃) and pH (8.5±0.1) to ensure the formation of a dense and uniform protective layer.

[0126] After the protective layer is formed, nitrogen doping is required to improve conductivity, so B300 is then performed.

[0127] B300, the second material is placed in a nitrogen atmosphere and heat-treated by a programmed temperature rise method. Nitrogen atoms in the dopamine molecule are in situ doped into the carbon network to obtain the third material. The third material has several active sites and a coating layer containing nitrogen-containing polydopamine carbon layer.

[0128] Specifically, the temperature is first raised to 200℃-220℃ at a rate of 5℃ / min-6℃ / min and held for 1-1.2 hours to remove residual moisture; then the temperature is raised to 400℃-420℃ at a rate of 3℃ / min-3.5℃ / min and held for 2-2.5 hours. During this stage, polydopamine is converted into a nitrogen-containing carbon layer.

[0129] During the heat treatment process, nitrogen atoms in dopamine molecules are in situ doped into the carbon network, forming active sites such as pyridine nitrogen and pyrrole nitrogen.

[0130] B400 was used to slowly cool the third material to room temperature to obtain a copper / nitrogen co-doped multi-stage silicon-carbon anode material.

[0131] In this embodiment, the final cooling process also requires precise control. Specifically, a slow cooling rate of 2℃ / min-2.5℃ / min can be used to reduce thermal stress and prevent cracking of the protective layer. After cooling to room temperature, the protective layer in the resulting copper / nitrogen co-doped multi-stage silicon-carbon anode material has the following characteristics: uniform thickness (25±2nm), moderate nitrogen doping (5±0.5at%), low surface roughness (Ra<5nm), and strong adhesion to the substrate.

[0132] Through this multi-step surface modification and protective layer preparation process, a functionalized carbon layer with high conductivity and excellent mechanical properties is formed on the surface of the composite material. This protective layer not only effectively prevents excessive electrolyte penetration but also provides additional lithium storage sites through its unique nitrogen-doped structure, thereby improving the overall electrochemical performance of the material. Experiments have shown that this design enables the material to maintain stable structural integrity during more than 100 cycles, which is an important guarantee for realizing high-performance lithium-ion battery anode materials.

[0133] The method for preparing copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application combines the synergistic reinforcement structure of copper-graphene with a gradient porous design, which not only solves the intrinsic problems of silicon materials, but also gives full play to the advantages of each component, forming a novel composite material system that is logically complete and technically feasible.

[0134] The method for preparing copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application can significantly improve the energy density of lithium-ion batteries by using a porous silicon structure. The porous silicon structure is formed by stacking nano-silicon particles, which have a high specific surface area and can store more lithium ions, thereby increasing the battery's energy density and effectively alleviating the volume expansion problem of silicon materials during cycling. The pore size of the nano-silicon particles in the porous silicon structure increases from the inside to the outside. This structure not only facilitates the storage and release of lithium ions but also effectively disperses and absorbs volume changes during charging and discharging, thus optimizing the structural stability of the material. The introduction of a copper-graphene composite buffer layer effectively absorbs and disperses the stress generated in silicon materials during charging and discharging, thereby improving cycle performance and capacity retention. The copper-graphene composite buffer layer not only helps alleviate volume expansion but also improves the material's conductivity. The combination of copper nanoparticles and graphene sheets forms a highly efficient conductive network, enabling lithium ions to transport more quickly within the material, thus improving the battery's rate performance. Further coating the copper-graphene composite buffer layer with a nitrogen-doped polydopamine carbon protective layer effectively protects the silicon material from external environmental corrosion and oxidation, extending the battery's lifespan. This method, through rational material design and composite process, successfully balances the relationship between high silicon loading and excellent cycle performance. The combination of porous silicon structure and the copper-graphene composite buffer layer retains the capacity advantages of silicon materials while significantly improving their cycle performance, making large-scale application of silicon-based anode materials possible.

[0135] In summary, the copper / nitrogen co-doped multi-level silicon-carbon anode material preparation method disclosed in this application has significant advantages in improving the energy density, cycle performance, rate performance and calendar life of lithium-ion batteries, and provides an effective solution to the bottleneck problems of existing silicon-based anode materials in application.

[0136] Specifically, the method for preparing copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application involves heating and disproportionating silicon suboxide powder in an inert atmosphere followed by acid etching. The resulting porous silicon structure is formed by stacking nano-silicon particles, with the pore size increasing from the inside out. This structural design not only increases the specific surface area of ​​the material but also helps improve its mechanical strength and electrical conductivity. By embedding copper nanoparticles into the interlayer gaps of graphene sheets to form a copper-graphene network structure, this composite buffer layer effectively improves the material's electrical and thermal conductivity while enhancing its mechanical stability. Furthermore, the coating treatment with a nitrogen-doped polydopamine carbon protective layer further improves the material's chemical stability and mechanical durability, while also imparting certain functional properties, such as improved oxidation resistance. The material exhibits excellent chemical and corrosion resistance; different treatments and material selections for the inner and outer layers allow the composite material to exhibit different performance characteristics in various application scenarios, enhancing its application range through design flexibility; from material selection and processing to final heat treatment and protective coating, every step of the process is precisely controlled to ensure the stable performance and quality of the final product; operation under inert and nitrogen atmospheres reduces environmental pollution and aligns with the trend of green manufacturing; due to its excellent conductivity and structural stability, this copper / nitrogen co-doped multi-stage silicon-carbon anode material has broad application prospects in energy storage devices such as lithium-ion batteries and supercapacitors; in the field of composite materials, its high specific surface area and excellent mechanical properties allow it to enhance the performance of other materials.

[0137] Reference Figure 6 and Figure 7 Secondly, the copper / nitrogen co-doped multi-level silicon-carbon anode material prepared according to the preparation method of the copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in the first aspect specifically includes a porous silicon structure 10, a copper-graphene composite buffer layer 20 covering the outside of the porous silicon structure, and a nitrogen-doped polydopamine carbon protective layer 30 covering the outside of the copper-graphene composite buffer layer. The total diameter of the porous silicon structure is preferably 5μm-8μm, and the porosity of the porous silicon structure is 15%-20%.

[0138] In this embodiment, taking a copper / nitrogen co-doped multi-level silicon-carbon anode material with an overall outer diameter of 6 μm as an example, preferably, in the porous silicon structure serving as the core layer, the diameter of the core region is 2.5 μm, the pore size of the nanopores in the core region is 4 nm, and the porosity in the core region is 18%; the thickness of the middle region is 1.8 μm, the pore size of the nanopores in the middle region is 10 nm, and the porosity in the middle region is 28%; the thickness of the outer region is 1.2 μm, the pore size of the nanopores in the outer region is 18 nm, and the porosity in the outer region is 38%.

[0139] In the copper-graphene composite buffer layer that serves as the intermediate layer, the inner layer size is preferably 25 nm, the inner layer is mainly composed of graphene, and the copper content in the inner layer is preferably 20 wt%; the outer layer size is preferably 50 nm, and the copper content in the outer layer is preferably 70 wt%.

[0140] A nitrogen-doped polydopamine carbon protective layer is coated on the outside of a copper-graphene composite buffer layer. The thickness of the nitrogen-doped polydopamine carbon protective layer is 20nm-30nm. Its compositional characteristics include a nitrogen doping content of 4%-6% and a carbon content of 85%-90%. Residual functional groups include hydroxyl and amino groups, which are used for interfacial bonding. The structural characteristics of the nitrogen-doped polydopamine carbon protective layer are: density >95%, surface roughness Ra <5nm; and coating integrity: no exposed areas.

[0141] Furthermore, the thickness of the nitrogen-doped polydopamine carbon protective layer as the outer layer is preferably 25 nm, the nitrogen doping amount is preferably 5.2 at%, and the surface roughness is preferably 3.8 nm.

[0142] Specific example: A nitrogen-doped polydopamine carbon protective layer with a thickness of 25 nm and a nitrogen doping amount of 5 at% has an interface structure design including: 1) Core layer / intermediate layer interface: The transition band width of this interface is 10-15 nm, in which copper nanoparticles are partially embedded in the porous silicon peripheral region channels, and this interface forms Si-O-Cu bonds; 2) Intermediate layer / outer layer interface: The transition band width is 5-8 nm, and covalent bonds are formed through amino and hydroxyl groups, with a gradient chemical composition.

[0143] This structural design achieves synergistic optimization of mechanical and electrochemical properties by precisely controlling the parameters and interface characteristics of each layer, providing a new design approach for high-performance silicon-based anode materials.

[0144] Reference Figure 8 The porous silicon structure is formed by stacking several nano-silicon particles, and the pore size of the nanopores formed by these nano-silicon particles increases from the inside to the outside, forming a core region 11, a middle region 12, and a peripheral region 13. The overall porous silicon structure is at the micrometer level.

[0145] In porous silicon structures, porosity increases from the inside out, and the pore size of nanopores increases from the inside out.

[0146] The nanopores in the core region have a pore size of 3nm-5nm, a porosity of 15%-20%, and a diameter of 2μm-3μm; the nanopores in the middle region have a pore size of 8nm-12nm, a porosity of 25%-30%, and a thickness of 1.5μm-2μm; the nanopores in the outer region have a pore size of 15nm-20nm, a porosity of 35%-40%, and a thickness of 1μm-1.5μm.

[0147] Reference Figure 9 The copper-graphene composite buffer layer (i.e., the copper-graphene synergistic reinforced composite buffer layer) includes a copper-graphene network structure, which includes graphene sheets oriented parallel to the surface of silicon particles. Copper nanoparticles are embedded in the gaps between the graphene sheets, that is, the copper nanoparticles are located in the gaps between the graphene sheets, forming a "rivet" structure.

[0148] In this embodiment, the copper-graphene composite buffer layer includes an inner layer and an outer layer. The copper particle size in the inner layer is preferably 30 nm, and the inner layer is mainly composed of graphene sheets with a sheet size of 0.5 μm-1 μm. The copper particle size in the outer layer is preferably 50 nm, and the outer layer is also mainly composed of graphene sheets with a sheet size of 1 μm-2 μm.

[0149] The total thickness of the copper-graphene composite buffer layer is preferably 75 nm, and the continuity of the conductive mesh is preferably greater than 95%.

[0150] It should be noted that, Figures 6 to 9 The diagram provided is for the purpose of facilitating understanding of the structure and does not limit the scope of protection of this application.

[0151] Furthermore, referring to Figure 10 The figure shows a scanning electron microscope (SEM) image of silicon suboxide powder provided in an embodiment of this disclosure. The silicon suboxide particles shown in the figure are used as a precursor material for high-temperature disproportionation. The average diameter of the particles is 10 micrometers, and the edges of the particles are not clear in the SEM image, indicating that the unmodified silicon suboxide material has poor conductivity.

[0152] Reference Figure 11 The figure shows a comparison of the XRD patterns of etched silicon suboxide powder with those of raw silicon suboxide and silicon suboxide after disproportionation treatment, according to an embodiment of this disclosure. In the figure, m-SiO represents the XRD pattern of raw silicon suboxide particles, d-SiO represents the XRD pattern of disproportionated silicon suboxide, and p-Si represents the pattern of etched silicon suboxide. The m-Si XRD pattern shows a peak, indicating that the raw silicon suboxide particles are amorphous and lack obvious crystalline features. After disproportionation treatment, the d-SiO pattern shows that the particles exhibit obvious crystalline features after high-temperature treatment, with sharper peaks and a higher degree of crystallinity. However, a peak still appears in the pattern, indicating that a small amount of amorphous silicon suboxide remains after high-temperature disproportionation, which significantly affects the material's cycle capacity. Following the etching process, the p-Si pattern shows that the amorphous silicon suboxide has been completely removed, while crystalline silicon is well preserved.

[0153] Reference Figure 12The figure shows a transmission electron microscope (TEM) image of particles after the modified first copper-graphene composite buffer layer is coated with a nitrogen-containing polydopamine carbon layer according to an embodiment of this disclosure. The core layer and outer carbon layer structure of the particles in the embodiment can be clearly distinguished in the figure. The carbon layer thickness is adjusted to about 25 nm by reasonable parameter control.

[0154] Reference Figure 13 The image shows the Raman spectrum of the composite material with a first copper-graphene composite buffer layer formed after modification, as provided in this embodiment of the present disclosure. The D / G ratio in the image shows that the D peak is relatively high in the prepared composite material, indicating that there are still many defects in the graphene in the prepared material and the degree of graphitization is low.

[0155] Reference Figure 14 The XPS spectrum of the material after the modified first copper-graphene composite buffer layer is coated with a nitrogen-containing polydopamine carbon layer according to an embodiment of this disclosure is shown. The figure shows the elemental peak distribution including O, N, C and Si, indicating that the nitrogen-containing dopamine is successfully coated on the material surface, forming an effective interface protective layer.

[0156] Reference Figure 15 The figure shows a schematic diagram of the cycling performance of the composite material provided in this embodiment in a half-cell; the initial discharge capacity of this embodiment is 1386.12 mAh g. -1 Furthermore, the discharge capacity increases slightly with the number of cycles, reaching 1496.02 mAh / g after 100 cycles. -1 It maintains 100% charge-discharge efficiency within 100 cycles, demonstrating excellent cycle performance.

[0157] On the other hand, this application discloses a lithium-ion battery, including the copper / nitrogen co-doped multi-level silicon-carbon anode material, or including a copper / nitrogen co-doped multi-level silicon-carbon anode material prepared by the copper / nitrogen co-doped multi-level silicon-carbon anode material preparation method, wherein the copper / nitrogen co-doped multi-level silicon-carbon anode material is the anode material of the lithium-ion battery.

[0158] The basic principles of this disclosure have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this disclosure are merely examples and not limitations, and should not be considered as essential features of each embodiment of this disclosure. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of this disclosure to the necessity of employing the aforementioned specific details for implementation.

[0159] In this disclosure, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The block diagrams of devices, apparatuses, devices, and systems involved in this disclosure are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as "comprising," "including," "having," etc., are open-ended terms meaning "including but not limited to," and are used interchangeably with them. The terms "or" and "and" as used herein refer to the terms "and / or," and are used interchangeably with them unless the context clearly indicates otherwise. The term "such as" as used herein refers to the phrase "such as but not limited to," and is used interchangeably with it.

[0160] Additionally, as used herein, the "or" used in a list of items beginning with "at least one" indicates a separate list, such that a list of, for example, "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not imply that the described example is preferred or better than other examples.

[0161] It should also be noted that in the systems and methods of this disclosure, the components or steps can be decomposed and / or recombined. These decompositions and / or recombinations should be considered as equivalent solutions to this disclosure.

[0162] Various changes, substitutions, and modifications can be made to the technology described herein without departing from the teachings defined by the appended claims. Furthermore, the scope of the claims of this disclosure is not limited to the specific aspects of the processes, machines, manufactures, events, means, methods, and actions described above. Currently existing or later-developed processes, machines, manufactures, events, means, methods, or actions that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein can be utilized. Therefore, the appended claims include such processes, machines, manufactures, events, means, methods, or actions within their scope.

[0163] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0164] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for preparing a copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material, characterized in that, The application relates to a copper / nitrogen co-doped multi-level silicon-carbon negative electrode material and a preparation method thereof. The silicon monoxide powder is heated and disintegrated in an inert atmosphere, and the disintegrated silicon monoxide is subjected to acid etching to obtain a porous silicon structure; The graphene dispersion liquid and the copper salt precursor solution are mixed to prepare a first copper-graphene network structure, and a solvent is added to form a first composite buffer slurry containing the first copper-graphene network structure; A first copper-graphene buffer layer is formed outside the porous silicon structure through the first composite buffer slurry; The first copper-graphene buffer layer is subjected to modification treatment, and the modified first copper-graphene buffer layer is subjected to coating treatment of a nitrogen-doped polydopamine carbon protective layer to obtain the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material; The silicon monoxide powder is heated and disintegrated in an inert atmosphere, and the disintegrated silicon monoxide is subjected to acid etching to obtain a porous silicon structure; The silicon monoxide powder is heated and disintegrated in an inert atmosphere, and the disintegrated silicon monoxide is subjected to acid etching to obtain a porous silicon structure; The silicon monoxide powder is heated and disintegrated in an inert atmosphere, and the disintegrated silicon monoxide is subjected to acid etching to obtain a porous silicon structure; The silicon monoxide powder is heated and disintegrated in an inert atmosphere, and the disintegrated silicon monoxide is subjected to acid etching to obtain a porous silicon structure.

2. The preparation method of the copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material according to claim 1, characterized in that, Before the graphene dispersion liquid and the copper salt precursor solution are mixed to prepare a first copper-graphene network structure, and a solvent is added to form a first composite buffer slurry containing the first copper-graphene network structure, the method further comprises the following steps: The graphene dispersion liquid and the copper salt precursor solution are mixed to prepare a second copper-graphene network structure, and a solvent is added to form a second composite buffer slurry containing the second copper-graphene network structure, wherein the copper content in the second composite buffer slurry is less than that in the first composite buffer slurry; A second copper-graphene buffer layer is formed outside the porous silicon structure through the second composite buffer slurry; The second copper-graphene buffer layer and the first copper-graphene buffer layer constitute a copper-graphene composite buffer layer; The thickness of the first copper-graphene buffer layer is 40nm-60nm; and the thickness of the second copper-graphene buffer layer is 20nm-30nm.

3. The preparation method of the copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material according to claim 2, characterized in that, The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material comprises the following steps: The configured graphene dispersion liquid and the copper salt precursor solution are mixed at a ratio of 20:80-25:75, and a first mixed solution is obtained after constant-temperature stirring at 60-70 DEG C for 3.5-4.5h; sodium hydroxide solution is added dropwise into the first mixed solution to adjust the pH value to 10-11; after centrifugation and washing, a first solid product is obtained, and the first solid product is placed in ethanol to obtain the second composite buffer slurry; The copper nanoparticles contained in the first solid product have a particle size of 25-30nm.

4. The preparation method of the copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material according to claim 3, characterized in that, The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material comprises the following steps: The configured graphene dispersion liquid is mixed with the copper salt precursor solution according to 70:30-80:20, and a second mixed solution is obtained after constant temperature stirring at 75-80°C under a nitrogen atmosphere for 5.5-6.5h. The second mixed solution is subjected to centrifugation and washing in sequence to obtain a second solid product, and the second solid product is placed in ethanol to obtain the first composite buffer slurry. The copper nanoparticles contained in the second solid product have a particle size of 45-50nm.

5. The preparation method of the copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material according to claim 1, characterized in that, The first copper-graphene composite buffer layer after modification treatment is subjected to nitrogen-doped polydopamine carbon protective layer coating treatment to obtain a copper / nitrogen co-doped multi-level silicon-carbon negative electrode material, which comprises: The first material is obtained by sequentially subjecting the first copper-graphene composite buffer layer after modification treatment to heating, vacuum drying and cleaning treatment. The second material is obtained by subjecting the first material to in-situ self-polymerization treatment of dopamine, and the second material has a dense and uniform polydopamine protective layer on the outside. The second material is placed in a nitrogen atmosphere and subjected to heat treatment in a programmed temperature rising manner, so that nitrogen atoms in the dopamine molecules are in-situ doped into the carbon network to obtain a third material. The third material has a plurality of active sites and has a coating layer of nitrogen-containing polydopamine carbon. The third material is slowly cooled and cooled to room temperature to obtain the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material.

6. A copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material, characterized in that, The copper / nitrogen co-doped multi-level silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1-5, and the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material comprises: micron-sized porous silicon structure; the porous silicon structure is formed by stacking nanosilicon particles, and the porous silicon structure comprises an inner core region, an intermediate region and an outer peripheral region from inside to outside, and the pore size of the nanopores in the inner core region, the intermediate region and the outer peripheral region increases in sequence; copper-graphene composite buffer layer, which comprises a portion coated on the outside of the porous silicon structure and a portion embedded in the nanopores; nitrogen-doped polydopamine carbon protective layer, which is coated on the outside of the copper-graphene composite buffer layer. 7.The copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material of claim 6, wherein, The copper-graphene composite buffer layer comprises a plurality of graphene sheet layers and copper nanoparticles embedded between adjacent two graphene sheet layers, and the extension direction of the graphene sheet layer is consistent with the extension direction of the surface of the porous silicon structure in which the graphene sheet layer is located. 8.The copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material of claim 7, wherein, The composite buffer layer comprises an inner buffer layer and an outer buffer layer, and the copper content of the inner buffer layer is 15wt%-25wt%, and the copper content of the outer buffer layer is 65wt%-75wt%. 9.The copper / nitrogen co-doped multi-stage silicon-carbon negative electrode material of claim 6, wherein, The thickness of the nitrogen-doped polydopamine carbon protective layer is 20-30nm; The nitrogen-doped amount in the nitrogen-doped polydopamine carbon protective layer is 4%-6%; The carbon content in the nitrogen-doped polydopamine carbon protective layer is 85%-90%.

10. A lithium-ion battery, characterized by, The copper / nitrogen co-doped multi-level silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1-5, and the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material is a negative electrode material for a lithium ion battery.

Images