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

Abstract

The invention discloses a copper / nitrogen co-doped multistage silicon carbon negative electrode material and a preparation method thereof. The preparation method comprises the following steps: heating and disproportionating silicon monoxide powder in an inert atmosphere, and performing acid etching on disproportionated silicon monoxide to obtain a porous silicon structure; the method comprises the following steps: mixing a graphene dispersion liquid and a copper salt precursor solution to prepare a first copper-graphene network structure, and adding a solvent to form 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; modifying the first copper-graphene buffer layer, and coating the modified first copper-graphene buffer layer with a nitrogen-doped polydopamine carbon protective 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 capability, prolong the service life of the battery, and realize effective balance between high-silicon load and the cycle performance.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion batteries, and particularly to a copper / nitrogen co-doped multi-level silicon-carbon anode material and a preparation method thereof. Background Art

[0002] With the continuous development of commercial electronic devices and the field of electric vehicles, the energy storage field has more stringent requirements for many performance of lithium-ion batteries. However, the currently common commercial graphite anodes can no longer meet the relevant requirements, and the development and utilization of anode materials with higher energy density and more excellent cycle performance are imminent.

[0003] Silicon materials have extremely low discharge potentials and relatively rich reserves, so they have become the most promising alternative materials for the anodes of current lithium-ion batteries. However, there are relatively serious volume expansion problems during their cycling process, which makes them face usage bottlenecks such as low initial Coulomb efficiency, low cycle capacity retention rate, short calendar life, and poor rate performance. Currently, the mainstream treatment method for silicon materials is to reduce the content of silicon and compound it with carbon to maintain a relatively high capacity. However, this type of method sacrifices the capacity advantage of silicon-based anode materials. Therefore, it is currently difficult to balance the relationship between high silicon loading and excellent cycle performance, which restricts the large-scale application of silicon-based anode materials. Summary of the Invention

[0004] In view of this, the embodiments of the present disclosure provide a copper / nitrogen co-doped multi-level silicon-carbon anode material and a preparation method thereof, which can solve the problems of serious volume expansion, low cycle capacity retention rate, poor performance, etc. existing in the prior art.

[0005] In a first aspect, the embodiments of the present disclosure provide a copper / nitrogen co-doped multi-level silicon-carbon anode material, including: A micron-scale porous silicon structure; the porous silicon structure is formed by stacking nano-silicon particles, and the porous silicon structure includes an inner core region, an intermediate region, and an outer peripheral region from the inside to the outside, and the pore diameters of the nano-pores in the inner core region, the intermediate region, and the outer peripheral region increase in sequence; A copper-graphene composite buffer layer, which includes a part coated outside the porous silicon structure and a part embedded in the nano-pores; A nitrogen-doped polydopamine carbon protection layer, which is coated outside the copper-graphene composite buffer layer.

[0006] Optionally, the copper-graphene composite buffer layer includes a plurality of graphene sheets and copper nanoparticles embedded between adjacent two graphene sheets, and the extending direction of the graphene sheets is consistent with the extending direction of the surface of the porous silicon structure where they are located.

[0007] Optionally, the composite buffer layer includes an inner buffer layer and an outer buffer layer. The copper content of the inner buffer layer is 15 wt% - 25 wt%, and the copper content of the outer buffer layer is 65 wt% - 75 wt%.

[0008] Optionally, the thickness of the nitrogen-doped polydopamine carbon protection layer is 20 nm - 30 nm; The nitrogen doping amount in the nitrogen-doped polydopamine carbon protection layer is 4% - 6%; The carbon content in the nitrogen-doped polydopamine carbon protection layer is 85% - 90%.

[0009] In a second aspect, an embodiment of the present disclosure provides a method for preparing a copper / nitrogen co-doped multi-stage silicon-carbon anode material for preparing the copper / nitrogen co-doped multi-stage silicon-carbon anode material, including: Heating and disproportionating the silicon monoxide powder in an inert atmosphere, and performing acid etching on the disproportionated silicon monoxide to obtain a porous silicon structure; Mixing the graphene dispersion liquid 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; Forming a first copper-graphene buffer layer outside the porous silicon structure through the first composite buffer slurry; Performing a modification treatment on the first copper-graphene buffer layer, and performing a coating treatment of a nitrogen-doped polydopamine carbon protection layer on the modified first copper-graphene buffer layer to obtain a copper / nitrogen co-doped multi-stage silicon-carbon anode material.

[0010] Optionally, before mixing the graphene dispersion liquid 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, it further includes: Mixing the graphene dispersion liquid 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, where the copper content in the second composite buffer slurry is less than the copper content in the first composite buffer slurry; Forming a second copper-graphene buffer layer 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 40 nm - 60 nm; the thickness of the second copper-graphene buffer layer is 20 nm - 30 nm.

[0011] Optionally, the preparation of the second copper-graphene network structure by mixing the graphene dispersion liquid and the copper salt precursor solution and adding a solvent to form a second composite buffer slurry containing the second copper-graphene network structure includes: Mix the prepared graphene dispersion liquid and the copper salt precursor solution in a ratio of 20:80 - 25:75, stir at a constant temperature of 60°C - 70°C for 3.5 h - 4.5 h to obtain a first mixed solution, add sodium hydroxide solution to the first mixed solution to adjust the pH to 10 - 11, and after centrifugation and washing, obtain a first solid product, and place the first solid product in ethanol to obtain the second composite buffer slurry; The particle size of the copper nanoparticles contained in the first solid product is 25 nm - 30 nm.

[0012] Optionally, the preparation of the first copper-graphene network structure by mixing the graphene dispersion liquid and the copper salt precursor solution and adding a solvent to form a first composite buffer slurry containing the first copper-graphene network structure includes: Mix the prepared graphene dispersion liquid and the copper salt precursor solution in a ratio of 70:30 - 80:20, stir at a constant temperature of 75°C - 80°C under a nitrogen atmosphere for 5.5 h - 6.5 h to obtain a second mixed solution, and successively perform centrifugation and washing on the second mixed solution to obtain a second solid product, and place the second solid product in ethanol to obtain the first composite buffer slurry; The particle size of the copper nanoparticles contained in the second solid product is 45 nm - 50 nm.

[0013] Optionally, the coating treatment of the modified first copper-graphene buffer layer with a nitrogen-doped polydopamine carbon protection layer to obtain a copper / nitrogen co-doped hierarchical silicon-carbon anode material includes: Successively perform heating, vacuum drying, and cleaning treatments on the modified first copper-graphene composite buffer layer to obtain a first material; Perform dopamine in-situ self-polymerization treatment on the first material to obtain a second material, and a dense and uniform polydopamine protection layer is formed on the outer side of the second material; Place the second material in a nitrogen atmosphere and perform heat treatment in a programmed heating manner, and the nitrogen atoms in the dopamine molecules are in-situ doped into the carbon network to obtain a third material; there are several active sites in the third material and the third material has a coating layer of a nitrogen-containing polydopamine carbon layer; Slowly cool the third material, and after cooling to room temperature, obtain the copper / nitrogen co-doped hierarchical silicon-carbon anode material.

[0014] In a third aspect, embodiments of the present disclosure provide a lithium-ion battery, including the copper / nitrogen co-doped hierarchical silicon-carbon anode material described above, or including a copper / nitrogen co-doped hierarchical silicon-carbon anode material prepared by using the preparation method of the copper / nitrogen co-doped hierarchical silicon-carbon anode material described above, and the copper / nitrogen co-doped hierarchical silicon-carbon anode material is the anode material of the lithium-ion battery.

[0015] The preparation method of the copper / nitrogen co-doped hierarchical silicon-carbon anode material disclosed in the present application can significantly improve the energy density of the lithium-ion battery by using a porous silicon structure. The porous silicon structure is formed by stacking nano-silicon particles, and these nano-silicon particles have a high specific surface area and can store more lithium ions, thereby improving the energy density of the battery and effectively alleviating the volume expansion problem of silicon materials during the cycling process; 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 can effectively disperse and absorb the volume changes during charge and discharge, thereby optimizing the structural stability of the material; by introducing a copper-graphene composite buffer layer, the stress generated by the silicon material during charge and discharge can be effectively absorbed and dispersed, thereby improving the cycling performance and capacity retention rate; the introduction of the copper-graphene composite buffer layer not only helps to alleviate volume expansion but also can improve the conductivity of the material. The combination of copper nanoparticles and graphene sheets forms an efficient conductive network, enabling lithium ions to be transported in the material faster, thereby improving the rate performance of the battery; by further coating a nitrogen-doped polydopamine carbon protective layer on the copper-graphene composite buffer layer, the silicon material can be effectively protected from external environmental erosion and oxidation, extending the service life of the battery. Through reasonable material design and composite processes, this method successfully balances the relationship between high silicon loading and excellent cycling performance. The combination of the porous silicon structure and the copper-graphene composite buffer layer not only retains the capacity advantage of the silicon material but also significantly improves its cycling performance, providing the possibility for the large-scale application of silicon-based anode materials.

[0016] The above description is only an overview of the technical solutions of the present disclosure. In order to understand the technical means of the present disclosure more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present disclosure more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings. Brief Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1Schematic flow chart of the preparation method of the copper / nitrogen co-doped multi-level silicon-carbon anode material provided by the embodiments of the present disclosure.

[0019] Figure 2 Schematic flow chart of the method for heating and disproportionating silicon monoxide powder in an inert atmosphere provided by the embodiments of the present disclosure.

[0020] Figure 3 Schematic flow chart of the method for modifying the first copper-graphene composite buffer layer provided by the embodiments of the present disclosure.

[0021] Figure 4 Schematic flow chart of the method for coating the modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material provided by the embodiments of the present disclosure.

[0022] Figure 5 For Figure 4 Flow chart of the acquisition method of the second material in

[0023] Figure 6 Schematic three-dimensional diagram of the copper / nitrogen co-doped multi-level silicon-carbon anode material provided by the embodiments of the present disclosure.

[0024] Figure 7 For Figure 6 Cross-sectional view in

[0025] Figure 8 For Figure 6 Cross-sectional view of the porous silicon structure in

[0026] Figure 9 For Figure 6 Schematic structural diagram of the copper-graphene composite buffer layer in

[0027] Figure 10 Scanning electron micrograph of silicon monoxide powder provided by the embodiments of the present disclosure.

[0028] Figure 11 Schematic diagram for comparing the XRD of silicon monoxide powder after etching with the original silicon monoxide and disproportionated silicon monoxide provided by the embodiments of the present disclosure.

[0029] Figure 12 Transmission electron micrograph of particles after coating the modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer provided by the embodiments of the present disclosure.

[0030] Figure 13 Spectrum diagram of Raman test on the composite material forming the first copper-graphene composite buffer layer after modification provided by the embodiments of the present disclosure.

[0031] Figure 14 This is the XPS spectrum of the material after the coated treatment of the modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer in the embodiments of the present disclosure.

[0032] Figure 15 This is a schematic diagram of the cycling performance of the composite material provided by the embodiments of the present disclosure in a half-cell.

[0033] Description of reference numerals: 10. Porous silicon structure; 11. Inner 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 protection layer. Detailed implementation manners

[0034] The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0035] It should be clear that the following uses specific specific examples to illustrate the implementation manners of the present disclosure, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. The present disclosure can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure.

[0036] It should be noted that the following describes various aspects of the embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present disclosure, those skilled in the art should 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 described herein can be used to implement the device and / or practice the method. In addition, this device can be implemented and this method can be practiced using other structures and / or functions in addition to one or more of the aspects described herein.

[0037] It should also be noted that the illustrations provided in the following embodiments only schematically illustrate the basic concept of the present disclosure. The diagrams only show the components related to the present disclosure, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in its actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0038] In addition, in the following description, specific details are provided 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.

[0039] Referring to Figure 1 , the first aspect of the present application discloses a method for preparing a copper / nitrogen co-doped multi-stage silicon-carbon anode material, including the following steps: S100, heating and disproportionating silicon monoxide powder in an inert atmosphere, and performing acid etching on the disproportionated silicon monoxide to obtain a porous silicon structure.

[0040] Among them, the porous silicon structure is formed by stacking a number of nanosilicon particles, and the pore diameters of the nanosilicon particles forming the nanopores form an inner core region, a middle region, and an outer peripheral region with increasing pore diameters from the inside to the outside. The overall porous silicon structure is at the micron level.

[0041] Among them, heating and disproportionating silicon monoxide powder in an inert atmosphere may include: heating silicon monoxide powder in an inert atmosphere at 800°C - 1200°C for 4h to 8h; the particle size of the silicon monoxide powder is 500nm - 15μm.

[0042] Specifically, referring to Figure 2 , for the method of "heating and disproportionating silicon monoxide powder in an inert atmosphere" in S100, it specifically includes: S111, heating silicon monoxide powder in an inert atmosphere at a rate of 5°C / min - 7°C / min to 500°C - 550°C and holding for 1 - 1.5 hours to obtain silicon monoxide with surface adsorbates removed; S112, then heating to 900°C - 950°C at a rate of 3°C / min - 43°C / min and holding for 2 - 2.5 hours to start the disproportionation of silicon monoxide; S113, finally heating to 1100°C - 1150°C at a rate of 2°C / min - 2.5°C / min and holding for 4 - 4.5 hours.

[0043] In this embodiment, a temperature-programmed heating method is adopted. Through the temperature control of A100, the surface adsorbates of the initial silicon monoxide powder are removed; through the temperature control of A200, the silicon monoxide after removing the surface adsorbates starts to disproportionate; through the temperature control of A300, deep disproportionation is completed. This stepped temperature control can promote the gradual conversion of silicon monoxide into a mixture of silicon and silicon dioxide, and form a preliminary layered structure at the microscale. This layered structure can effectively form a surface protection layer, release stress during the repeated expansion of electrode particles, reduce the pulverization probability of the electrode material, and significantly improve the cycling performance of the particles.

[0044] The microscopic structural characteristics of the disproportionation products directly determine the pore size distribution of the final porous silicon. In the temperature range of 900 - 1000 °C, silicon grains with relatively small particle sizes (20 - 30 nm) are mainly formed, and these grains will constitute the core region of the porous silicon; in the range of 1000 - 1050 °C, silicon grains with medium sizes (30 - 50 nm) are formed, corresponding to the middle region; while in the high-temperature range of 1050 - 1100 °C, silicon grains with larger sizes (50 - 80 nm) are formed, and these grains finally constitute the peripheral region. By precisely controlling the holding time in each temperature range, the quantity ratio of silicon grains in different regions can be regulated.

[0045] For the method of "performing acid etching on the disproportionated silicon monoxide to obtain a porous silicon structure" in S100, it includes: immersing the disproportionated silicon monoxide in a mixed acid solution and performing etching at a preset temperature to obtain a porous silicon structure.

[0046] The mixed acid solution is preferably a mixed solution of hydrochloric acid solution and hydrofluoric acid solution, and the ratio of the hydrochloric acid solution to the hydrofluoric acid solution is 1:5 - 1:2.

[0047] Among them, the pore diameter of the obtained porous silicon structure is preferably 1 nm - 20 nm.

[0048] Mixed acid etching is a key step in forming the final porous structure. For "performing acid etching on the disproportionated silicon monoxide to obtain a porous silicon structure" in S100, it includes: placing the disproportionated silicon monoxide in a mixed acid solution, mixing and stirring, reacting within the etching temperature range of -70 °C - 25 °C for 12 h - 36 h, and obtaining porous silicon after vacuum filtration.

[0049] Specifically, the disproportionation product can be immersed in a mixed solution of hydrochloric acid and hydrofluoric acid with a volume ratio of 1:3 and etched at -20°C. First, the low-temperature condition can effectively reduce the volatilization of hydrofluoric acid and ensure that the concentration of the etching solution is moderate. Second, the low-temperature condition is conducive to controlling the balanced reduction of the etching rate and ensuring the formation of a uniform pore structure. The etching process can be divided into three stages: in the first 4 hours, the silicon dioxide formed by natural oxidation in the peripheral region is mainly removed to form large pores with a size of 15 nm - 20 nm; in the next 8 hours, the middle region is etched to form medium pores with a size of 8 nm - 12 nm; in the last 12 hours, the core region is slowly etched to form micropores with a size of 3 nm - 5 nm. The entire process can be carried out with magnetic stirring at 400 rpm to ensure the uniformity of etching.

[0050] Furthermore, after the etching is completed, it can be washed successively with deionized water, ethanol, and acetone, with each solvent being washed 3 times to fully remove the residual acid solution and by-products. Finally, it is preferably dried in a vacuum environment at 60°C for 12 hours to obtain a porous silicon core material with a gradient pore size distribution. This multi-level 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 transmission of lithium ions and the volume expansion of silicon materials.

[0051] In this embodiment, the porous silicon structure obtained through S100 is divided into three regions from the inside to the outside: 1) the core region (diameter 2 μm - 3 μm): including densely arranged nanosilicon particles (particle size 20 nm - 30 nm), and the pore size of the nanopores formed by the nanosilicon particles in this region is preferably 3 nm - 5 nm, with a porosity of 15% - 20%; 2) the middle region (thickness 1.5 μm - 2 μm): including loosely arranged nanosilicon particles (particle size 30 nm - 50 nm), and the pore size of the nanopores formed by the nanosilicon particles in this region is preferably 8 nm - 12 nm, with a porosity of 25% - 30%; 3) the peripheral region (thickness 1 μm - 1.5 μm): including reticulated interconnected nanosilicon particles (particle size 50 nm - 80 nm), and the pore size of the nanopores formed by the nanosilicon particles in this region is preferably 15 nm - 20 nm, with a porosity of 35% - 40%.

[0052] The pore structure therein is a dendritic hierarchical pore, which gradually coarsens from the inside to the outside. This hierarchical pore that gradually coarsens from the inside to the outside can gradually relieve the particle deformation caused by the volume expansion of the particles during the cycling process, achieve the gradient release of stress, and thus form the effect of gradually increasing mechanical strength from the inside to the outside.

[0053] For example, the porous silicon structure obtained through S100 can be porous silicon particles with a pore diameter of 4 nm in the core region, 10 nm in the middle region, and 18 nm in the peripheral region. This gradient pore size distribution not only ensures the mechanical strength of the material but also lays a good foundation for the subsequent optimization of electrochemical performance.

[0054] S200: Mix the graphene dispersion liquid and the copper salt precursor solution to prepare a first copper-graphene network structure, and add a solvent to form a first composite buffer slurry containing the first copper-graphene network structure.

[0055] Specifically, 1) Mix the prepared graphene dispersion liquid and the copper salt precursor solution in a ratio of 70:30 - 80:20 to obtain a higher copper content; 2) Stir the mixture at a constant temperature of 75°C - 80°C under a nitrogen atmosphere for 5.5 h - 6.5 h to enable the copper nanoparticles to fully grow to a preset particle size. Here, the operation is carried out under a nitrogen atmosphere to prevent the copper nanoparticles from being oxidized and to facilitate the formation of a more complete conductive network structure; 3) After centrifuging and washing the second mixed solution in sequence, obtain a second solid product, and place the second solid product in ethanol to obtain the first composite buffer slurry.

[0056] The particle size of the copper nanoparticles contained in the second solid product is 45 nm - 50 nm.

[0057] S300: Form a first copper-graphene buffer layer outside the porous silicon structure through the first composite buffer slurry.

[0058] Specifically, place the porous silicon structure in the first composite buffer slurry, perform ultrasonic treatment, then carry out vacuum filtration, and after drying, perform heat treatment to obtain a structure including the porous silicon structure and the first copper-graphene buffer layer formed outside the porous silicon structure.

[0059] Furthermore, this application also includes: Before mixing the graphene dispersion liquid 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, it also includes: 1) Mix the graphene dispersion liquid and the copper salt precursor solution to prepare a second copper-graphene network structure, and add a solvent 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 that in the first composite buffer slurry; 2) Form a second copper-graphene buffer layer 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.

[0060] In this embodiment, the thickness of the first copper-graphene buffer layer is 40 nm - 60 nm; the thickness of the second copper-graphene buffer layer is 20 nm - 30 nm.

[0061] Among them, the copper-graphene composite buffer layer includes a copper-graphene network structure, and the copper-graphene network structure includes graphene sheets arranged parallel to the surface of the silicon particles, and copper nanoparticles are embedded in the gaps between the graphene sheets.

[0062] Among them, the second copper-graphene buffer layer is an inner buffer layer, which is mainly used to make full contact with the surface of the silicon particles in the porous silicon structure, so as to form a good interfacial bond with the porous silicon structure; the first copper-graphene buffer layer is an outer buffer layer, which is mainly used to provide an efficient electron transport channel.

[0063] In this embodiment, the method for preparing the graphene dispersion includes: dispersing graphene oxide in deionized water, controlling the concentration at 0.5 mg / mL, and performing ultrasonic treatment for 2 hours to form a stable dispersion, which is the required graphene dispersion.

[0064] The method for preparing the copper salt precursor solution includes: dissolving copper sulfate and ascorbic acid (mass ratio 1:2) in ethylene glycol to prepare the required copper salt precursor solution.

[0065] Specifically, 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, including: Mixing the prepared graphene dispersion and the copper salt precursor solution in a ratio of 20:80 - 25:75, stirring at a constant temperature of 60 °C - 70 °C for 3.5 h - 4.5 h to obtain a first mixed solution, adding sodium hydroxide solution to the first mixed solution to adjust the pH to 10 - 11, centrifuging and washing, obtaining a first solid product, and placing the first solid product in ethanol to obtain the second composite buffer slurry.

[0066] The particle size of the copper nanoparticles contained in the first solid product is 25 nm - 30 nm.

[0067] During the constant temperature stirring process, while ascorbic acid reduces copper ions, it also partially reduces graphene oxide.

[0068] Furthermore, in the second composite buffer slurry, the average particle size of the copper nanoparticles is about 30 nm.

[0069] In this embodiment, the porous silicon structure is first immersed in the prepared second composite buffer slurry. After ultrasonic treatment for 30 minutes to allow the slurry to fully penetrate into the pore structure and come into full contact with the surface of the silicon particles, vacuum filtration is carried out to form a uniform second copper-graphene buffer layer. After drying at 110°C - 130°C (preferably 120°C) for 2 - 3 hours (preferably 2 hours), an inner composite material is obtained. The inner composite material includes a porous silicon structure and a second copper-graphene buffer layer covering the porous silicon structure.

[0070] Among them, ultrasonic treatment helps to improve the permeability and distribution uniformity of the slurry in the pores of the porous silicon structure; during vacuum filtration, the second composite buffer slurry will be evenly coated on the silicon particles in the porous silicon structure to form a coating. In this inner composite material, the inner slurry forms a good interfacial bond with the porous silicon structure.

[0071] Then, the inner composite material is immersed in the first composite buffer slurry. After ultrasonic treatment for 30 minutes, vacuum filtration is carried out to form a uniform first copper-graphene buffer layer. After drying at 60°C - 80°C (preferably 80°C) for 2 - 3 hours (preferably 2 hours), a 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, it can be understood that the target sample includes a porous silicon structure and a copper-graphene composite buffer layer covering the porous silicon structure.

[0072] The final heat treatment process is crucial for optimizing the interfacial structure: specifically, in a hydrogen / argon (5:95) mixed atmosphere, the temperature is raised to 300°C at a rate of 2°C / min and held for 2 hours. This step can promote the formation of a stable interfacial bond between copper nanoparticles and graphene; the cooling process adopts natural cooling to reduce the generation of thermal stress.

[0073] 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). Among them, the inner layer can be understood as the first deposition layer obtained by placing the porous silicon structure in the inner slurry (i.e., the second composite buffer slurry), and the outer layer can be understood as the new deposition layer, that is, the second deposition layer, obtained after immersing the inner composite material in the outer slurry (i.e., the first composite buffer slurry). In this embodiment, the first deposition layer ensures a good interfacial bond with the porous silicon structure, and the second deposition layer can provide an efficient electron transport channel.

[0074] Through the process of S100 - S300, a copper-graphene composite buffer layer with stable structure and excellent electrical conductivity can be obtained.

[0075] 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 comprehensive performance. This pore size-thickness gradient structure design not only solves the problem of insufficient electrical conductivity of the traditional carbon coating layer but also provides excellent mechanical buffering effects.

[0076] For 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 protection layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material.

[0077] Specifically, the copper / nitrogen co-doped multi-level silicon-carbon anode material sequentially includes from the center to the outside: a porous silicon structure at the core, a first copper-graphene composite buffer layer coating the nano-silicon particles in the porous silicon structure, and a nitrogen-doped polydopamine carbon protection layer, wherein part of the copper nanoparticles are embedded in the peripheral pore channels of the porous silicon structure.

[0078] In this embodiment, surface modification and protection layer preparation are key steps to ensure the long-term stability of the composite material, and the core lies in constructing a chemically bonded interfacial structure and a functionalized protection layer.

[0079] Specifically refer to Figure 3 , the method of "modifying the first copper-graphene buffer layer" in S400 specifically includes: A100, determining a coupling agent.

[0080] In this embodiment, 3-aminopropyltriethoxysilane (APTES) is preferably used as the coupling agent.

[0081] A200, mixing the coupling agent with ethanol according to a mass percentage of 0.5%-0.7% to obtain a coupling agent ethanol solution.

[0082] Specifically, the copper-graphene composite buffer layer sample is immersed in an APTES ethanol solution of 0.5 wt%-0.7 wt% to obtain a coupling agent ethanol solution.

[0083] A300, immersing the copper-graphene composite buffer layer in the coupling agent ethanol solution and stirring at 40°C - 45°C for 2 - 2.5 hours to obtain a modified copper-graphene composite buffer layer.

[0084] Through this step, the alkoxy groups of the silane coupling agent undergo a condensation reaction with the hydroxyl groups on the material surface, and at the same time, active amino groups are introduced on the surface, providing reaction sites for the subsequent polymerization of dopamine.

[0085] Refer to Figure 4, the method of "coating the modified first copper-graphene buffer layer with a nitrogen-doped polydopamine carbon protection layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon anode material" in S400 specifically includes: B100, heating, vacuum drying, and cleaning the modified first copper-graphene composite buffer layer in sequence to obtain a first material.

[0086] Specifically, the sample is dried in a vacuum environment at 80°C - 85°C for 4 - 4.5 hours to promote the complete condensation and cross-linking of the silane coupling agent. Subsequently, it is repeatedly rinsed 3 times with absolute ethanol to remove unreacted APTES molecules. The key to this step is to control the density of surface amino groups. Excessive amino group density will cause the subsequent dopamine polymerization to be too fast, affecting the uniformity of the protection layer.

[0087] B200, performing in-situ self-polymerization treatment of dopamine on the first material to obtain a second material, and the outer side of the second material has a dense and uniform polydopamine protection layer.

[0088] Specifically refer to Figure 5 , the "method for obtaining the second material" in B200, which specifically includes: B210, placing both the first material and dopamine hydrochloride in the prepared Tris buffer solution to obtain a first solution.

[0089] Among them, the pH of the prepared Tris buffer solution is 8.5, and the concentration of the solution is 0.01 mol / L.

[0090] Specifically, the first material is dispersed in the Tris buffer solution, and at the same time, dopamine hydrochloride is dissolved in the buffer solution with a concentration controlled at 2 mg / mL to obtain a first solution.

[0091] B220, ultrasonically treating the first solution, adding 10 mL of dopamine solution dropwise to the treated first solution, and stirring with a magnetic stirrer for 24 hours to obtain a second material.

[0092] Specifically, in order to ensure the dispersion uniformity, ultrasonic treatment is performed for 15 minutes; then the dopamine solution is slowly added dropwise at room temperature, and the stirring speed of 400 rpm is maintained throughout the process; the polymerization reaction lasts for 24 hours.

[0093] The kinetic control of the polymerization process is extremely important. The first 4 hours is the nucleation stage, during which dopamine preferentially polymerizes at the surface amino group sites; the next 8 hours is the growth stage, and polydopamine gradually forms a complete coverage layer; the last 12 hours is the cross-linking stage, and more chemical cross-links are formed between the polymer chains to improve the mechanical strength of the protection layer. Throughout the process, the polymerization rate is adjusted by controlling the temperature (25 ± 2°C) and pH value (8.5 ± 0.1) to ensure the formation of a dense and uniform protection layer.

[0094] After the protective layer is formed, nitrogen doping treatment is required to improve the conductivity, so B300 is performed next.

[0095] In B300, the second material is placed in a nitrogen atmosphere and heat-treated in a programmed heating manner. The 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 of nitrogen-containing polydopamine carbon layer.

[0096] Specifically, first, it is heated to 200°C - 220°C at a rate of 5°C / min - 6°C / min and held for 1 - 1.2 hours to remove residual moisture; then it is heated to 400°C - 420°C at a rate of 3°C / min - 3.5°C / min and held for 2 - 2.5 hours. At this stage, polydopamine is converted into a nitrogen-containing carbon layer.

[0097] During the heat treatment process, the nitrogen atoms in the dopamine molecules are in-situ doped into the carbon network to form active sites such as pyridine nitrogen and pyrrole nitrogen.

[0098] In B400, the third material is slowly cooled, and after cooling to room temperature, a copper / nitrogen co-doped hierarchical silicon-carbon anode material is obtained.

[0099] In this embodiment, the final cooling process also needs to be precisely controlled. Specifically, a slow cooling rate of 2°C / min - 2.5°C / min can be adopted, which can reduce the generation of thermal stress and avoid cracking of the protective layer. After cooling to room temperature, the protective layer in the obtained copper / nitrogen co-doped hierarchical silicon-carbon anode material has the following characteristics: uniform thickness (25 ± 2 nm), moderate nitrogen doping amount (5 ± 0.5 at%), low surface roughness (Ra < 5 nm), and strong bonding with the substrate.

[0100] 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 can not only effectively prevent the excessive infiltration of the electrolyte, but also provide additional lithium storage sites through its unique nitrogen-doped structure, thereby improving the overall electrochemical performance of the material. Experiments have proved that this design can keep the material in a stable structural integrity during more than 100 cycles, which is an important guarantee for realizing high-performance lithium-ion battery anode materials.

[0101] Through the preparation method of the copper / nitrogen co-doped hierarchical silicon-carbon anode material disclosed in this application, the combination of the copper-graphene synergistic reinforcement structure and the gradient porous design not only solves the intrinsic problems of silicon materials, but also gives full play to the advantages of each component, forming a new composite material system with a complete logic and technical feasibility.

[0102] The preparation method of the 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 energy density of the battery and effectively alleviating the volume expansion problem of silicon materials during the cycling process. 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 the volume changes during charge and discharge, thus optimizing the structural stability of the material. By introducing a copper-graphene composite buffer layer, the stress generated by the silicon material during charge and discharge can be effectively absorbed and dispersed, thereby improving the cycling performance and capacity retention rate. The introduction of the copper-graphene composite buffer layer not only helps to alleviate volume expansion but also improves the conductivity of the material. The combination of copper nanoparticles and graphene sheets forms an efficient conductive network, enabling lithium ions to be transported faster in the material, thus improving the rate performance of the battery. By further coating a nitrogen-doped polydopamine carbon protective layer on the copper-graphene composite buffer layer, the silicon material can be effectively protected from external environmental erosion and oxidation, extending the service life of the battery. Through reasonable material design and composite processes, this method successfully balances the relationship between high silicon loading and excellent cycling performance. The combination of the porous silicon structure and the copper-graphene composite buffer layer not only retains the capacity advantage of the silicon material but also significantly improves its cycling performance, providing the possibility for the large-scale application of silicon-based anode materials.

[0103] In summary, the preparation method of the copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application has significant advantages in improving the energy density, cycling performance, rate performance, and calendar life of lithium-ion batteries, providing an effective solution to the bottleneck problems in the application of existing silicon-based anode materials.

[0104] Specifically, the preparation method of the copper / nitrogen co-doped multi-level silicon-carbon anode material disclosed in this application prepares a porous silicon structure formed by stacking nano-silicon particles through heating and disproportionation of silicon monoxide powder in an inert atmosphere and performing acid etching, and the pore diameter increases from the inside to the outside. This structural design not only increases the specific surface area of the material, but also helps to improve the mechanical strength and electrical conductivity of the material; by embedding copper nanoparticles in the gaps between graphene sheets to form a copper-graphene network structure, this composite buffer layer can effectively improve the electrical conductivity and thermal conductivity of the material, while enhancing the mechanical stability of the material; through the coating treatment of the nitrogen-doped polydopamine carbon protection layer, the chemical stability and mechanical durability of the material can be further improved, and at the same time, some functional properties can be imparted to the material, such as improving the antioxidant and corrosion resistance of the material; the different treatments and material selections of the inner layer and the outer layer enable the composite material to exhibit different performance characteristics in different application scenarios, and this design flexibility enhances the application range of the material; from the material selection, treatment to the final heat treatment and protection layer coating, each process is precisely controlled to ensure the stable performance and quality of the final product; the operation in an inert atmosphere and nitrogen atmosphere reduces environmental pollution and conforms to the trend of green manufacturing; due to its excellent electrical conductivity and structural stability, this copper / nitrogen co-doped multi-level 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, due to its high specific surface area and excellent mechanical properties, it can be used to enhance the performance of other materials.

[0105] Referring to Figure 6 and Figure 7 In the second aspect, a copper / nitrogen co-doped multi-level silicon-carbon anode material prepared by 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 protection layer 30 covering the outside of the copper-graphene composite buffer layer. Among them, the total diameter of the porous silicon structure is preferably 5 μm - 8 μm, and the porosity of the porous silicon structure is 15% - 20%.

[0106] In this embodiment, taking the overall outer diameter of the copper / nitrogen co-doped multi-level silicon-carbon anode material as 6 μm as an example, preferably, in the porous silicon structure as the core layer, the diameter of the inner core area is 2.5 μm, the pore diameter of the nano-pores in the inner core area is 4 nm, and the porosity in the inner core area is 18%; the thickness of the middle area is 1.8 μm, the pore diameter of the nano-pores in the middle area is 10 nm, and the porosity in the middle area is 28%, the thickness of the outer peripheral area is 1.2 μm, the pore diameter of the nano-pores in the outer peripheral area is 18 nm, and the porosity in the outer peripheral area is 38%.

[0107] In the copper-graphene composite buffer layer as the intermediate layer, the inner layer preferably has a size of 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 preferably has a size of 50 nm, and the copper content in the outer layer is preferably 70 wt%.

[0108] The nitrogen-doped polydopamine carbon protective layer is coated on the outside of the copper-graphene composite buffer layer. The thickness of the nitrogen-doped polydopamine carbon protective layer is 20 nm - 30 nm. In its compositional characteristics, the nitrogen doping amount in the nitrogen-doped polydopamine carbon protective layer is 4% - 6%, and the carbon content in the nitrogen-doped polydopamine carbon protective layer is 85% - 90%; the residual functional groups include hydroxyl groups and amino groups for interfacial bonding; the structural characteristics of the nitrogen-doped polydopamine carbon protective layer: the density > 95%, and the surface roughness Ra < 5 nm; the coating integrity: there is no exposed area.

[0109] Further, the thickness of the nitrogen-doped polydopamine carbon protective layer as the outer layer is preferably 25 nm, the nitrogen doping amount therein is preferably 5.2 at%, and the surface roughness is preferably 3.8 nm.

[0110] Specific example: a nitrogen-doped polydopamine carbon protective layer with a thickness of 25 nm and a nitrogen doping amount of 5 at%. The interfacial structure design includes: 1) the inner core layer / intermediate layer interface: the width of the transition zone of this interface is 10 - 15 nm. Among them, copper nanoparticles are partially embedded in the pores of the outer peripheral region of the porous silicon, and Si-O-Cu bonding is formed at this interface; 2) the intermediate layer / outer layer interface: the width of the transition zone is 5 - 8 nm, and covalent bonding is formed through amino groups and hydroxyl groups, having a gradient chemical composition.

[0111] This structural design realizes the synergistic optimization of mechanical properties and electrochemical properties by precisely controlling the parameters of each layer and interfacial characteristics, providing a new design idea for high-performance silicon-based anode materials.

[0112] Refer to Figure 8 , the porous silicon structure is formed by stacking a number of nanosilicon particles, and the pore diameters of the nanoholes formed by the number of nanosilicon particles form an inner core region 11, an intermediate region 12, and an outer peripheral region 13 with increasing pore diameters from inside to outside. The overall porous silicon structure is at the micron level.

[0113] In the porous silicon structure, the porosity increases from inside to outside, and the pore diameters of the nanoholes increase from inside to outside.

[0114] The pore diameters of the nanoholes in the inner core region are 3 nm - 5 nm, the porosity in the inner core region is 15% - 20%, and the diameter of the inner core region is 2 μm - 3 μm; the pore diameters of the nanoholes in the intermediate region are 8 nm - 12 nm, the porosity in the intermediate region is 25% - 30%, and the thickness of the intermediate region is 1.5 μm - 2 μm; the pore diameters of the nanoholes in the outer peripheral region are 15 nm - 20 nm, the porosity in the outer peripheral region is 35% - 40%, and the thickness of the outer peripheral region is 1 μm - 1.5 μm.

[0115] Referring to Figure 9 , the copper-graphene composite buffer layer (i.e., the copper-graphene synergistically enhanced composite buffer layer) includes a copper-graphene network structure. The copper-graphene network structure includes graphene sheets arranged in an orientation parallel to the surface of the 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.

[0116] In this embodiment, the copper-graphene composite buffer layer includes an inner layer and an outer layer. Among them, the preferred particle size of copper in the inner layer is 30 nm, the inner layer is mainly composed of graphene sheets with a sheet size of 0.5 μm - 1 μm; the preferred particle size of copper in the outer layer is 50 nm, and the outer layer is still mainly composed of graphene sheets with a sheet size of 1 μm - 2 μm.

[0117] The total thickness of the copper-graphene composite buffer layer is preferably 75 nm, and the continuity of the conductive grid is preferably greater than 95%.

[0118] It should be noted that Figures 6 to 9 The schematic diagram provided only for facilitating the understanding of the structure does not limit the protection scope of the present application.

[0119] Furthermore, referring to Figure 10 , the figure shows a scanning electron microscope image of the silicon monoxide powder provided by the embodiment of the present disclosure. Using the silicon monoxide particles shown in the figure as the precursor material for high-temperature disproportionation, the average diameter of the particles is 10 microns, and the edges of the particles in the electron microscope image are not clear, indicating that the conductivity of the unmodified silicon monoxide material is poor.

[0120] Referring to Figure 11 , the figure shows a schematic diagram for comparing the XRD of the etched silicon monoxide powder with the original silicon monoxide and the silicon monoxide after disproportionation treatment provided by the embodiment of the present disclosure. Among them, m-SiO is the XRD pattern of the original silicon monoxide particles, d-SiO is the XRD pattern of the silicon monoxide after disproportionation, and p-Si is the XRD pattern of the etched silicon monoxide. There is a peak envelope in the XRD pattern of m-Si, representing that the original silicon monoxide particles are in an amorphous state without obvious crystallization characteristics; after disproportionation treatment, as can be seen from the pattern of d-SiO, obvious crystal characteristics appear inside the particles after high-temperature treatment, and the peaks are relatively sharp with a high degree of crystallization, but there are still peak envelopes in the pattern, representing that there is still a small amount of amorphous silicon monoxide after high-temperature disproportionation, which will significantly affect the cycle capacity of the material; subsequently, after the etching process, as can be seen from the pattern of p-Si, the amorphous silicon monoxide has been completely removed and the crystalline silicon has been well retained.

[0121] Referring to Figure 12, which is a transmission electron microscope image of the particles after coating the modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer; the core layer and the outer carbon layer structure of the particles in the example can be clearly distinguished in the figure. By reasonable parameter control, the carbon layer thickness is adjusted to about 25 nm.

[0122] Referring to Figure 13 , which is a spectrogram of the Raman test on the composite material that forms the first copper-graphene composite buffer layer after modification treatment provided by the embodiment of the present disclosure; from the D / G ratio in the figure, it can be seen that in the prepared composite material, the D peak is relatively high, indicating that there are still many defects in the graphene in the prepared material and the degree of graphitization is relatively low.

[0123] Referring to Figure 14 This is an XPS energy spectrum diagram of the material after coating the modified first copper-graphene composite buffer layer with a nitrogen-containing polydopamine carbon layer provided by the embodiment of the present disclosure; the elemental peak positions of O, N, C, and Si can be seen in the figure, indicating that the nitrogen-containing dopamine has been successfully coated on the surface of the material to form an effective interfacial protection layer.

[0124] Referring to Figure 15 , which shows a schematic diagram of the cycling performance of the composite material in a half-cell provided by the embodiment of the present disclosure; the initial discharge capacity of this embodiment is 1386.12 mAh g -1 And as the number of cycling increases, the discharge capacity slightly increases. The cycling capacity after 100 cycles can reach 1496.02 mAh g -1 , and the charge-discharge efficiency within 100 cycles remains at 100%, showing excellent cycling performance.

[0125] On the other hand, the present application discloses a lithium-ion battery, which includes the copper / nitrogen co-doped multi-stage silicon-carbon anode material described above, or includes a copper / nitrogen co-doped multi-stage silicon-carbon anode material prepared by using the preparation method of the copper / nitrogen co-doped multi-stage silicon-carbon anode material, and the copper / nitrogen co-doped multi-stage silicon-carbon anode material is the anode material of the lithium-ion battery.

[0126] The basic principles of the present disclosure have been described above in combination with specific embodiments. However, it should be noted that the advantages, advantages, effects, etc. mentioned in the present disclosure are only examples and not limitations, and it cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present disclosure. In addition, the above-mentioned specific details are only for the purpose of illustration and easy understanding, rather than limitations. The above details do not limit the present disclosure to necessarily adopt the above specific details to implement.

[0127] In this disclosure, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The block diagrams of the devices, apparatuses, equipment, and systems involved in this disclosure are only illustrative examples and do not intend to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any way. Words such as "including", "comprising", "having", etc. are open-ended words, meaning "including but not limited to", and can be used interchangeably with each other. The words "or" and "and" used herein refer to the word "and / or", and can be used interchangeably with each other, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to", and can be used interchangeably with each other.

[0128] In addition, as used herein, "or" in the listing of items starting with "at least one" indicates a disjunctive listing, so that for example, the listing of "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 term "exemplary" does not mean that the examples described are preferred or better than other examples.

[0129] It should also be noted that in the systems and methods of this disclosure, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent solutions of this disclosure.

[0130] Various changes, substitutions, and alterations to the technologies described herein can be made without departing from the teachings defined by the appended claims. In addition, the scope of the claims of this disclosure is not limited to the specific aspects of the processes, machines, manufactures, compositions of events, means, methods, and acts described above. Current or later-developed processes, machines, manufactures, compositions of events, means, methods, or acts that perform substantially the same function or achieve substantially the same result as the corresponding aspects described herein can be utilized. Accordingly, the appended claims include such processes, machines, manufactures, compositions of events, means, methods, or acts within their scope.

[0131] 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 can 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 the broadest scope consistent with the principles and novel features disclosed herein.

[0132] The foregoing description has been presented for purposes of illustration and description. In addition, the description is not intended to limit embodiments of the present disclosure to the form disclosed herein. Although several example aspects and embodiments have been discussed above, those skilled in the art will recognize some variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A copper / nitrogen co-doped multi-level silicon-carbon negative electrode material, characterized in that: include: A micrometer-scale porous silicon structure; the porous silicon structure is formed by stacking nano-silicon particles, and the porous silicon structure includes a core region, a middle region, and a peripheral region from the inside to the outside, and the apertures of the nanopores in the core region, the middle region, and the peripheral region increase in sequence; A copper-graphene composite buffer layer, comprising a portion coated outside the porous silicon structure and a portion embedded in the nanopores; The nitrogen-doped polydopamine carbon protective layer is coated on the outer side of the copper-graphene composite buffer layer.

2. The copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 1, characterized in that: The copper-graphene composite buffer layer comprises a plurality of graphene sheets and copper nanoparticles embedded between two adjacent graphene sheets. The extending direction of the graphene sheets is consistent with the extending direction of the surface of the porous silicon structure where the graphene sheets are located.

3. The copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 2, characterized in that: The composite buffer layer comprises an inner buffer layer and an outer buffer layer, the inner buffer layer has a copper content of 15wt%-25wt%, and the outer buffer layer has a copper content of 65wt%-75wt%.

4. The copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 1, characterized in that: The thickness of the nitrogen-doped polydopamine carbon protective layer is 20nm-30nm; The nitrogen doping 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%.

5. A method for preparing a copper / nitrogen co-doped multi-level silicon-carbon negative electrode material, used to prepare the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to any one of claims 1 to 4, characterized in that: include: The silicon monoxide powder is heated and disproportionated in an inert atmosphere, and the disproportionated silicon monoxide is subjected to acid etching to obtain a porous silicon structure; Mixing a graphene dispersion and a copper salt precursor solution to prepare a first copper-graphene network structure, and adding a solvent to form a first composite buffer slurry including the first copper-graphene network structure; Forming a first copper-graphene buffer layer outside the porous silicon structure by using a first composite buffer slurry; 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 negative electrode material.

6. The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 5, characterized in that: 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 method further includes: Mixing a graphene dispersion and a copper salt precursor solution to prepare a second copper-graphene network structure, adding a solvent 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 the copper content in the first composite buffer slurry; Forming a second copper-graphene buffer layer outside the porous silicon structure by using 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; the thickness of the second copper-graphene buffer layer is 20nm-30nm.

7. The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 6, characterized in that: The graphene dispersion 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, comprising: The prepared graphene dispersion and the copper salt precursor solution are mixed in a ratio of 20:80-25:75, and stirred at a constant temperature of 60° C.-70° C. for 3.5 h-4.5 h to obtain a first mixed solution, and sodium hydroxide solution is added dropwise to the first mixed solution to adjust the pH to 10-11, and the first solid product is obtained after centrifugation and washing, 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 nm to 30 nm.

8. The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 7, characterized in that: The graphene dispersion 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, comprising: The prepared graphene dispersion and the copper salt precursor solution are mixed in a ratio of 70:30-80:20, and stirred at a constant temperature of 75° C.-80° C. in a nitrogen atmosphere for 5.5 h-6.5 h to obtain a second mixed solution, and the second mixed solution is centrifuged and washed 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 nm-50 nm.

9. The method for preparing the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material according to claim 5, characterized in that: The first copper-graphene buffer layer after the modification is coated with a nitrogen-doped polydopamine carbon protective layer to obtain a copper / nitrogen co-doped multi-level silicon-carbon negative electrode material, comprising: The first copper-graphene composite buffer layer after the modification is heated, vacuum dried, and cleaned in sequence to obtain a first material; Performing an in-situ dopamine self-polymerization treatment on the first material to obtain a second material, wherein the outer side of the second material has a dense and uniform polydopamine protective layer; The second material is placed in a nitrogen atmosphere and subjected to a heat treatment by a programmed temperature rise method, so that the 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 the third material has a coating layer of a nitrogen-containing polydopamine carbon layer; The third material is slowly cooled to room temperature to obtain the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material.

10. A lithium ion battery, characterized in that: It includes the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material described in any one of claims 1-4, or includes the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material prepared by the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material preparation method described in any one of claims 5-9, and the copper / nitrogen co-doped multi-level silicon-carbon negative electrode material is a negative electrode material for a lithium-ion battery.

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