Three-dimensional cross structure silicon-carbon composite material based on photovoltaic silicon sludge as well as preparation method and application of three-dimensional cross structure silicon-carbon composite material

Abstract

The invention belongs to the technical field of lithium ion battery negative electrode materials, and particularly discloses a three-dimensional cross structure silicon-carbon composite material based on photovoltaic silicon sludge and a preparation method and application thereof. The preparation method comprises the following steps: carrying out acid leaching on waste silicon powder generated in a photovoltaic silicon sludge cutting process by using an acid leaching solution, and then filtering, washing, drying and screening to obtain flaky silicon powder; the preparation method comprises the following steps: dissolving a binder in deionized water to form a solution, adding a dispersant, uniformly mixing to form aqueous slurry, adding flaky silicon powder, and uniformly mixing to obtain silicon slurry; carrying out spray drying treatment on the silicon slurry to obtain silicon microspheres; and carrying out coating treatment on the silicon microspheres by adopting a carbon source, and then sequentially carrying out stabilizing treatment and carbonization treatment in an inert atmosphere to obtain the continuous carbon-coated three-dimensional cross structure silicon-carbon composite material. The silicon-carbon composite material with the three-dimensional cross structure, which is obtained by the preparation method disclosed by the invention, has the advantages of an internal support framework constructed by three-dimensional cross stacking, uniform microsphere particle size, regular morphology, good fluidity and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, and particularly relates to a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon sludge and a preparation method and application thereof. BACKGROUND

[0002] Silicon-based materials are considered as important candidate materials for breaking through the energy density limit of commercial graphite negative electrodes due to their extremely high theoretical specific capacity (about 4200 mAh / g), and have key significance for the development of the next generation of high-energy-density lithium ion batteries. Under the current trend of electrification, developing silicon-based negative electrodes with high cycle stability and low cost has become a research focus in the field of energy storage materials. At the same time, a large amount of silicon powder waste generated in the cutting process of photovoltaic crystalline silicon has gradually become an important resource material for negative electrodes due to its high atomic purity, low impurity content, wide source and significantly lower cost than synthetic silicon. This kind of waste silicon can be used in battery material systems without complex purification, which is expected to promote the low-cost and green cycle development of silicon-based negative electrodes and has good industrialization potential.

[0003] However, the inherent irregular flaky morphology and high specific surface area of the cutting waste silicon in the crystalline silicon cutting process of the photovoltaic industry also bring a series of challenges to its actual application: the flaky particles are prone to stacking and agglomeration, the internal electrode lacks sufficient buffer space, the volume expansion stress is difficult to release during charging and discharging, leading to structural rupture and active material pulverization; the complex surface morphology and high activity make it difficult for the carbon coating layer to form continuously and uniformly, and incomplete coating and interruption of the conductive network are prone to occur, which seriously affects the cycle and rate performance of the material; in addition, during high-temperature heat treatment, irregular silicon sheets are prone to fusion and densification, resulting in a decrease in specific surface area and blockage of ion transport channels, further restricting the electrochemical reaction. The above shortcomings in structure construction and interface regulation seriously limit the efficient conversion of photovoltaic cutting waste silicon into high-performance silicon-based negative electrodes.

[0004] Therefore, it is urgent to develop a structure design and carbon composite integrated method suitable for the physical characteristics of this kind of silicon waste, aiming to construct a stable composite structure with three-dimensional buffer space, which can effectively inhibit particle agglomeration and realize uniform carbon coating, thereby significantly improving its cycle stability and rate performance, and laying a foundation for its practical application in lithium ion batteries. SUMMARY

[0005] In view of the above problems, the application discloses a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud, a preparation method and application thereof. The application forms a stable three-dimensional cross-frame by spraying and drying the silicon slurry made of a binder, a dispersant and flaky silicon powder, and realizes the formation of the spherical flaky silicon. The three-dimensional cross-structure silicon-carbon composite material prepared by the preparation method has the advantages of uniform microsphere particle size, regular morphology and good fluidity, and has a high bulk density and a suitable pore structure, is suitable for slurry coating and electrode compaction process, significantly improves the processability and industrial application compatibility of the material, and can realize the synergistic doping of elements such as B and N to realize performance regulation.

[0006] To solve the above problems, the application provides a preparation method of a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud, which comprises the following steps: S1. Waste silicon powder generated in the cutting process of photovoltaic silicon mud is subjected to acid immersion in an acid immersion liquid, and then is filtered, washed, dried and sieved to obtain flaky silicon powder; It should be noted that the purpose of acid immersion in the acid immersion liquid is to remove impurities. S2. A binder is dissolved in deionized water to form a solution, a dispersant is added and uniformly mixed to form an aqueous slurry, and then the flaky silicon powder is added and uniformly mixed to obtain a silicon slurry; wherein the content of the flaky silicon powder in the silicon slurry is 1-10wt%. S3. The silicon slurry is subjected to spray drying treatment to obtain silicon microspheres; wherein the inside of the silicon microspheres comprises a three-dimensional support framework composed of interlaced stacking of flaky silicon. S4. The silicon microspheres are coated with a carbon source, and then are sequentially subjected to stabilization treatment and carbonization treatment in an inert atmosphere to obtain a three-dimensional cross-structure silicon-carbon composite material coated with continuous carbon.

[0007] Preferably, in step S1, the acid immersion liquid is any one of hydrochloric acid and hydrofluoric acid, and the concentration is 0.5-2.0mol·L -1 , and the acid immersion time is 0.5-2h; the sieving is sieving through a 200-mesh sieve, and the flaky silicon powder has a flake diameter of less than 75μm.

[0008] Preferably, in step S2, the binder is at least one of carboxymethyl cellulose sodium and polyvinyl alcohol, and the content is 1-10wt% of the silicon slurry; and the dispersant is polyvinylpyrrolidone, and the content is 0.5-3wt% of the silicon slurry.

[0009] Preferably, in step S2, boric acid or borax also needs to be added to the aqueous slurry, and the mass ratio of the boric acid or borax to the binder is 0.05-0.5.

[0010] It should be noted that the purpose of further adding boric acid or borax in the aqueous slurry is to form a borate cross-linked structure, so as to improve the ball strength and anti-swelling property.

[0011] An exemplary mechanism of borax and sodium carboxymethyl cellulose (binder) forming a borate cross-linked structure is shown in the figure. Figure 1

[0012] Preferably, in step S2, urea is further added in the aqueous slurry, and the content of the urea is 15-25wt% of the silicon slurry.

[0013] It should be noted that the urea will volatilize in the subsequent stabilization treatment and carbonization treatment under inert atmosphere, so as to increase the direct spacing of the sheet silicon and provide more buffer space for the silicon expansion.

[0014] Preferably, in step S3, the spray drying inlet temperature of the spray drying treatment is 210-235℃, and the spray drying outlet temperature is 95-100℃.

[0015] Preferably, in step S4, the carbon source is at least one of polyacrylonitrile, polyaniline and polyamide acid; the coating treatment comprises dispersing the silicon microspheres in a carbon source solution and mixing uniformly; the solvent in the carbon source solution is at least one of N,N-dimethylformamide and N,N-dimethylacetamide, and the content of the carbon source is 5-10wt% of the carbon source solution; the mass ratio of the silicon microspheres to the carbon source is 1:1-2; the stabilization treatment is specifically: 240-280℃ for 0.5-1h in air atmosphere; the carbonization treatment under inert atmosphere is specifically: 750-900℃ for 0.5-2h in nitrogen or argon atmosphere.

[0016] Preferably, in step S4, the coating treatment further comprises adding 10000-mesh ultra-fine graphite powder; and the mass ratio of the silicon microspheres, the carbon source and the 10000-mesh ultra-fine graphite powder is 1:1-2:1.

[0017] Based on the same inventive concept, the application further provides a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud, which is prepared by the preparation method.

[0018] Based on the same inventive concept, the application further provides an application of the three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud in a lithium ion negative electrode material.

[0019] Compared with the prior art, the application has the following beneficial effects: ​(1) The present application forms an internal support framework by three-dimensional cross-stacking of sheet silicon, forming a structure with flexible buffer space. The sheet silicon is overlapped in a cross and inclined manner, and can release the volume expansion stress along the inter-sheet gap direction during lithiation, effectively avoiding the pulverization and structure rupture caused by the volume limitation of traditional bulk silicon, thereby significantly improving the structural stability and cycle life of the material; (2) The present application allows the sheet silicon to naturally form a multi-scale hierarchical pore structure during the interlaced stacking process, including macro-pore, meso-pore and micro-pore channels. The hierarchical pore system shortens the ion diffusion path, reduces the transmission resistance, and at the same time improves the wettability of the electrolyte, so that the SEI film can be uniformly generated on the surface and remain stable, thereby realizing a more efficient electrochemical reaction process; (3) The present application forms a continuous and dense carbon layer on the surface of the silicon microspheres through carbon coating and subsequent stabilization and carbonization treatment, and can add ultra-fine graphite during the carbon coating process, and build a three-dimensional conductive and mechanical support network through the internal graphite conductive skeleton and cross silicon sheet support. The composite system can absorb volume change and maintain structural integrity during charging and discharging, significantly reduce the volume expansion strain, and improve the capacity retention rate and cycle stability; (4) The carbon coating layer and the nitrogen (derived from the carbon source) and boron-doped carbon interface of the present application can reduce the formation energy of the SEI film and inhibit the decomposition of the electrolyte and the side reaction. The low surface curvature of the cross sheet silicon is conducive to the formation of a uniform and dense SEI film; the crosslinking and solidification of sodium carboxymethyl cellulose and borax and the subsequent carbon coating structure further enhance the interface stability and improve the film layer reliability during the electrochemical cycle process; (5) The present application forms a stable three-dimensional cross-frame by preparing a silicon slurry from a binder, a dispersing agent and sheet silicon powder, and realizing the formation of sheet silicon microspheres by spray drying. The three-dimensional cross-structure silicon-carbon composite material prepared by the preparation method of the present application has the advantages of uniform particle size, regular morphology and good flowability, and has high bulk density and suitable pore structure, which is suitable for slurry coating and electrode compaction process, significantly improving the processability and industrial application compatibility of the material, and realizing the synergistic doping of elements such as B and N in the interior to realize performance regulation. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the mechanism of borax and binder forming borate ester crosslinking structure in the present application; Figure 2 It is an XRD comparison chart of raw materials, intermediate materials and final products of Example 1 of the present application; Figure 3 It is an SEM graph of the silicon-carbon composite material prepared in Example 1 of the present application; (a) is an SEM graph with a scale of 1 μm; (b) is an SEM graph with a scale of 10 μm; Figure 4 The charge-discharge performance curve of the lithium battery assembled by the silicon-carbon composite material prepared in Example 1 of the present application; Figure 5 The cycle curve of the lithium battery assembled by the silicon-carbon composite material prepared in Example 1 of the present application; Figure 6 The cycle curve of the lithium battery assembled by the silicon-carbon composite material prepared in Example 2 of the present application; Figure 7 The cycle curve of the lithium battery assembled by the silicon microspheres prepared in Comparative Example 1 of the present application; Figure 8 The cycle curve of the lithium battery assembled by the composite material prepared in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0021] In order to make the present application more easily understood, the present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without making creative efforts are within the scope of protection of the present application. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved in the present application can be purchased from the market or prepared by the known methods.

[0022] In order to solve the challenges of the irregular flaky morphology and high specific surface area of the cutting waste silicon inherent in the crystalline silicon cutting process in the existing photovoltaic industry. The present application provides a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud and a preparation method and application thereof.

[0023] The present application will be further described below in conjunction with specific examples and comparative examples.

[0024] Example 1 A preparation method of a three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud, comprising the following steps: (1) selecting the waste silicon powder generated in the cutting process of photovoltaic silicon mud, adding 1.0 mol·L -1 of hydrochloric acid solution for 2 h to remove surface oxides and metal impurities; after the soaking, the solid is filtered and washed with deionized water until the washing liquid pH≈7, and then dried in a vacuum oven. The dried silicon powder is sieved through a 200 mesh sieve to obtain flaky silicon powder for use; (2) Dissolve sodium carboxymethyl cellulose (CMC) in deionized water and stir to form a transparent solution. Then add polyvinylpyrrolidone (PVP) to the solution and stir thoroughly to disperse it evenly. Then add urea and borax (to form a borate ester crosslinking structure) and stir thoroughly to disperse it evenly to obtain an aqueous slurry. Then add the flake silica powder from step (1) and continue stirring for 1 hour. Then use a high-speed disperser to disperse the agglomerated particles at a speed of 10,000 rpm for 30 minutes to further break up the agglomerated particles and obtain a uniform and stable silica slurry. The flake silica powder content in the silica slurry is 3 wt%, sodium carboxymethyl cellulose (CMC) is 5 wt%, polyvinylpyrrolidone (PVP) is 0.5 wt%, urea is 20 wt%, and borax is 0.5 wt%. (3) The silicon slurry is fed into a spray dryer for drying. The inlet temperature of the spray dryer is set to 220℃ and the outlet temperature is set to 98℃. After drying, silicon microspheres with an average particle size of 2-10μm are obtained. (4) The above-mentioned silicon microspheres were dispersed in a polyacrylonitrile (PAN) solution with a concentration of 8 wt% (solvent is N,N-dimethylformamide), and the surface of the silicon microspheres was uniformly coated by mechanical stirring. Then the sample was dried to remove the solvent. The dried sample was placed in an air atmosphere and stabilized at 240°C for 1.0 h, and then carbonized at 800°C in an Ar atmosphere for 2 h to obtain silicon-carbon composite microspheres with a continuous carbon coating on the outer layer. The mass ratio of silicon microspheres to polyacrylonitrile (PAN) was 1:1.

[0025] Example 2 A method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud includes the following steps: (1) Select waste silicon powder generated during the photovoltaic silicon mud cutting process and add 1.0 mol·L -1 The solid was soaked in hydrochloric acid solution for 2 hours to remove surface oxides and metallic impurities. After soaking, the solid was filtered and washed with deionized water until the pH of the washing solution was approximately 7. It was then dried in a vacuum oven. The dried silicon powder was then sieved through a 200-mesh sieve to obtain flake silicon powder for later use. (2) Dissolve sodium carboxymethyl cellulose (CMC) in deionized water and stir to form a transparent solution. Then add polyvinylpyrrolidone (PVP) to the solution and stir thoroughly to disperse it evenly to obtain an aqueous slurry. Then add the flake silica powder from step (1) and continue stirring for 1 hour. Then use a high-speed disperser to disperse the agglomerated particles at a speed of 10,000 rpm for 30 minutes to further break up the agglomerated particles and obtain a uniform and stable silica slurry. The flake silica powder content in the silica slurry is 5 wt%, sodium carboxymethyl cellulose (CMC) is 10 wt% of the silica slurry, and polyvinylpyrrolidone (PVP) is 1 wt% of the silica slurry. (3) The silicon slurry is fed into a spray dryer for drying. The inlet temperature of the spray dryer is set to 220℃ and the outlet temperature is set to 98℃. After drying, silicon microspheres with an average particle size of 2-10μm are obtained. (4) The above-mentioned silicon microspheres were dispersed in a 10wt% polyacrylonitrile (PAN) solution (solvent being N,N-dimethylformamide), and 10,000 mesh ultrafine graphite powder was added to it. The surface of the silicon microspheres was uniformly coated by mechanical stirring, and then dried to remove the solvent. The dried sample was placed in an air atmosphere and stabilized at 250°C for 1.0 h, and then carbonized at 800°C in an Ar atmosphere for 2 h to obtain silicon-carbon composite microspheres with a continuous carbon coating on the outer layer. The mass ratio of silicon microspheres, polyacrylonitrile (PAN) to 10,000 mesh ultrafine graphite powder was 1:2:1.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that the flake silicon powder is only spray-dried into spheres without outer carbon coating. The specific preparation method is as follows: A method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud includes the following steps: (1) Select waste silicon powder generated during the photovoltaic silicon mud cutting process and add 1.0 mol·L -1 The solid was soaked in hydrochloric acid solution for 2 hours to remove surface oxides and metallic impurities. After soaking, the solid was filtered and washed with deionized water until the pH of the washing solution was approximately 7. It was then dried in a vacuum oven. The dried silicon powder was then sieved through a 200-mesh sieve to obtain flake silicon powder for later use. (2) Dissolve sodium carboxymethyl cellulose (CMC) in deionized water and stir to form a transparent solution. Then add polyvinylpyrrolidone (PVP) to the solution and stir thoroughly to disperse it evenly. Then add urea and borax (to form a borate ester crosslinking structure) and stir thoroughly to disperse it evenly to obtain an aqueous slurry. Then add the flake silica powder from step (1) and continue stirring for 1 hour. Then use a high-speed disperser to disperse the agglomerated particles at a speed of 10,000 rpm for 30 minutes to further break up the agglomerated particles and obtain a uniform and stable silica slurry. The flake silica powder content in the silica slurry is 3 wt%, sodium carboxymethyl cellulose (CMC) is 5 wt%, polyvinylpyrrolidone (PVP) is 0.5 wt%, urea is 20 wt%, and borax is 0.5 wt%. (3) The silicon slurry is fed into a spray dryer for drying. The inlet temperature of the spray dryer is set to 220°C and the outlet temperature is set to 98°C. After drying, silicon microspheres with an average particle size of 2-10 μm are obtained.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that the flake silicon powder is only spray-dried into spheres with an outer carbon coating, and is not spray-dried into spheres. The specific preparation method is as follows: (1) Select waste silicon powder generated during the photovoltaic silicon mud cutting process and add 1.0 mol·L -1 The solid was soaked in hydrochloric acid solution for 2 hours to remove surface oxides and metallic impurities. After soaking, the solid was filtered and washed with deionized water until the pH of the washing solution was approximately 7. It was then dried in a vacuum oven. The dried silicon powder was then sieved through a 200-mesh sieve to obtain flake silicon powder for later use. (2) The above-mentioned flake silicon powder is dispersed in a polyacrylonitrile (PAN) solution with a concentration of 8 wt% (solvent is N,N-dimethylformamide), and the surface of the silicon microspheres is uniformly coated by mechanical stirring. Then, the sample is dried to remove the solvent. The dried sample is placed in an air atmosphere and stabilized at 240°C for 1.0 h, and then carbonized at 800°C in an Ar atmosphere for 2 h to obtain a silicon-carbon composite material. The mass ratio of flake silicon powder to polyacrylonitrile (PAN) is 1:1.

[0028] Performance testing and results analysis: X-ray diffraction (XRD) analysis was performed on the raw materials (photovoltaic sample), intermediate materials (sheet silicon powder, silicon microspheres), and final product (silicon-carbon composite microspheres) used in the preparation process of Example 1. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the main diffraction peaks of the silicon-carbon composite microspheres prepared in Example 1 can all correspond to the characteristic diffraction peaks of silicon (Si). Among them, strong diffraction peaks appear at positions where 2θ equals 28.4°, 47.3°, 56.1°, 69.2° and 76.4°, indicating that the silicon core in the composite material still maintains a good crystal structure and is the main electrochemically active phase in the material. At the same time, a broadened diffraction peak appears at about 20°, which is a typical characteristic peak of carbon coating, indicating that the outer carbon layer has been successfully formed and covers the surface of the silicon microspheres.

[0029] The silicon-carbon composite microspheres prepared in Example 1 were analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that after spray drying, the original irregular sheet-like silicon powder is reconstructed into silicon microspheres with a three-dimensional interlaced stacked structure, with high sphericity and the internal sheet-like structures supporting each other, which verifies the effectiveness of the spray-forming into three-dimensional sheet-like skeleton structure described in this invention.

[0030] The materials prepared in Examples 1-2 and Comparative Examples 1-2 were used as negative electrodes, lithium sheets as positive electrodes, SA as binders, and Super P as conductive agents. Button cells were fabricated with a negative electrode material: binder: conductive agent mass ratio of 7:2:1. The prepared cells were subjected to charge-discharge performance testing. The charge-discharge performance and cycle performance are as follows: Figures 4-8 As shown.

[0031] Depend on Figure 4 It can be seen that the silicon-carbon composite material prepared in Example 1 exhibits excellent electrochemical lithium storage performance; specifically, at a current density of 100 mA·g -1 At that time, the material's initial discharge capacity was 1984.9 mAh·g. -1 The initial charge capacity is 1552.7 mAh·g. -1 This indicates that the silicon-carbon composite material can effectively utilize the high capacity properties of silicon. When the current density is increased to 500 mA·g... -1 Cyclic stability testing was conducted under the specified conditions. Figure 5 It can be seen that after 100 cycles, the material still maintains 769.3 mAh·g. -1 The discharge capacity and 762.1 mAh·g -1 The charging capacity demonstrates good cycle retention and structural stability.

[0032] Depend on Figure 5 and Figure 7 It can be seen that although the discharge specific capacity and charge specific capacity of Example 1 were lower than those of Comparative Example 1 in the first cycle, the discharge specific capacity and capacity retention rate after 100 cycles were significantly higher than those of Comparative Example 1. This indicates that although the three-dimensional cross-shaped silicon wafer skeleton constructed by spray drying can indeed alleviate silicon volume expansion, the cycling stability of the uncoated material is still insufficient due to the poor conductivity of silicon itself, the tendency of its surface to undergo continuous side reactions with the electrolyte, and the possibility of pulverization or loosening of the three-dimensional structure during cycling.

[0033] Depend on Figure 5 and Figure 8 It can be seen that although the discharge specific capacity and charge specific capacity of Example 1 were lower than those of Comparative Example 1 in the first week, the discharge specific capacity and capacity retention rate after 100 cycles were significantly higher than those of Comparative Example 1. This indicates that the photovoltaic silicon mud, due to its irregularly stacked, loosely structured flakes, and the difficulty in forming a continuous and uniform coating layer on its surface, causes uncontrolled volume expansion of silicon and repeated rupture and reconstruction of the SEI film during cycling, resulting in rapid capacity decay and poor overall electrochemical performance.

[0034] In summary, the spray-dried silicon microspheres of this invention possess a three-dimensional framework structure composed of cross-stacked sheet-like silicon particles. The internal pores effectively buffer volume expansion, while the regular surface morphology and high sphericity facilitate the formation of a continuous and dense carbon coating layer on the surface of the carbon source. This structure not only significantly alleviates the volume effect of silicon during charge and discharge but also constructs a stable electron transport network and an interface SEI film, thereby effectively improving cycle stability and capacity retention. Compared to sheet-like silicon without spherical formation, constructing a three-dimensional microsphere structure through spray drying followed by carbon coating is a key technical step in improving the cycle life and electrochemical performance of silicon-based anode materials.

[0035] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a three-dimensional cross-linked structure silicon-carbon composite material based on photovoltaic silicon slurry, characterized in that, The method comprises the following steps: S1. Waste silicon powder generated in a photovoltaic silicon mud cutting process is subjected to acid leaching with an acid leaching solution, and then is subjected to filtration, washing, drying and screening to obtain flaky silicon powder; S2. A binder is dissolved in deionized water to form a solution, a dispersing agent is added and uniformly mixed to form an aqueous slurry, and then the flaky silicon powder is added and uniformly mixed to obtain a silicon slurry; wherein the content of the flaky silicon powder in the silicon slurry is 1-10wt%; S3. The silicon slurry is subjected to spray drying treatment to obtain silicon microspheres; wherein the interior of the silicon microspheres comprises a three-dimensional support framework composed of interlaced stacking of flaky silicon; S4. The silicon microspheres are subjected to coating treatment with a carbon source, and then are sequentially subjected to stabilization treatment and carbonization treatment in an inert atmosphere to obtain a three-dimensional cross-structure silicon-carbon composite material coated with continuous carbon.

2. The method of claim 1, wherein the three-dimensional cross-linked structure silicon-carbon composite based on photovoltaic silicon sludge is prepared by the steps of: In step S1, the acid solution is any one of hydrochloric acid and hydrofluoric acid, with a concentration of 0.5-2.0 mol·L -1 , and the acid immersion time is 0.5-2 h; the sieving is performed by passing through a 200-mesh sieve, and the flaky silicon powder has a flake diameter of less than 75 μm. ​ 3. The method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud according to claim 1, characterized in that, In step S2, the binder is at least one of sodium carboxymethyl cellulose and polyvinyl alcohol, and the content is 1-10wt% of the silicon slurry; the dispersing agent is polyvinylpyrrolidone, and the content is 0.5-3wt% of the silicon slurry.

4. The method of claim 3, wherein the method further comprises the step of: In step S2, boric acid or borax also needs to be added to the aqueous slurry, and the mass ratio of the boric acid or borax to the binder is 0.05-0.

5.

5. The method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud according to claim 3, characterized in that, In step S2, urea also needs to be added to the aqueous slurry, and the content of the urea is 15-25wt% of the silicon slurry.

6. The method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud according to claim 1, characterized in that, In step S3, the inlet temperature of the spray drying treatment is 210-235℃, and the outlet temperature of the spray drying treatment is 95-100℃.

7. The method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud according to claim 1, characterized in that, In step S4, The carbon source is at least one of polyacrylonitrile, polyaniline and polyamide acid; the coating treatment comprises dispersing the silicon microspheres in a carbon source solution and uniformly mixing; the solvent in the carbon source solution is at least one of N,N-dimethylformamide and N,N-dimethylacetamide, and the content of the carbon source is 5-10wt% of the carbon source solution; the mass ratio of the silicon microspheres to the carbon source is 1:1-2; The stabilization treatment specifically comprises: 240-280℃ for 0.5-1h in an air atmosphere; The carbonization treatment in an inert atmosphere specifically comprises: 750-900℃ for 0.5-2h in a nitrogen or argon atmosphere.

8. The method for preparing a three-dimensional cross-structured silicon-carbon composite material based on photovoltaic silica mud according to claim 1, characterized in that, In step S4, the coating treatment also comprises adding 10000-mesh ultra-fine graphite powder thereto; and the mass ratio of the silicon microspheres, the carbon source and the 10000-mesh ultra-fine graphite powder is 1:1-2:

1.

9. A three-dimensional cross-linked structure silicon-carbon composite based on photovoltaic silicon slurry, characterized in that, The three-dimensional cross-structure silicon-carbon composite material prepared by the method of any one of claims 1-8 has a carbon coating layer with a thickness of 10-30nm.

10. Application of the three-dimensional cross-structure silicon-carbon composite material based on photovoltaic silicon mud according to claim 9 in a lithium ion negative electrode material.

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