High-pressure homogenizer-based secondary coated graphene silicon-carbon negative electrode composite material as well as preparation method and application of high-pressure homogenizer-based secondary coated graphene silicon-carbon negative electrode composite material

Abstract

The invention discloses a high-pressure homogenizer-based secondary coated graphene silicon-carbon negative electrode composite material as well as a preparation method and application thereof, and belongs to the technical field of battery materials. The preparation method comprises the following steps: firstly, carrying out carbon coating on a silicon material to form a primarily coated silicon-carbon material, then adding the primarily coated silicon-carbon material into a dispersed graphene aqueous solution, controlling the solid content of the obtained mixed solution to be 5-15wt%, carrying out secondary coating on the mixed solution through a high-pressure homogenizer provided with a cooling device, controlling the pressure of the high-pressure homogenizer to be 10-40MPa, and treating for 10-90min. The method is low in cost and easy for large-scale production, volume expansion of the silicon material can be inhibited, and cycle performance and high conductivity of the lithium ion battery can be guaranteed.

Description

Technical Field

[0001] This invention relates to the field of electrode materials, and in particular to a method for preparing and applying a secondary-coated graphene-silicon-carbon composite material. Background Technology

[0002] In recent years, the new energy industry has developed rapidly. With the increasing demand for high-energy-density lithium-ion batteries from electric vehicles and energy storage systems, replacing traditional commercial graphite with high-capacity anode materials is an inevitable trend. Silicon has a theoretical capacity of 4200 mAh g⁻¹, approximately 10 times that of graphite (372 mAh g⁻¹). It also possesses advantages such as low lithium insertion / extraction potential, abundant resources, and environmental friendliness, making it a promising candidate. However, the commercialization of silicon anode materials faces several challenges: silicon undergoes significant volume changes during lithium insertion / extraction, leading to electrode structure collapse and instability of the solid electrolyte interphase (SEI) film. Structural collapse causes silicon particles to detach from the current collector, resulting in capacity decay. Simultaneously, SEI film instability leads to increased SEI thickness and continuously increasing internal resistance. Furthermore, silicon itself has poor conductivity, resulting in slow electrochemical kinetics. Therefore, there is an urgent need to develop methods to address these issues and prepare high-performance silicon-carbon composite materials.

[0003] Chinese invention patent application CN 114005965 A discloses a graphene / carbon-coated silicon-based anode and its preparation method. This technology involves in-situ polymerization of polydopamine on the surface of a silicon-based material. Through the strong adhesive properties and hydrogen bonding of polydopamine, graphene oxide is bonded to the silicon material, achieving uniform coating of the silicon-based material by graphene. After high-temperature heat treatment, the polydopamine is carbonized, forming a layer of amorphous carbon on the surface of the silicon-based material, suppressing the volume expansion effect of the silicon-based material. The graphene oxide is then reduced to reduced graphene oxide at high temperature, improving the electronic conductivity of the material and further suppressing the volume expansion effect of the silicon-based material, thereby improving the long-term cycle performance of the lithium-ion battery. However, the main material of this technology, dopamine, is expensive, and its polymerization process requires control under specific pH values ​​(usually alkaline) and oxygen environments. The process conditions are relatively harsh, which is not conducive to large-scale production. In particular, the coating layer of this technology is formed by the intermingling of amorphous carbon formed by polydopamine carbonization and rGO reduced by polydopamine, resulting in relatively low overall conductivity, which is even lower than that of currently commercialized rGO. Summary of the Invention

[0004] In view of the existing problems of silicon materials, the purpose of this invention is to provide a low-cost, easily scalable graphene-silicon-carbon composite anode material based on a high-voltage homogenizer and its preparation method, which can suppress the volume expansion of silicon materials, ensure the cycle performance of lithium-ion batteries, and retain the high conductivity of graphene.

[0005] Another objective of this invention is to provide the application of the aforementioned graphene-silicon-carbon composite anode material based on a high-pressure homogenizer for preparing lithium-ion battery anodes.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer includes the following steps:

[0008] S1 involves mixing silicon-based materials and carbon-based materials and then calcining them at 700-900℃ under a protective atmosphere to form a silicon-carbon composite material with a core-shell structure in which carbon materials are coated on silicon-based materials in one step.

[0009] S2. Add single-layer graphene to deionized water and disperse by ultrasonic stirring to obtain a graphene solution.

[0010] The silicon-carbon composite material was added to the binder aqueous solution and dispersed to obtain a silicon-carbon composite material solution;

[0011] The graphene solution and the silicon-carbon composite material solution were mixed and stirred until homogeneous to obtain a mixed solution; the solid content of the mixed solution was controlled to be 5-15 wt%.

[0012] S3 passes the obtained mixed solution through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 10~40MPa. After the mixed solution bursts through the narrow slit of the homogenization valve of the high-pressure homogenizer, the pressure drops sharply, and the solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, achieving a secondary coating of silicon carbon particles with graphene. After cooling with cooling water in the cooling device, evaporation and drying are performed sequentially to obtain a secondary-coated graphene-silicon carbon composite material. The processing time of the high-pressure homogenizer is controlled at 10~90min; the cooling water temperature is 10-20℃.

[0013] To further achieve the objectives of this invention, preferably, the silicon-based material has a thickness of 30-50 nanometers and a wafer diameter of 500 nanometers-1.5 micrometers; the carbon-based material is one or more of phenolic resin, asphalt, and glucose; and the binder is one or two of CMC, phenolic resin, polyethylene glycol, and chitin.

[0014] Preferably, the mass ratio of the silicon-based material to the carbon-based material is 10:(1~4); the mass ratio of the single-layer graphene to the silicon-carbon composite material is (3~15):100; and the mass ratio of the binder to the single-layer graphene is (1~3):10.

[0015] Preferably, the protective atmosphere is argon or nitrogen.

[0016] Preferably, the calcination time at 700-900℃ is 1-4 hours; the heating rate to 700-900℃ is 2-5℃ / min.

[0017] Preferably, the mass ratio of monolayer graphene to deionized water in the graphene solution is 0.005-0.015:1.

[0018] Preferably, the mass ratio of the binder to water in the adhesive aqueous solution is (0.001-0.003):1; and the mass ratio of the carbon material / silicon material to the binder is 84-94:1.

[0019] Preferably, the evaporation is carried out under vacuum by rotary evaporation at a temperature of 80-100°C; the cooling water temperature in the cooling device is 10-15°C.

[0020] A graphene-silicon-carbon composite anode material based on high-pressure homogenizer secondary coating is prepared by the above preparation method; forming a silicon-carbon composite material with an amorphous carbon layer on the surface of a silicon core; and at least one silicon-carbon composite material with a graphene layer.

[0021] The application of the preparation of lithium-ion battery anodes in graphene-silicon-carbon composite anode materials based on high-pressure homogenizer secondary coating.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] 1) This invention re-coats the core-shell structured silicon-carbon material. During charging and discharging, the volume expansion of the silicon core in the core-shell structure causes the carbon shell to crack, leading to a continuous decrease in capacity. This invention uses graphene for secondary coating. Due to the high strength of graphene, the secondary coating can inhibit the carbon shell from being stretched open, and at the same time prevent silicon particles escaping from the core-shell structure from being exposed, effectively avoiding the risk of expansion rate.

[0024] 2) Moreover, the high conductivity of the graphene with secondary coating in this invention compensates for the poor conductivity of silicon materials, improves the diffusion rate of lithium ions in the material, and improves the electrochemical performance and efficiency of the material.

[0025] 3) The secondary coating of this invention can be achieved simply by using a high-pressure homogenizer equipped with a cooling device. It is only necessary to control the pressure and time of the high-pressure homogenizer and the temperature of the cooling water. No calcination is required. The process is simple, low-cost, and easy to scale up.

[0026] 4) The silicon-carbon composite anode material obtained by this invention can suppress the volume expansion of silicon materials, ensure the cycle performance of lithium-ion batteries, and retain the high conductivity of graphene, with obvious comprehensive performance advantages.

[0027] 5) This invention fully utilizes the excellent mechanical properties of graphene, further ensuring that the expansion rate is within a small range when the material is applied, and also significantly reduces the escape of silicon particles due to the core-shell structure rupture during cycling, thus ensuring good cycling performance of the material. Attached Figure Description

[0028] Figure 1 This is a SEM image of the secondary-coated graphene-silicon-carbon composite material prepared in Example 1 of this invention.

[0029] Figure 2 This is a TEM image of the secondary-coated graphene-silicon-carbon composite material prepared in Example 1 of this invention.

[0030] Figure 3 This is a Raman diagram of the secondary-coated graphene-silicon-carbon composite material prepared in Example 1 of this invention.

[0031] Figure 4 This is a 2A 400-cycle diagram of the secondary-coated graphene-silicon-carbon composite material prepared in Example 1 of this invention. Detailed Implementation

[0032] To better understand the present invention, it will be further described below with reference to the accompanying drawings and specific embodiments. However, the implementation of the present invention is not limited thereto. The described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Regarding the graphene / carbon-coated silicon-based material prepared in Chinese invention patent application CN 114005965 A, its structure is a single-layer core-shell composite formed by polydopamine and graphene oxide co-coating silicon carbon particles. Since the coating layer is formed by the mutual doping of amorphous carbon formed by polydopamine carbonization and rGO reduced by polydopamine, the overall conductivity is still lower than that of commercially available rGO. Moreover, dopamine raw materials are expensive and the preparation process is complex, which is not conducive to large-scale production.

[0034] This invention achieves secondary coating using a high-pressure homogenizer equipped with a cooling device. The secondary coating process can be completed simply by controlling the pressure and time of the high-pressure homogenizer and the temperature of the cooling water. This effectively overcomes the drawback of Chinese invention patent application CN114005965 A, which requires the use of expensive dopamine raw materials. Furthermore, the process is simple and suitable for large-scale production. More importantly, the invention obtains a silicon-carbon composite material with a core-shell structure coated with graphene sheets, forming a composite material with a double-layer coating structure. Specifically, the silicon core surface is coated with an amorphous carbon layer; the graphene layer coats at least one silicon-carbon composite material. In contrast, this invention directly uses a single layer of graphene to physically coat the silicon-carbon material, thus retaining the high conductivity of graphene and significantly improving the material's kinetic properties.

[0035] The high-pressure homogenizer used in this invention differs from existing technologies. For example, Chinese invention patent application CN111370665A discloses a method for preparing a high-specific-capacity multi-layered stacked silicon-carbon composite material. This material is obtained by sintering and CVD coating of a multi-layered stacked silicon-carbon composite material precursor. The precursor is formed by electrostatic self-assembly of nano-silicon and modified graphene. The nano-silicon is uniformly distributed on the graphene sheets. The modified graphene is obtained by surface modification after mixing graphene and cationic additives. The graphene itself is prepared using a high-pressure homogenizer and exhibits high crystallinity and a few-layered sheet structure. This technology prepares graphene from graphite using a high-pressure homogenizer. Specifically, under high pressure, the graphite slurry is forced through the tiny gaps of a homogenizing valve, generating extremely high laminar shear force. This shear force acts on the interlayer of graphite particles, and its strength is sufficient to overcome the van der Waals forces between layers, peeling the graphite sheets layer by layer to finally obtain few-layered graphene.

[0036] This invention controls the solid content of the mixed solution to be 5-15 wt%, the pressure of the high-pressure homogenizer to be 10-40 MPa, and the processing time to be 10-90 min. The mixed solution of graphene and silicon-carbon composite material is ejected through the homogenization valve of the high-pressure homogenizer, creating a cavitation effect. As the slurry bursts through the slit, the pressure drops sharply, causing the solvent to vaporize and form microbubbles, which then collapse instantly. This bubble collapse generates extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. Simultaneously, the cavitation effect leads to collisions between graphene and silicon-carbon particles, with the graphene bending along the surface of the silicon-carbon particles, achieving graphene encapsulation of the silicon-carbon particles. The graphene sheet size is much larger than the silicon-carbon particles; a single graphene sheet can encapsulate multiple particles. The pressure of the high-pressure homogenizer determines the energy source of the hydrodynamic effect, directly determining the intensity of the shear force and cavitation effect. By controlling the pressure, the integrity of the material is ensured while achieving uniform encapsulation. The high-pressure homogenization time ensures the number of times the mixed solution circulates within the homogenization chamber, guaranteeing a thorough and uniform coating reaction. The solid content of the mixed solution determines the viscosity of the working fluid and the average distance between particles, directly affecting the coating efficiency. A cooling device promptly removes heat generated by high pressure and vigorous fluid action, preventing localized overheating from damaging the structure of graphene and silicon-carbon materials, thus ensuring stable product performance and high capacity retention.

[0037] Based on the above mechanism, the present invention provides a method for preparing a graphene-silicon-carbon composite anode material with secondary coating using a high-voltage homogenizer, comprising the following steps:

[0038] S1 involves mixing silicon-based materials and carbon-based materials and then calcining them at 700-900℃ under a protective atmosphere to form a silicon-carbon composite material with a core-shell structure in which carbon materials are coated on silicon-based materials in one step.

[0039] S2. Add single-layer graphene to deionized water and disperse by ultrasonic stirring to obtain a graphene solution.

[0040] The silicon-carbon composite material was added to the binder aqueous solution and dispersed to obtain a silicon-carbon composite material solution;

[0041] The graphene solution and the silicon-carbon composite material solution were mixed and stirred until homogeneous to obtain a mixed solution; the solid content of the mixed solution was controlled to be 5-15 wt%.

[0042] S3 passes the obtained mixed solution through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 10~40MPa. After the mixed solution bursts through the narrow slit of the homogenization valve of the high-pressure homogenizer, the pressure drops sharply, and the solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, achieving a secondary coating of silicon carbon particles with graphene. After cooling with cooling water in the cooling device, evaporation and drying are performed sequentially to obtain a secondary-coated graphene-silicon carbon composite material. The processing time of the high-pressure homogenizer is controlled at 10~90min; the cooling water temperature is 10-20℃.

[0043] The method of this invention involves a single coating process, similar to existing techniques. Both the silicon-based and carbon-based materials used are existing materials. Preferably, the silicon-based material is a silicon wafer with a thickness of 30-50 nanometers and a diameter of 500 nanometers to 1.5 micrometers. The carbon-based material is preferably one or more of phenolic resin, asphalt, and glucose. Similar techniques have also disclosed the dosages, with a preferred mass ratio of silicon-based to carbon-based material of 10:(1-4). The calcination process is common, with a preferred calcination time of 1-4 hours at 700-900°C. The preferred heating rate to 700-900°C is 2-5°C / min. The protective atmosphere is conventional in the art, such as argon or nitrogen.

[0044] In this invention, the graphene solution and the silicon-carbon composite material solution are mixed and stirred evenly to obtain a mixed solution. It is important to control the solid content of the mixed solution to be 5-15 wt%. Controlling the solid content affects the effectiveness of the secondary coating. The mixing of the graphene solution and the silicon-carbon composite material solution is a conventional practice. The binder is selected from one or two of CMC, phenolic resin, polyethylene glycol, and chitin. The preferred mass ratio of monolayer graphene to silicon-carbon composite material is (3-15):100; the preferred mass ratio of binder to monolayer graphene is (1-3):10. The preferred mass ratio of monolayer graphene to deionized water in the graphene solution is 0.005-0.015:1. The preferred mass ratio of binder to water in the binder aqueous solution is (0.001-0.003):1; the preferred mass ratio of carbon material / silicon material to binder is 84-94:1.

[0045] In the method of the present invention, evaporation is preferably carried out under vacuum by rotary evaporation, and the evaporation temperature is preferably 80~100℃; the cooling water temperature in the cooling device of the high-pressure homogenizer is preferably 10-20℃.

[0046] The silicon-carbon composite material with secondary graphene coating obtained in this invention has silicon as the core; an amorphous carbon layer coating the surface of the silicon core constitutes the primary coating layer; and a graphene layer wrapped around the primary coating layer by high-pressure homogenization force constitutes the flexible secondary coating layer, forming a conductive layer. The carbon shell can suppress the volume expansion of the silicon nanosheets, while the carbon material can compensate for the poor conductivity of silicon. The secondary coating of graphene, through the excellent conductivity of graphene, can improve the conductivity and ion diffusion rate of the material. The method of this invention ensures the integrity and non-damage of graphene, fully utilizes the good mechanical properties of graphene, further ensures that the expansion rate is within a small range during material application, and also significantly reduces the escape of silicon particles due to core-shell structure breakage during cycling.

[0047] Example 1

[0048] A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer includes the following steps:

[0049] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 4:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours to obtain a one-time coated silicon-carbon composite material.

[0050] (S2) 30g of graphene was added to 1.5L of deionized water and sonicated for 0.5 h, then stirred for 1 h to disperse it, to obtain a graphene solution; 270g of the obtained one-time coated silicon-carbon composite material was added to 1.5L of 1wt% phenolic resin solution and stirred for 1 h to obtain a silicon-carbon composite material phenolic resin solution; the obtained graphene solution and silicon-carbon composite material phenolic resin solution were mixed and stirred for 2 h to obtain a mixed solution with a solid content of 9wt%.

[0051] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 15 MPa. After the mixed solution bursts through the narrow slit of the homogenizing valve of the high-pressure homogenizer, the pressure drops sharply. The solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, realizing the secondary coating of silicon carbon particles by graphene. The processing time of the high-pressure homogenizer is controlled at 80 min. The secondary coating material is cooled by the cooling water in the cooling device at a temperature of 15°C. After the processing is completed, it is subjected to rotary evaporation at 100°C and then dried overnight to obtain the secondary coated graphene silicon carbon composite material.

[0052] Figure 1This is a SEM image of the secondary-coated graphene-silicon-carbon composite material prepared in Example 1. The rough-surfaced particles in the image are the primary-coated silicon-carbon particles (Si / C particles), while the smooth-surfaced areas are where the silicon-carbon particles are covered by a thin film (graphene layer). Over 90% of the particles are covered by a continuous thin film. The wrinkled film structure shown in the image corresponds in morphology and size to the single-layer graphene that plays a crucial coating role in this material. Figure 2 As shown, the TEM image clearly reveals the core-shell structure of the prepared material, with a high-contrast silicon core at the center surrounded by an amorphous carbon layer. The image also clearly shows a transparent, wrinkled graphene film encapsulating multiple core-shell particles. These results demonstrate that graphene-coated core-shell particles were successfully achieved using a high-pressure homogenizer.

[0053] Figure 3 The images show the Raman spectra of the graphene-coated silicon-carbon composite material prepared in Example 1 and the uncoated silicon-carbon material prepared in Comparative Example 1. The peak at 510 cm⁻¹ corresponds to the characteristic peak of Si. ID / IG represents the intensity ratio of the D peak (approximately 1350 cm⁻¹) to the G peak (1580 cm⁻¹), used to characterize the degree of structural defects in carbon materials. After being coated with rGO, the relative intensity of the characteristic peak of Si is significantly weakened, while ID / IG increases, indicating that rGO was successfully introduced and that rGO folds and coats the Si / C particles.

[0054] Example 2

[0055] A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer includes the following steps:

[0056] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 3:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 800℃ at a rate of 4℃ / min and held for 3h to obtain a one-time coated silicon-carbon composite material.

[0057] (S2) Add 30g of graphene to 1.5L of deionized water and sonicate for 0.5 h, then stir for 1 h to disperse; add 270g of the above silicon carbon material to 1.5L of 1wt% polyethylene glycol solution and stir for 1 h. Finally, mix the two solutions and stir for 2 h to obtain a mixed solution with a solid content of 9wt%.

[0058] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 25 MPa. After the mixed solution bursts through the narrow slit of the homogenizing valve of the high-pressure homogenizer, the pressure drops sharply. The solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, realizing the secondary coating of silicon carbon particles by graphene. The processing time of the high-pressure homogenizer is controlled at 70 min. The secondary coating material is cooled in the cooling water of the cooling device at a temperature of 15°C. After the processing is completed, it is subjected to rotary evaporation at 100°C and then dried overnight to obtain the secondary coated graphene silicon carbon composite material.

[0059] Example 3

[0060] A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer includes the following steps:

[0061] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 5:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 700℃ at a rate of 2℃ / min and held for 4 hours to obtain a one-time coated silicon-carbon composite material.

[0062] (S2) Add 30g of graphene to 1.5L of deionized water and sonicate for 0.5 h, then stir for 1 h to disperse; add 270g of the above silicon carbon material to 1.5L of a mixed aqueous solution of 0.5wt% CMC and 0.5wt% phenolic resin and stir for 1 h. Finally, mix the two solutions and stir for 2 h to obtain a mixed solution with a solid content of 9wt%.

[0063] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 35 MPa. After the mixed solution bursts through the narrow slit of the homogenizing valve of the high-pressure homogenizer, the pressure drops sharply. The solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, realizing the secondary coating of silicon carbon particles by graphene. The processing time of the high-pressure homogenizer is controlled at 60 min. The secondary coating material is cooled in the cooling water of the cooling device at a temperature of 15°C. After the treatment is completed, it is subjected to rotary evaporation at 100°C and then dried overnight to obtain the secondary coated graphene silicon carbon composite material.

[0064] Example 4

[0065] A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer includes the following steps:

[0066] (S1) The nano-silicon wafers and asphalt were mixed at a mass ratio of 4:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours to obtain a one-time coated silicon-carbon composite material.

[0067] (S2) Add 45g of graphene to 1.5L of deionized water and sonicate for 0.5 h, then stir for 1 h to disperse; add 270g of the above silicon carbon material to 1.5L of 1wt% phenolic resin solution and stir for 1 h. Finally, mix the two solutions and stir for 2 h to obtain a mixed solution with a solid content of 9.5wt%.

[0068] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 15 MPa. After the mixed solution bursts through the narrow slit of the homogenizing valve of the high-pressure homogenizer, the pressure drops sharply. The solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, realizing the secondary coating of silicon carbon particles by graphene. The processing time of the high-pressure homogenizer is controlled at 80 min. The secondary coating material is cooled in the cooling water of the cooling device at a temperature of 15°C. After the processing is completed, it is subjected to rotary evaporation at 100°C and then dried overnight to obtain the secondary coated graphene silicon carbon composite material.

[0069] Comparative Example 1

[0070] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 4:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours to obtain a one-time coated silicon-carbon composite material.

[0071] (S2) Add 0g of graphene to 1.5L of deionized water and sonicate for 0.5h, then stir for 1h to disperse; add 270g of the above silicon-carbon composite material to 1.5L of 1wt% phenolic resin solution and stir for 1h. Finally, mix the two solutions and stir for 2h to obtain a mixed solution with a solid content of 8.2wt%.

[0072] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 15 MPa; the processing time is 80 min; the cooling water temperature is 15 °C. After the processing is completed, rotary evaporation is carried out at 100 °C, and then the solution is dried overnight to obtain silicon-carbon composite material.

[0073] Comparative Example 2

[0074] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 4:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours to obtain a one-time coated silicon-carbon composite material.

[0075] (S2) Add 30g of graphene to 1.5L of deionized water and sonicate for 0.5h, then stir for 1h to disperse; add 270g of the above-mentioned one-time coated silicon-carbon composite material to 1.5L of 1wt% phenolic resin solution and stir for 1h; finally, mix the two solutions and stir for 2h to obtain a mixed solution.

[0076] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 50 MPa; the processing time is 80 min; the cooling water temperature is 15℃; after the processing is completed, it is rotary evaporated at 100℃ and then dried overnight to obtain a secondary coated graphene silicon carbon composite material.

[0077] Comparative Example 3

[0078] (S1) The nano-silicon wafers and phenolic resin were mixed at a mass ratio of 4:1, and then transferred to a box furnace. Argon gas was introduced for calcination. The temperature was increased to 900℃ at a rate of 5℃ / min and held for 2 hours to obtain a one-time coated silicon-carbon composite material.

[0079] (S2) Add 30g of graphene to 0.6L of deionized water and sonicate for 0.5 h, then stir for 1 h to disperse; add 270g of the above silicon-carbon composite material to 0.6L of 1% phenolic resin solution and stir for 1 h. Finally, mix the two solutions and stir for 2 h to obtain a mixed solution with a solid content of 20wt%.

[0080] (S3) The obtained mixed solution is passed through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 15 MPa; the processing time is 80 min; the cooling water temperature is 15℃; after the processing is completed, it is rotary evaporated at 100℃ and then dried overnight to obtain a secondary coated graphene silicon carbon composite material.

[0081] Comparative Example 4

[0082] Chinese invention patent application CN111370665A discloses a high-specific-capacity multi-layered stacked silicon-carbon composite material. The preparation method is as follows:

[0083] (S1) Weigh 100 parts of graphite, mix the graphite and deionized water evenly and add them to a high-pressure homogenizer. Set the pressure of the high-pressure homogenizer to 1200 bar and cycle 50 times to convert the graphite glass into sheet-like graphene and obtain graphene slurry.

[0084] (S2) Weigh 30 parts of polyvinylpyrrolidone, add it to the graphene slurry obtained in S1 and stir evenly to obtain the modified graphene slurry.

[0085] (S3) Weigh 30 parts of nano-silicon powder and add it to the modified graphene slurry obtained in S2 and mix evenly to obtain a graphene and nano-silicon mixed slurry.

[0086] (S4) The graphene and nano-silicon mixed slurry obtained in S3 is spray-dried at an air inlet temperature of 170°C to obtain a multi-layer stacked silicon-carbon composite material precursor.

[0087] (S5) The multi-layer stacked silicon-carbon composite material precursor obtained in S4 was sintered in nitrogen to obtain a sample. The sintering temperature was 700℃ and the sintering time was 40min.

[0088] (S6) The sample obtained in S5 was subjected to CVD coating under acetylene gas conditions at a coating temperature of 750℃ for 20 min.

[0089] Application Examples

[0090] The silicon-carbon materials prepared in the above examples and comparative examples were used as negative electrode materials to assemble lithium-ion batteries. Taking CR2032 coin cell as an example, electrochemical tests were conducted at room temperature (25°C). The test method was as follows: The silicon-carbon materials prepared in Examples 1-4 and Comparative Examples 1-3 were used as negative electrode materials and prepared into a slurry with a ratio (active material: Super P: PAA-Li = 70:15:15, where PAA is a 4% aqueous solution). The slurry was then coated onto copper foil and vacuum dried for 12 hours. After drying, the slurry was pressed into a sheet to obtain a negative electrode sheet. The thickness X of the negative electrode sheet was recorded. The electrolyte used was 1.0 M LiPF6. 6， The solvent was a mixed solution of EC, DEC, DMC, and FEC in a mass ratio of 26.96:19.78:21.70:22.26. The separator was a PP film, and the positive electrode was a lithium sheet. Constant current charge-discharge was performed using a Neware battery testing system, with the charge-discharge voltage limited to 0.005V-2V. Data acquisition and control were performed using a computer-controlled charge-discharge cabinet. The battery underwent five cycles. After testing, the completed battery was disassembled, and the thickness Y of the negative electrode was measured. The electrode expansion rate was calculated as (Y - X) / X × 100%. The electrochemical test results of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1 and... Figure 4 As shown.

[0091] Table 1. Test results of negative electrode performance in the examples and comparative examples. ;

[0092] Table 1 shows that the materials in Examples 1-4 exhibit a capacity retention of >82% and an expansion rate of <45% after 400 cycles at a current of 2.0A. In comparison, the silicon-carbon anode material prepared in Chinese invention patent application CN120978054 A has a capacity retention of >82% after 100 cycles, and the silicon-carbon anode material prepared in Chinese invention patent application CN120967319 A has an electrode expansion rate of approximately 70%. This demonstrates that the secondary-coated graphene-silicon-carbon composite material prepared in this invention possesses high capacity and high cycle stability compared to existing silicon-carbon anode materials. The main reason is that the graphene sheets in this invention encapsulate the silicon-carbon particles, preventing direct contact between silicon and the electrolyte and reducing side reactions. The secondary coating of silicon-carbon particles with graphene further suppresses the volume expansion of silicon, resulting in excellent cycle performance.

[0093] The capacity retention and expansion rate of Comparative Example 1 were significantly worse, mainly because graphene coating was not used. The volume expansion of silicon material during cycling could not be effectively suppressed, and more silicon surface was exposed to the electrolyte, leading to an aggravation of side reactions.

[0094] The cycle performance of Comparative Example 2 was only 73.32%, significantly lower than 80%, and the expansion rate reached 70%. This was mainly because the homogenization pressure of the high-pressure homogenizer was too high (50 MPa), which caused the graphene to be continuously broken down during the coating process, ultimately resulting in smaller graphene particles and a poorer coating effect.

[0095] The cycling performance and rate performance of Comparative Example 3 were very poor, mainly because the high solid content of the mixed solution led to a sharp increase in solution viscosity, poor fluidity, and too small particle spacing. Ultimately, the graphene and silicon carbon particles collided and ground violently with each other during the coating process, destroying the original structure of the silicon carbon particles and graphene.

[0096] The capacity and capacity retention of Comparative Example 4 are worse than those of Examples 1-4, according to CN111370665A. Figure 3 In its multi-layered stacked silicon-carbon composite material, silicon particles are mainly attached to the graphene surface, forming a dispersed structure with graphene as the carrier. The present invention, however... Figure 2As shown, the structure is significantly different from Comparative Example 4, exhibiting a complete coating of silicon-carbon particles by graphene sheets. In the multi-layer stacked structure, some silicon particles are directly stacked, preventing sufficient contact with graphene and resulting in insufficient conductivity, thus hindering the effective utilization of the silicon material's capacity. Simultaneously, the silicon particles are partially exposed, making them prone to detachment and structural damage during the dramatic volume expansion during charge and discharge, ultimately leading to poor cycle performance. In contrast, the secondary-coated graphene-silicon-carbon composite material prepared in this invention completely encapsulates the silicon-carbon particles with graphene sheets. This ensures sufficient contact between the silicon-carbon particles and graphene, constructing a continuous and efficient conductive network. Furthermore, graphene inhibits the volume expansion of silicon-carbon particles during charge and discharge, preventing the detachment of active materials, thereby significantly improving the material's cycle stability and structural integrity.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer, characterized in that... Includes the following steps: S1 involves mixing silicon-based materials and carbon-based materials and then calcining them at 700-900℃ under a protective atmosphere to form a silicon-carbon composite material with a core-shell structure in which carbon materials are coated on silicon-based materials in one step. S2. Add single-layer graphene to deionized water and disperse by ultrasonic stirring to obtain a graphene solution. The silicon-carbon composite material was added to the binder aqueous solution and dispersed to obtain a silicon-carbon composite material solution; The graphene solution and the silicon-carbon composite material solution were mixed and stirred until homogeneous to obtain a mixed solution; the solid content of the mixed solution was controlled to be 5-15 wt%. S3 passes the obtained mixed solution through a high-pressure homogenizer equipped with a cooling device. The pressure of the high-pressure homogenizer is controlled at 10~40MPa. After the mixed solution bursts through the narrow slit of the homogenization valve of the high-pressure homogenizer, the pressure drops sharply, and the solvent in the mixed solution vaporizes to form microbubbles. The bubbles collapse instantly, generating extremely strong asymmetric, random local shock waves and microjets, causing the graphene in the mixed solution to bend, curl, and wrinkle. At the same time, after the mixed solution bursts through the slit, the graphene and silicon carbon particles collide with each other, and the graphene bends along the surface of the silicon carbon particles, achieving a secondary coating of silicon carbon particles with graphene. After cooling with cooling water in the cooling device, evaporation and drying are performed sequentially to obtain a secondary-coated graphene-silicon carbon composite material. The processing time of the high-pressure homogenizer is controlled at 10~90min; the cooling water temperature is 10-20℃.

2. The method for preparing graphene-silicon-carbon composite anode material based on secondary coating using a high-pressure homogenizer according to claim 1, wherein the silicon-based material has a thickness of 30-50 nanometers and a wafer diameter of 500 nanometers-1.5 micrometers; the carbon-based material is one or more of phenolic resin, asphalt, and glucose; and the binder is one or two of CMC, phenolic resin, polyethylene glycol, and chitin.

3. The preparation method of graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The mass ratio of silicon-based material to carbon-based material is 10:(1~4); the mass ratio of single-layer graphene to silicon-carbon composite material is (3~15):100; and the mass ratio of binder to single-layer graphene is (1~3):

10.

4. The preparation method of graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The protective atmosphere is argon or nitrogen.

5. The preparation method of graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The calcination time at 700-900℃ is 1-4 hours; the heating rate to 700-900℃ is 2-5℃ / min.

6. The preparation method of the graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The mass ratio of monolayer graphene to deionized water in the graphene solution is 0.005-0.015:

1.

7. The preparation method of graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The mass ratio of the binder to water in the adhesive aqueous solution is (0.001-0.003):1; the mass ratio of the carbon material / silicon material to the binder is 84-94:

1.

8. The preparation method of graphene-silicon-carbon composite anode material based on secondary coating using a high-voltage homogenizer according to claim 1, characterized in that, The evaporation is carried out under vacuum by rotary evaporation at a temperature of 80-100°C; the cooling water temperature in the cooling device is 10-15°C.

9. A graphene-silicon-carbon composite anode material based on secondary coating using a high-pressure homogenizer, characterized in that... It is prepared by the preparation method according to any one of claims 1-8; forming a silicon-carbon composite material with an amorphous carbon layer covering the surface of a silicon core; and having at least one silicon-carbon composite material coated with a graphene layer.

10. The application of the graphene-silicon-carbon composite anode material based on high-pressure homogenizer secondary coating as described in claim 9 in the preparation of lithium-ion battery anodes.

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