Graphene-coated silicon-carbon composite material, and preparation method and application thereof

Abstract

The application relates to the technical field of preparation of lithium ion battery negative electrode materials, in particular to a graphene-coated silicon-carbon composite material and a preparation method and application thereof. The preparation method of the graphene-coated silicon-carbon composite material comprises the following steps: microwave-assisted sand milling mixing of a nano-silicon dispersion liquid, a pitch dispersion liquid, a three-block copolymer Pluronic F127 and zirconium oxide beads to obtain a mixed solution of pitch silicon particles; microwave-assisted sand milling dispersion of a sulfonated graphene dispersion liquid into the mixed solution of pitch silicon particles to obtain a slurry of sulfonated graphene-coated pitch silicon particles; and drying and heat treatment of the slurry of sulfonated graphene-coated pitch silicon particles to obtain the graphene-coated silicon-carbon composite material. The graphene prepared by the preparation method effectively buffers the volume effect generated in the lithium intercalation and deintercalation process of the silicon-based negative electrode material, so that the electrochemical performance of the material is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material preparation technology, specifically to a graphene-coated silicon-carbon composite material and its preparation method and application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, high operating voltage, low self-discharge rate, small size, light weight, and long cycle life, are widely used in portable electronic devices and electric vehicles. However, traditional silicon anode materials experience severe volume expansion and contraction during lithium insertion and extraction, leading to structural damage and degradation of electrode cycle performance, thus limiting their commercial application. To improve the cycle performance of silicon-based anode materials, current methods mainly focus on silicon particle nanosizing, silicon alloying with other metals, and silicon compositing with inert or active matrices. Among these, silicon / carbon composite anode materials have attracted considerable attention due to their excellent cycle performance and electronic conductivity. Graphene, as a two-dimensional carbon nanomaterial, possesses excellent electrical and mechanical properties, as well as a high theoretical specific surface area, demonstrating enormous application potential in the field of lithium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing graphene-coated silicon-carbon composite materials to solve the problem of insufficient electronic conductivity of silicon-based anode materials in the prior art.

[0004] The present invention also provides a graphene-coated silicon-carbon composite material to solve the problem of insufficient electronic conductivity of silicon-based anode materials in the prior art.

[0005] The present invention also provides an application of graphene-coated silicon-carbon composite material to solve the problem of poor cycle stability and electrochemical performance of silicon-based anode materials in lithium-ion batteries in the prior art.

[0006] To address the above problems, this invention proposes a method for preparing graphene-coated silicon-carbon composite materials. The technical solution adopted is as follows:

[0007] A method for preparing graphene-coated silicon-carbon composite material includes the following steps: mixing nano-silicon dispersion, pitch dispersion, triblock copolymer Pluronic F127 and zirconia beads by microwave-assisted sand milling to obtain a mixture of pitch-silicon particles.

[0008] Sulfonated graphene dispersion was added to a mixture of asphalt silica particles and dispersed by microwave-assisted sand milling to obtain a slurry of sulfonated graphene-coated asphalt silica particles.

[0009] The slurry of sulfonated graphene-coated pitch silica particles was dried and then calcined to obtain a graphene-coated silicon-carbon composite material.

[0010] The beneficial effects of this invention are:

[0011] This invention utilizes microwave-assisted milling technology to achieve uniform mixing and dispersion of asphalt silica particles in a mixture with sulfonated graphene in a sulfonated graphene dispersion, improving the uniformity and stability of the composite material. Simultaneously, by drying and calcining the slurry coated with sulfonated graphene onto asphalt silica particles, the sulfonated graphene is reduced to sulfur-doped graphene, effectively improving the electronic conductivity and cycle stability of the composite material. The graphene coating prepared by the method of this application effectively buffers the volume effect generated during the lithium insertion / extraction process of silicon-based anode materials, extending the cycle life of the material. The method of this invention is simple and easy to implement, highly practical, and the prepared composite material has advantages such as good structural stability, large reversible capacity, and designable capacity.

[0012] To further improve the electronic conductivity of graphene-coated silicon-carbon composite material, preferably, the mass ratio of nano-silicon in the nano-silicon dispersion to the mass ratio of asphalt in the asphalt dispersion is 1:(5~10).

[0013] To further improve the electronic conductivity of graphene-coated silicon-carbon composite materials and promote microwave-assisted milling, preferably, the mass ratio of nano-silicon to triblock copolymer Pluronic F127 in the nano-silicon dispersion is 10:(1~3); the mass ratio of nano-silicon to zirconia beads in the nano-silicon dispersion is 1:(20~40), and the diameter of the zirconia beads is 5~20 mm.

[0014] To further improve the uniformity and stability of the composite material, preferably, the mass ratio of nano-silicon in the mixture of asphalt silica particles to the mass ratio of sulfonated graphene in the sulfonated graphene dispersion is 1:(0.02~0.05), and the mass concentration of the sulfonated graphene dispersion is in the range of 1~5 mg / mL.

[0015] In order to fully reduce sulfonated graphene to sulfur-doped graphene and further improve the electronic conductivity and cycle stability of the composite material, preferably, the calcination temperature is 600~1000 ℃ and the time is 60~300 min.

[0016] In order to ensure uniform mixing and dispersion of materials and further improve the electronic conductivity and cycle stability of composite materials, preferably, the microwave power in the microwave-assisted sand milling mixing is 500~2500 MHz, the sand milling speed is 800~2000 rpm / min, and the sand milling time is 6~24 h.

[0017] To obtain a sufficiently dispersed nano-silicon dispersion, preferably, the preparation method of the nano-silicon dispersion includes the following steps:

[0018] Nano-silicon powder is dispersed in an organic solvent to obtain a nano-silicon dispersion; wherein the mass ratio of nano-silicon powder to organic solvent is 1:(30~60).

[0019] Preferably, the organic solvent is isopropanol.

[0020] To obtain a fully dispersed asphalt dispersion, preferably, the preparation method of the asphalt dispersion includes the following steps:

[0021] Asphalt is dispersed in an organic solvent to obtain an asphalt dispersion; wherein the mass ratio of asphalt to organic solvent is (1~2):(10~20).

[0022] Preferably, the organic solvent is isopropanol.

[0023] Preferably, the drying temperature is 60~70℃ and the drying time is 24~36h.

[0024] Preferably, the microwave power in the microwave-assisted sand milling dispersion is 500~2500 MHz, the sand milling speed is 800~2000 rpm / min, and the sand milling time is 1~4 h.

[0025] This invention also proposes a graphene-coated silicon-carbon composite material, the technical solution of which is as follows:

[0026] A graphene-coated silicon-carbon composite material is prepared by the above-described method for preparing graphene-coated silicon-carbon composite materials.

[0027] The beneficial effects of the present invention are: the graphene-coated silicon-carbon composite material of the present invention has excellent electronic conductivity and cycle stability.

[0028] The present invention also proposes a method for preparing graphene-coated silicon-carbon composite material as described above, or the application of the graphene-coated silicon-carbon composite material as described above in the negative electrode of lithium-ion batteries.

[0029] The beneficial effects of the present invention are: when the graphene-coated silicon-carbon composite material of the present invention is applied to the negative electrode of a lithium-ion battery, it effectively buffers the volume effect generated by the silicon-based negative electrode material during the lithium insertion and extraction process, prolongs the cycle life of the silicon-based negative electrode material, and improves the electrochemical performance of the silicon-based negative electrode material. Attached Figure Description

[0030] Figure 1 The XRD pattern of the graphene-coated silicon-carbon composite material obtained in Example 5 of the preparation method of the graphene-coated silicon-carbon composite material of the present invention.

[0031] Figure 2This is a SEM image of the graphene-coated silicon-carbon composite material obtained in Example 5 of the preparation method of the graphene-coated silicon-carbon composite material of the present invention.

[0032] Figure 3 The rate performance test results of the graphene-coated silicon-carbon composite material prepared in Example 5 of the preparation method of the graphene-coated silicon-carbon composite material of the present invention.

[0033] Figure 4 The AC impedance test results of the graphene-coated silicon-carbon composite material prepared in Example 5 of the preparation method of the graphene-coated silicon-carbon composite material of the present invention. Detailed Implementation

[0034] Existing silicon-based anode materials have insufficient electronic conductivity. This invention proposes a method for preparing graphene-coated silicon-carbon composite materials, comprising the following steps: mixing nano-silicon dispersion, pitch dispersion, triblock copolymer Pluronic F127, and zirconium oxide beads using microwave-assisted milling to obtain a mixture of pitch-silicon particles; adding sulfonated graphene dispersion to the mixture of pitch-silicon particles and dispersing it using microwave-assisted milling to obtain a slurry of sulfonated graphene-coated pitch-silicon particles; drying the slurry of sulfonated graphene-coated pitch-silicon particles and then heat-treating it to obtain the graphene-coated silicon-carbon composite material.

[0035] The technical concept of this invention is as follows: After mixing and dispersing nano-silicon and asphalt, a triblock copolymer, Pluronic F127, is added, followed by coating with sulfonated graphene. During subsequent calcination, Pluronic F127 decomposes to form porous carbon, H2O, and CO2. As these gases escape from the interior, they form channels connecting the inside and outside of the material. These channels facilitate the transport of lithium ions into the material, and the formed porous carbon also provides a slow-release space for the volume expansion of nano-silicon during charging and discharging. The addition of zirconia beads promotes the grinding and dispersion of nano-silicon and asphalt, crushing any potential agglomerates through a sand milling process, thus preventing the formation of large particles. Sulfonated graphene is graphene modified with sulfonic acid groups, making it easier to disperse in hydrophilic solutions. After sintering, it forms sulfur-doped graphene. The introduction of sulfur atoms can increase the carrier concentration in the electrochemical process, thereby improving ion transport. The use of sulfonated graphene as a coating in silicon-carbon anodes offers several advantages. First, it improves conductivity. Graphene itself has extremely high conductivity, and sulfonated graphene, as a derivative of graphene, also provides excellent conductivity, helping to reduce internal resistance and improve energy density and performance stability. Second, it enhances structural stability. Silicon undergoes significant volume expansion and contraction during charging and discharging, which can lead to material fracture and capacity loss. The sulfonated graphene coating effectively resists these volume changes, maintaining battery structural stability and extending battery life and cycle life. Third, it improves chemical stability. The sulfonated graphene coating enhances the chemical stability of the silicon-carbon anode material, preventing adverse reactions or oxidation with the electrolyte, thus reducing energy loss and improving battery safety. Fourth, it optimizes the solid electrolyte interphase (SEI) film. The sulfonated graphene coating also helps form a stable SEI film, further protecting the anode material and improving battery cycle stability and performance.

[0036] This invention utilizes microwave-assisted milling technology to achieve uniform mixing and dispersion of asphalt silica particles in a mixture with sulfonated graphene in a sulfonated graphene dispersion, improving the uniformity and stability of the composite material. Simultaneously, by calcining the sulfonated graphene-coated asphalt silica slurry, the sulfonated graphene is reduced to sulfur-doped graphene, effectively improving the electronic conductivity and cycle stability of the composite material. The graphene coating prepared by the method of this application effectively buffers the volume effect generated during the lithium insertion / extraction process of silicon-based anode materials, extending the cycle life of the material. The method of this invention is simple and easy to implement, highly practical, and the prepared composite material has advantages such as good structural stability, large reversible capacity, and designable capacity.

[0037] Specifically, the preparation method of graphene-coated silicon-carbon composite material includes the following steps:

[0038] 1) Add nano-silicon powder to isopropanol at a certain mass ratio, and mix and disperse it evenly by mechanical stirring to obtain nano-silicon dispersion; wherein, the mass ratio of nano-silicon powder to isopropanol is 1:(30~60); the mechanical stirring speed is 600~900 rpm / min, and the time is 1~30h;

[0039] 2) Add asphalt to isopropanol at a certain mass ratio and mix and disperse it evenly by mechanical stirring to obtain asphalt dispersion; wherein, the mass ratio of asphalt to isopropanol is (1~2):(10~20); the speed of mechanical stirring is 600~900 rpm / min and the time is 1~30h;

[0040] 3) The nano-silicon dispersion from step 1), the asphalt dispersion from step 2), a certain mass of the triblock copolymer Pluronic F127, and a certain mass of zirconia beads are sequentially added to a sand mill jar. A mixture of asphalt and silica particles is obtained by microwave-assisted sand milling. The mass ratio of nano-silicon in the nano-silicon dispersion to the mass of asphalt in the asphalt dispersion is 1:(5~10); the mass ratio of nano-silicon in the nano-silicon dispersion to the mass of the triblock copolymer Pluronic F127 is 10:(1~3); the mass ratio of nano-silicon in the nano-silicon dispersion to the mass of zirconia beads is 1:(20~40), and the diameter of the zirconia beads is 5~20 mm. The microwave power in the microwave-assisted sand mill is 500~2500 MHz, the milling speed is 800~2000 rpm / min, and the milling time is 6~24 h.

[0041] 4) A certain amount of sulfonated graphene dispersion is added to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. The mixture is further ground and dispersed by microwave-assisted sand milling technology, so that the asphalt silica particles are uniformly coated with sulfonated graphene, and a slurry of sulfonated graphene-coated asphalt silica particles is obtained. The mass ratio of nano-silicon in the asphalt silica particle mixture to the mass of sulfonated graphene in the sulfonated graphene dispersion is 1:(0.02~0.05), and the mass concentration of the sulfonated graphene dispersion is 1~5 mg / mL. The microwave power in the microwave-assisted sand milling is 500~2500 MHz, the sand milling speed is 800~2000 rpm / min, and the sand milling time is 1~4 h.

[0042] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged and dried, and then sintered in a high-temperature tube furnace using nitrogen as a protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon-carbon composite material. The calcination temperature is 600~1000 ℃ and the time is 60~300 min.

[0043] The implementation process of the present invention will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the embodiments.

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0045] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In the following examples, the raw material used, the triblock copolymer Pluronic F127, has a molecular weight of 12,600 and CAS number 9003-11-6. All other raw materials used are commercially available products that can be purchased directly or can be prepared using conventional techniques in the art.

[0047] I. Specific Embodiments of the Preparation Method of the Graphene-Coated Silicon-Carbon Composite Material of the Present Invention

[0048] Example 1

[0049] The method for preparing graphene-coated silicon-carbon composite material provided in this embodiment includes the following steps:

[0050] 1) Add 1g of nano-silicon powder to 30g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein, the mechanical stirring speed is 600 rpm / min and the time is 1h;

[0051] 2) Add 5g of asphalt to 50g of isopropanol and mix and disperse it evenly using mechanical stirring to obtain an asphalt dispersion; wherein, the mechanical stirring speed is 600rpm / min and the time is 1h;

[0052] 3) The nano-silica dispersion from step 1), the pitch dispersion from step 2), 0.1 g of Pluronic F127, and 20 g of zirconia beads with a diameter of 5 mm were sequentially added to a sand mill jar, and a mixture of pitch and silica particles was obtained by microwave-assisted sand milling technology; wherein, the microwave power in the microwave-assisted sand milling was 500 MHz, the sand milling speed was 800 rpm / min, and the sand milling time was 6 h;

[0053] 4) Add 10 mL of sulfonated graphene dispersion with a concentration of 5 mg / mL to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. Further grind and disperse using microwave-assisted sand milling technology to uniformly coat the asphalt silica particles with sulfonated graphene, and obtain a slurry of asphalt silica particles coated with sulfonated graphene. The microwave power in the microwave-assisted sand milling is 500 MHz, the sand milling speed is 800 rpm / min, and the sand milling time is 4 h.

[0054] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged to remove isopropanol, and then dried in an oven at 60 ℃ for 24 h; then sintered in a high-temperature tube furnace at 600 ℃ for 300 min with nitrogen as the protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon carbon composite material.

[0055] Example 2

[0056] The method for preparing graphene-coated silicon-carbon composite material provided in this embodiment includes the following steps:

[0057] 1) Add 1g of nano-silicon powder to 50g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein, the mechanical stirring speed is 800 rpm / min and the time is 20h;

[0058] 2) Add 6g of asphalt to 90g of isopropanol and mix and disperse it evenly using mechanical stirring to obtain an asphalt dispersion; wherein, the mechanical stirring speed is 800rpm / min and the time is 24h.

[0059] 3) The nano-silica dispersion from step 1), the pitch dispersion from step 2), 0.2 g of Pluronic F127, and 30 g of zirconia beads with a diameter of 10 mm were sequentially added to a sand mill jar. The mixture of pitch and silica particles was obtained by microwave-assisted sand milling technology. The microwave power in the microwave-assisted sand milling was 2000 MHz, the sand milling speed was 1500 rpm / min, and the sand milling time was 12 h.

[0060] 4) Add 10 mL of sulfonated graphene dispersion with a concentration of 4 mg / mL to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. Further grind and disperse using microwave-assisted sand milling technology to uniformly coat the asphalt silica particles with sulfonated graphene, and obtain a slurry of asphalt silica particles coated with sulfonated graphene. The microwave power in the microwave-assisted sand milling is 2000 MHz, the sand milling speed is 1500 rpm / min, and the sand milling time is 3h.

[0061] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged to remove isopropanol, and then dried in an oven at 60 ℃ for 36 h; then sintered in a high-temperature tube furnace at 900 ℃ for 60 min with nitrogen as the protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon carbon composite material.

[0062] Example 3

[0063] The method for preparing graphene-coated silicon-carbon composite material provided in this embodiment includes the following steps:

[0064] 1) Add 1g of nano-silicon powder to 60g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein, the mechanical stirring speed is 900 rpm / min and the time is 30h;

[0065] 2) Add 10g of asphalt to 200g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain an asphalt dispersion; wherein, the mechanical stirring speed is 900rpm / min and the time is 30h.

[0066] 3) The nano-silica dispersion from step 1), the pitch dispersion from step 2), 0.3g of Pluronic F127, and 40g of zirconia beads with a diameter of 20mm were sequentially added to a sand mill jar. The mixture of pitch and silica particles was obtained by microwave-assisted sand milling technology. The microwave power in the microwave-assisted sand milling was 2500MHz, the sand milling speed was 2000 rpm / min, and the sand milling time was 24h.

[0067] 4) Add 20 mL of sulfonated graphene dispersion with a concentration of 1 mg / mL to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. Further grind and disperse using microwave-assisted sand milling technology to uniformly coat the asphalt silica particles with sulfonated graphene, and obtain a slurry of asphalt silica particles coated with sulfonated graphene. The microwave power in the microwave-assisted sand milling is 2500 MHz, the sand milling speed is 2000 rpm / min, and the sand milling time is 1 h.

[0068] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged to remove isopropanol, and then dried in an oven at 70°C for 24 hours; then sintered in a high-temperature tube furnace at 1000°C for 180 minutes with nitrogen as the protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon-carbon composite material.

[0069] Example 4

[0070] The method for preparing graphene-coated silicon-carbon composite material provided in this embodiment includes the following steps:

[0071] 1) Add 1g of nano-silicon powder to 40g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein, the mechanical stirring speed is 750 rpm / min and the time is 10h;

[0072] 2) Add 8g of asphalt to 120g of isopropanol and mix and disperse it evenly using mechanical stirring to obtain an asphalt dispersion; wherein, the mechanical stirring speed is 750rpm / min and the time is 10h;

[0073] 3) The nano-silica dispersion from step 1), the pitch dispersion from step 2), 0.15g of Pluronic F127, and 30g of zirconia beads with a diameter of 15mm were sequentially added to a sand mill jar. The mixture of pitch and silica particles was obtained by microwave-assisted sand milling technology. The microwave power in the microwave-assisted sand milling was 1500MHz, the sand milling speed was 2000 rpm / min, and the sand milling time was 8h.

[0074] 4) Add 10 mL of sulfonated graphene dispersion with a concentration of 3 mg / mL to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. Further grind and disperse using microwave-assisted sand milling technology to uniformly coat the asphalt silica particles with sulfonated graphene, and obtain a slurry of asphalt silica particles coated with sulfonated graphene. The microwave power in the microwave-assisted sand milling is 1500 MHz, the sand milling speed is 2000 rpm / min, and the sand milling time is 2h.

[0075] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged to remove isopropanol, and then dried in an oven at 60 ℃ for 24 h; then sintered in a high-temperature tube furnace at 1000 ℃ for 60 min with nitrogen as the protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon carbon composite material.

[0076] Example 5

[0077] The method for preparing graphene-coated silicon-carbon composite material provided in this embodiment includes the following steps:

[0078] 1) Add 1g of nano-silicon powder to 60g of isopropanol and mix and disperse it evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein, the mechanical stirring speed is 800 rpm / min and the time is 20h;

[0079] 2) Add 6g of asphalt to 120g of isopropanol and mix and disperse it evenly using mechanical stirring to obtain an asphalt dispersion; wherein, the mechanical stirring speed is 800rpm / min and the time is 20h;

[0080] 3) The nano-silica dispersion from step 1), the pitch dispersion from step 2), 0.2 g of Pluronic F127, and 40 g of zirconia beads with a diameter of 5 mm were sequentially added to a sand mill jar. The mixture of pitch and silica particles was obtained by microwave-assisted sand milling technology. The microwave power in the microwave-assisted sand milling was 1800 MHz, the sand milling speed was 2000 rpm / min, and the sand milling time was 12 h.

[0081] 4) Add 15 mL of sulfonated graphene dispersion with a concentration of 3 mg / mL to the mixture in step 3), so that the asphalt silica particles are dispersed in the sulfonated graphene dispersion. Further grind and disperse using microwave-assisted sand milling technology to uniformly coat the asphalt silica particles with sulfonated graphene, and obtain a slurry of asphalt silica particles coated with sulfonated graphene. The microwave power in the microwave-assisted sand milling is 1800 MHz, the sand milling speed is 2000 rpm / min, and the sand milling time is 4 h.

[0082] 5) The slurry of sulfonated graphene-coated pitch silica particles obtained in step 4) is centrifuged to remove isopropanol, and then dried in an oven at 60 ℃ for 24 h; then sintered in a high-temperature tube furnace at 900 ℃ for 180 min with nitrogen as the protective gas. The black solid obtained by calcination is crushed and sieved to obtain graphene-coated silicon carbon composite material.

[0083] II. Experimental Examples

[0084] Experimental Example 1: XRD Characterization

[0085] The graphene-coated silicon-carbon composite material prepared in Example 5 above was characterized by XRD. Specifically, a Bruke D8 Advance XRD pattern was used to detect the prepared graphene-coated silicon-carbon composite material, and the results are as follows. Figure 1 As shown in the figure, the structure of the graphene-coated silicon-carbon composite material prepared in Example 5 is consistent with the structure of the silicon / carbon composite nanomaterial, indicating that the composite material was successfully prepared.

[0086] Experimental Example 2: SEM Characterization

[0087] The graphene-coated silicon-carbon composite material prepared in Example 5 above was characterized by SEM. Specifically, the morphology of the prepared graphene-coated silicon-carbon composite material was characterized using a ZeissSigma 300 SEM, and the results are as follows. Figure 2 As shown, the graphene-coated silicon-carbon composite material prepared in Example 5 consists of uniformly coated particles.

[0088] Experimental Example 3: Electrochemical Performance

[0089] The graphene-coated silicon-carbon composite materials prepared in Examples 1-5 were subjected to electrochemical performance testing. Specifically, the coin cell used for testing the electrochemical performance was prepared as follows: The graphene-coated silicon-carbon composite materials prepared in Examples 1-5 were used as the negative electrode material and mixed with CMC, SBR, and conductive agent (super P) in a ratio of 70:4:6:20. The mixture was then coated onto copper foil, vacuum dried, and used as the negative electrode. Lithium metal was used as the counter electrode. The electrolyte was a 1M LiPF6 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a mass ratio of 1:1. The separator was a PE / PP / PE composite membrane. The cells were assembled into CR2032 coin cells. The test conditions were: charge and discharge at a current density of 0.1~1 A / g, with the charging voltage limited to 0.01~3 V. Charge and discharge tests were conducted at different current densities, and the results are shown in Table 1.

[0090] Table 1. Discharge specific capacity of Examples 1-5 at different current densities

[0091]

[0092] As shown in Table 1, at a current density of 100 mA / g, the graphene-coated silicon-carbon composite materials prepared in Examples 1-5 exhibit the highest discharge specific capacity, exceeding 663.2 mAh / g, with a maximum of 1194.7 mAh / g. This also demonstrates that the graphene-coated silicon-carbon composite materials prepared in Examples 1-5 possess excellent electrochemical performance.

[0093] Meanwhile, the graphene-coated silicon-carbon composite material prepared in Example 5 was tested for rate performance at different current densities, and the results are as follows: Figure 3 As shown in the figure. It can be seen that the graphene-coated silicon-carbon composite material prepared in Example 5 exhibits stable charge-discharge cycling under different current densities, indicating that the material synthesized in this invention possesses good rate performance. The AC impedance test results in the frequency range of 0.01 Hz to 100 kHz are as follows. Figure 4 As shown, the radius of the semicircle in the high-frequency region of the test curve is small, indicating that the graphene-coated silicon-carbon composite material prepared in Example 5 has a small electrochemical impedance. The slope of the test curve in the low-frequency region is close to 45°, indicating that the prepared graphene-coated silicon-carbon composite material has a small diffusion resistance, that is, it has good electrochemical performance.

[0094] This demonstrates that the graphene-coated silicon-carbon composite material prepared by the method provided in this application has high electronic conductivity and cycle stability; its application in lithium batteries can significantly improve the cycle stability and electrochemical performance of lithium batteries.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing graphene-coated silicon-carbon composite material, characterized in that, Includes the following steps: The nano-silica dispersion, asphalt dispersion, triblock copolymer Pluronic F127 and zirconia beads were mixed by microwave-assisted sand milling to obtain a mixture of asphalt silica particles. Sulfonated graphene dispersion was added to a mixture of asphalt silica particles and dispersed by microwave-assisted sand milling to obtain a slurry of sulfonated graphene-coated asphalt silica particles. The slurry of sulfonated graphene-coated pitch silica particles was dried and then calcined to obtain a graphene-coated silicon-carbon composite material.

2. The method for preparing graphene-coated silicon-carbon composite material according to claim 1, characterized in that, The mass ratio of nano-silicon in the nano-silicon dispersion to the mass of asphalt in the asphalt dispersion is 1:(5~10).

3. The method for preparing graphene-coated silicon-carbon composite material according to claim 2, characterized in that, The mass ratio of nano-silicon to triblock copolymer Pluronic F127 in the nano-silicon dispersion is 10:(1~3); the mass ratio of nano-silicon to zirconia beads in the nano-silicon dispersion is 1:(20~40), and the diameter of the zirconia beads is 5~20 mm.

4. The method for preparing graphene-coated silicon-carbon composite material according to claim 3, characterized in that, The mass ratio of nano-silicon in the mixture of asphalt silica particles to the mass of sulfonated graphene in the sulfonated graphene dispersion is 1:(0.02~0.05), and the mass concentration of the sulfonated graphene dispersion is in the range of 1~5 mg / mL.

5. The method for preparing graphene-coated silicon-carbon composite material according to claim 1, characterized in that, The calcination temperature is 600~1000 ℃, and the time is 60~300 min.

6. The method for preparing graphene-coated silicon-carbon composite material according to claim 1, characterized in that, The microwave power in the microwave-assisted sand milling process is 500~2500 MHz, the milling speed is 800~2000 rpm / min, and the milling time is 6~24 h.

7. The method for preparing graphene-coated silicon-carbon composite material according to claim 1, characterized in that, The preparation method of the nano-silicon dispersion includes the following steps: Nano-silicon powder is dispersed in an organic solvent to obtain a nano-silicon dispersion; wherein the mass ratio of nano-silicon powder to organic solvent is 1:(30~60).

8. The method for preparing graphene-coated silicon-carbon composite material according to claim 1, characterized in that, The preparation method of the asphalt dispersion includes the following steps: Asphalt is dispersed in an organic solvent to obtain an asphalt dispersion; wherein the mass ratio of asphalt to organic solvent is (1~2):(10~20).

9. A graphene-coated silicon-carbon composite material, characterized in that, It is prepared by the method described in any one of claims 1 to 8 for preparing graphene-coated silicon-carbon composite materials.

10. A method for preparing a graphene-coated silicon-carbon composite material as described in any one of claims 1 to 8, or the application of the graphene-coated silicon-carbon composite material as described in claim 9 in the negative electrode of a lithium-ion battery.

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