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

Abstract

The invention relates to the technical field of preparation of lithium ion battery negative electrode materials, in particular to a graphene-coated silicon-carbon composite material as well as a preparation method and application thereof. The preparation method of the graphene-coated silicon-carbon composite material comprises the following steps: carrying out microwave-assisted sanding mixing on a nano silicon dispersion liquid, an asphalt dispersion liquid, a triblock copolymer Pluronic F127 and zirconium oxide beads to obtain a mixed liquid of asphalt silicon particles; adding the sulfonated graphene dispersion liquid into the mixed liquid of asphalt silicon particles, and carrying out microwave-assisted sanding dispersion to obtain slurry of sulfonated graphene coated asphalt silicon particles; and drying the slurry of the sulfonated graphene coated asphalt silicon particles, and carrying out heat treatment to obtain the graphene coated silicon-carbon composite material. The graphene coating prepared by the preparation method provided by the invention effectively buffers the volume effect of the silicon-based negative electrode material generated in the lithium intercalation and deintercalation process, so that the electrochemical performance of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of negative electrode materials for lithium-ion batteries, and in particular to a graphene-coated silicon-carbon composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their high energy density, high operating voltage, low self-discharge rate, small size, light weight and long cycle life. However, traditional silicon negative electrode materials will produce severe volume expansion and contraction during the insertion and extraction of lithium, resulting in the destruction of the material structure and the decline of the electrode cycle performance, which limits its commercial application. In order to improve the cycle performance of silicon-based negative electrode materials, the current main approaches to improve them are silicon particle nano-sizing, silicon alloying with other metals, and silicon composite with inert or active matrices. Among them, silicon / carbon composite negative electrode materials have attracted much attention due to their good cycle performance and electronic conductivity. Graphene, as a two-dimensional carbon nanomaterial, has excellent electrical and mechanical properties and a high theoretical specific surface area, and shows great application potential in the field of lithium-ion batteries. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a graphene-coated silicon-carbon composite material to solve the problem of insufficient electronic conductivity of silicon-based negative electrode 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 negative electrode materials in the prior art.

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

[0006] In order to solve the above problems, the present invention proposes a method for preparing a graphene-coated silicon-carbon composite material, and the technical solution adopted is: A method for preparing a graphene-coated silicon-carbon composite material comprises the following steps: mixing a nano-silicon dispersion, an asphalt dispersion, a triblock copolymer Pluronic F127 and zirconium oxide beads by microwave-assisted sand milling to obtain a mixed solution of asphalt silicon particles; The sulfonated graphene dispersion is added to the mixed solution of asphalt silicon particles for microwave-assisted sand milling dispersion to obtain a slurry of sulfonated graphene-coated asphalt silicon particles; The slurry of sulfonated graphene-coated asphalt silicon particles is dried and then calcined to obtain a graphene-coated silicon-carbon composite material.

[0007] The beneficial effects of the present invention are: The present invention utilizes microwave-assisted sand milling technology to achieve uniform mixing and dispersion of asphalt silicon particles in a mixed solution of asphalt silicon particles and sulfonated graphene in a sulfonated graphene dispersion, thereby improving the uniformity and stability of the composite material; at the same time, by drying the slurry of sulfonated graphene-coated asphalt silicon particles and calcining it, the sulfonated graphene is reduced to sulfur-doped graphene, thereby effectively improving the electronic conductivity and cycle stability of the composite material. The coating of graphene prepared by the preparation method of the present application effectively buffers the volume effect generated by the silicon-based negative electrode material during the lithium insertion and extraction process, thereby extending the cycle life of the material. The method of the present invention is simple and easy to implement, has a high degree of practicality, and the prepared composite material has the advantages of good structural stability, large reversible capacity, and designable capacity.

[0008] In order to further improve the electronic conductivity of the graphene-coated silicon-carbon composite material, preferably, the mass ratio of the nano-silicon in the nano-silicon dispersion to the mass ratio of the asphalt in the asphalt dispersion is 1:(5-10).

[0009] In order to further improve the electronic conductivity of the graphene-coated silicon-carbon composite material and promote microwave-assisted sand grinding, preferably, the mass ratio of the nano-silicon in the nano-silicon dispersion to the triblock copolymer Pluronic F127 is 10:(1~3); the mass ratio of the nano-silicon in the nano-silicon dispersion to the zirconia beads is 1:(20~40), and the diameter of the zirconia beads is 5~20 mm.

[0010] In order to further improve the uniformity and stability of the composite material, preferably, the mass ratio of nano-silicon in the mixed solution of asphalt silicon particles to the mass ratio of sulfonated graphene in the sulfonated graphene dispersion is 1:(0.02~0.05), and the mass concentration range of the sulfonated graphene dispersion is 1~5 mg / mL.

[0011] In order to fully reduce the 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° C. and the time is 60-300 min.

[0012] In order to make the materials evenly mixed and dispersed and further improve the electronic conductivity and cycle stability of the composite material, 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.

[0013] In order to obtain a fully dispersed nano-silicon dispersion, preferably, the preparation method of the nano-silicon dispersion comprises the following steps: The nano-silicon powder is dispersed in an organic solvent to obtain a nano-silicon dispersion; wherein the mass ratio of the nano-silicon powder to the organic solvent is 1:(30-60).

[0014] Preferably, the organic solvent is isopropanol.

[0015] In order to obtain a fully dispersed asphalt dispersion, preferably, the preparation method of the asphalt dispersion comprises the following steps: The asphalt is dispersed in an organic solvent to obtain an asphalt dispersion; wherein the mass ratio of the asphalt to the organic solvent is (1~2):(10~20).

[0016] Preferably, the organic solvent is isopropanol.

[0017] Preferably, the drying temperature is 60-70° C. and the drying time is 24-36 hours.

[0018] Preferably, in microwave-assisted sand milling dispersion, the microwave power is 500-2500 MHz, the sand milling speed is 800-2000 rpm / min, and the sand milling time is 1-4 h.

[0019] The present invention also proposes a graphene-coated silicon-carbon composite material, and the technical solution adopted is: A graphene-coated silicon-carbon composite material is prepared by the above-mentioned method for preparing the graphene-coated silicon-carbon composite material.

[0020] 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.

[0021] The present invention also proposes a method for preparing the above-mentioned graphene-coated silicon-carbon composite material to prepare the graphene-coated silicon-carbon composite material or the application of the above-mentioned graphene-coated silicon-carbon composite material in the negative electrode of a lithium-ion battery.

[0022] The beneficial effects of the present invention are as follows: the graphene-coated silicon-carbon composite material of the present invention is applied in the negative electrode of a lithium-ion battery, which 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The XRD spectrum of the graphene-coated silicon-carbon composite material obtained in Example 5 of the method for preparing the graphene-coated silicon-carbon composite material of the present invention; Figure 2 This is a SEM image of the graphene-coated silicon-carbon composite material obtained in Example 5 of the method for preparing the graphene-coated silicon-carbon composite material of the present invention; Figure 3 The rate performance test result of the graphene-coated silicon-carbon composite material prepared in Example 5 of the method for preparing the graphene-coated silicon-carbon composite material of the present invention; Figure 4 This is the AC impedance test result of the graphene-coated silicon-carbon composite material prepared in Example 5 of the method for preparing the graphene-coated silicon-carbon composite material of the present invention. DETAILED DESCRIPTION

[0024] The electronic conductivity of silicon-based negative electrode materials in the prior art is insufficient. The present invention provides a method for preparing a graphene-coated silicon-carbon composite material, comprising the following steps: mixing a nano-silicon dispersion, an asphalt dispersion, a triblock copolymer Pluronic F127 and zirconium oxide beads by microwave-assisted sand milling to obtain a mixed solution of asphalt silicon particles; adding a sulfonated graphene dispersion to the mixed solution of asphalt silicon particles by microwave-assisted sand milling to obtain a slurry of sulfonated graphene-coated asphalt silicon particles; drying the slurry of sulfonated graphene-coated asphalt silicon particles and heat treating the slurry to obtain a graphene-coated silicon-carbon composite material.

[0025] The technical concept of the present invention is: the present application adds the triblock copolymer Pluronic F127 after the nano-silicon and asphalt are mixed and dispersed, and then the sulfonated graphene material is used for coating. In the subsequent calcination, Pluronic F127 will decompose to form porous carbon, H2O and CO2. During the process of these gases escaping from the inside, pores connecting the inside and outside of the material will be formed. These pores are conducive to the transmission of lithium ions to the inside of the material, and the formed porous carbon also provides a certain degree of slow release space for the volume expansion of nano-silicon during the charge and discharge process. The addition of zirconium oxide beads can promote the grinding and dispersion effect of materials such as nano-silicon and asphalt, and the agglomerated particles that may be formed are crushed through the sand milling process to avoid the formation of large particles. Sulfonated graphene is graphene modified by sulfonic acid groups, which is easier to disperse in hydrophilic solutions. It will form sulfur-doped graphene after sintering. The introduction of sulfur atoms can increase the carrier concentration in the electrochemical process, thereby improving the ion transmission effect. The use of sulfonated graphene for coating in silicon-carbon negative electrode can, firstly, improve the conductivity. Graphene itself has extremely high conductivity. As a derivative of graphene, sulfonated graphene can also provide good conductivity, which helps to reduce the internal resistance of the battery and improve the energy density and performance stability of the battery. Secondly, it can enhance the structural stability. Silicon will undergo severe volume expansion and contraction during the charging and discharging process, which may lead to material fracture and capacity loss. The sulfonated graphene coating can effectively resist this volume change and maintain the stability of the battery structure, thereby extending the service life and cycle number of the battery. Thirdly, it can improve the chemical stability. The sulfonated graphene coating can enhance the chemical stability of the silicon-carbon negative electrode material and avoid adverse reactions or oxidation with the electrolyte, which helps to reduce the battery energy loss and improve the safety of the battery. Fourthly, it can optimize the solid electrolyte interface (SEI) film. The sulfonated graphene coating can also help to form a stable SEI film, which can further protect the negative electrode material and improve the cycle stability and performance of the battery.

[0026] The present invention utilizes microwave-assisted sand milling technology to achieve uniform mixing and dispersion of asphalt silicon particles in a mixed solution of asphalt silicon particles and sulfonated graphene in a sulfonated graphene dispersion, thereby improving the uniformity and stability of the composite material; at the same time, by calcining the slurry of sulfonated graphene-coated asphalt silicon particles, the sulfonated graphene is reduced to sulfur-doped graphene, thereby effectively improving the electronic conductivity and cycle stability of the composite material. The coating of graphene prepared by the preparation method of the present application effectively buffers the volume effect generated by the silicon-based negative electrode material during the lithium insertion and extraction process, thereby extending the cycle life of the material. The method of the present invention is simple and easy to implement, has a high degree of practicality, and the prepared composite material has the advantages of good structural stability, large reversible capacity, and designable capacity.

[0027] Specifically, the preparation method of the graphene-coated silicon-carbon composite material comprises the following steps: 1) Add nano silicon powder to isopropanol of a certain mass ratio, mix and disperse them evenly by mechanical stirring, and obtain nano silicon dispersion; wherein the mass ratio of nano silicon powder to isopropanol is 1:(30-60); the speed of mechanical stirring is 600-900 rpm / min, and the time is 1-30h; 2) Add asphalt to isopropanol at a certain mass ratio, mix and disperse them evenly by mechanical stirring, and obtain an 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 1-30 hours; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), a certain mass of triblock copolymer Pluronic F127 and a certain mass of zirconia beads are sequentially added into a sand mill, and a mixed solution of asphalt silicon particles is obtained by microwave-assisted sand milling technology; wherein the mass ratio of nano-silicon in the nano-silicon dispersion to asphalt in the asphalt dispersion is 1:(5-10); the mass ratio of nano-silicon in the nano-silicon dispersion to triblock copolymer Pluronic F127 is 10:(1-3); the mass ratio of nano-silicon in the nano-silicon dispersion to zirconia beads is 1:(20-40), and the diameter of the zirconia beads is 5-20 mm; in the microwave-assisted sand milling, the microwave power is 500-2500 MHz, the sand milling speed is 800-2000 rpm / min, and the sand milling time is 6-24 h; 4) adding a certain amount of sulfonated graphene dispersion to the mixed solution of step 3) so that the asphalt silicon particles are dispersed in the sulfonated graphene dispersion, further grinding and dispersing by microwave-assisted sand milling technology so that the asphalt silicon particles are uniformly coated with sulfonated graphene to obtain a slurry of sulfonated graphene-coated asphalt silicon particles; wherein the mass ratio of nano-silicon in the mixed solution of asphalt silicon particles to the mass ratio of sulfonated graphene in the sulfonated graphene dispersion is 1:(0.02-0.05), and the mass concentration range of the sulfonated graphene dispersion is 1-5 mg / mL; in the microwave-assisted sand milling, the microwave power is 500-2500 MHz, the sand milling speed is 800-2000 rpm / min, and the sand milling time is 1-4 h; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged and dried, and then sintered in a high-temperature tubular furnace, using nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material; wherein the calcination temperature is 600-1000 °C, and the time is 60-300 min.

[0028] The implementation process of the present invention is described in detail below in conjunction with specific embodiments. However, it will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail with reference to the embodiments below. It should be noted that the endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0029] In the following examples, the raw material used, triblock copolymer Pluronic F127, has a molecular weight of 12600 and a CAS number of 9003-11-6. The remaining raw materials used are all commercially available products that can be purchased directly or can be prepared according to conventional techniques in the art.

[0030] 1. Specific embodiments of the method for preparing the graphene-coated silicon-carbon composite material of the present invention Example 1 The method for preparing the graphene-coated silicon-carbon composite material provided in this embodiment comprises the following steps: 1) Add 1 g of nano-silicon powder to 30 g of isopropanol and mix and disperse them evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein the speed of the mechanical stirring is 600 rpm / min and the time is 1 h; 2) Add 5 g of asphalt into 50 g of isopropanol and mix and disperse them evenly by mechanical stirring to obtain an asphalt dispersion; wherein the speed of the mechanical stirring is 600 rpm / min and the time is 1 hour; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), 0.1 g of Pluronic F127 and 20 g of zirconia beads with a diameter of 5 mm are sequentially added into a sand milling jar, and a mixed solution of asphalt silicon particles is obtained by microwave-assisted sand milling technology; wherein 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 6 hours; 4) adding 10 mL of 5 mg / mL sulfonated graphene dispersion to the mixed solution of step 3) to disperse the asphalt silicon particles in the sulfonated graphene dispersion, further grinding and dispersing the asphalt silicon particles by microwave-assisted sand milling technology to uniformly coat the asphalt silicon particles with the sulfonated graphene, and obtaining a slurry of sulfonated graphene-coated asphalt silicon particles; wherein 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; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged to remove isopropanol, and then placed in a 60°C oven for 24 hours; then sintered at 600°C for 300 minutes in a high-temperature tubular furnace with nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material.

[0031] Example 2 The method for preparing the graphene-coated silicon-carbon composite material provided in this embodiment comprises the following steps: 1) Add 1 g of nano-silicon powder to 50 g of isopropanol and mix and disperse them evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein the speed of the mechanical stirring is 800 rpm / min and the time is 20 h; 2) Add 6 g of asphalt into 90 g of isopropanol and mix and disperse them evenly by mechanical stirring to obtain an asphalt dispersion; wherein the speed of the mechanical stirring is 800 rpm / min and the time is 24 hours; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), 0.2 g of Pluronic F127 and 30 g of zirconia beads with a diameter of 10 mm are sequentially added into a sand milling jar, and a mixed solution of asphalt silicon particles is obtained by microwave-assisted sand milling technology; wherein 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 12 h; 4) adding 10 mL of 4 mg / mL sulfonated graphene dispersion to the mixed solution of step 3) to disperse the asphalt silicon particles in the sulfonated graphene dispersion, further grinding and dispersing the asphalt silicon particles by microwave-assisted sand milling technology to uniformly coat the asphalt silicon particles with the sulfonated graphene, and obtaining a slurry of sulfonated graphene-coated asphalt silicon particles; wherein 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 3 h; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged to remove isopropanol, and then placed in a 60°C oven for drying for 36 hours; then sintered at 900°C for 60 minutes in a high-temperature tubular furnace with nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material.

[0032] Example 3 The method for preparing the graphene-coated silicon-carbon composite material provided in this embodiment comprises the following steps: 1) Add 1g of nano-silicon powder to 60g of isopropanol, and mix and disperse them evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein the speed of the mechanical stirring is 900 rpm / min, and the time is 30h; 2) 10 g of asphalt was added to 200 g of isopropanol, and the mixture was uniformly dispersed by mechanical stirring to obtain an asphalt dispersion; the speed of the mechanical stirring was 900 rpm / min, and the stirring time was 30 h; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), 0.3 g of Pluronic F127 and 40 g of zirconia beads with a diameter of 20 mm are sequentially added into a sand milling jar, and a mixed solution of asphalt silicon particles is obtained by microwave-assisted sand milling technology; wherein 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 24 h; 4) adding 20 mL of 1 mg / mL sulfonated graphene dispersion to the mixed solution of step 3) to disperse the asphalt silicon particles in the sulfonated graphene dispersion, further grinding and dispersing the asphalt silicon particles by microwave-assisted sand milling technology to uniformly coat the asphalt silicon particles with the sulfonated graphene, and obtaining a slurry of sulfonated graphene-coated asphalt silicon particles; wherein 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 hour; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged to remove isopropanol, and then placed in a 70°C oven for drying for 24 hours; then sintered at 1000°C for 180 minutes in a high-temperature tubular furnace with nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material.

[0033] Example 4 The method for preparing the graphene-coated silicon-carbon composite material provided in this embodiment comprises the following steps: 1) Add 1g of nano-silicon powder to 40g of isopropanol, and mix and disperse them evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein the speed of the mechanical stirring is 750 rpm / min, and the time is 10h; 2) 8 g of asphalt was added to 120 g of isopropanol, and the mixture was uniformly dispersed by mechanical stirring to obtain an asphalt dispersion; wherein the speed of the mechanical stirring was 750 rpm / min, and the stirring time was 10 h; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), 0.15 g of Pluronic F127 and 30 g of zirconia beads with a diameter of 15 mm were sequentially added into a sand milling jar, and a mixed solution of asphalt silicon particles was obtained by microwave-assisted sand milling technology; wherein the microwave power in the microwave-assisted sand milling was 1500 MHz, the sand milling speed was 2000 rpm / min, and the sand milling time was 8 hours; 4) adding 10 mL of 3 mg / mL sulfonated graphene dispersion to the mixed solution of step 3) to disperse the asphalt silicon particles in the sulfonated graphene dispersion, further grinding and dispersing the asphalt silicon particles by microwave-assisted sand milling technology to uniformly coat the asphalt silicon particles with the sulfonated graphene, and obtaining a slurry of sulfonated graphene-coated asphalt silicon particles; wherein 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 2 h; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged to remove isopropanol, and then placed in a 60°C oven for drying for 24 hours; then sintered at 1000°C for 60 minutes in a high-temperature tubular furnace with nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material.

[0034] Example 5 The method for preparing the graphene-coated silicon-carbon composite material provided in this embodiment comprises the following steps: 1) Add 1g of nano-silicon powder to 60g of isopropanol, and mix and disperse them evenly by mechanical stirring to obtain a uniform nano-silicon dispersion; wherein the speed of the mechanical stirring is 800 rpm / min, and the time is 20h; 2) 6 g of asphalt was added to 120 g of isopropanol and mixed and dispersed uniformly by mechanical stirring to obtain an asphalt dispersion; wherein the speed of the mechanical stirring was 800 rpm / min and the stirring time was 20 h; 3) The nano-silicon dispersion in step 1), the asphalt dispersion in step 2), 0.2 g of Pluronic F127 and 40 g of zirconia beads with a diameter of 5 mm are sequentially added into a sand milling jar, and a mixed solution of asphalt silicon particles is obtained by microwave-assisted sand milling technology; wherein 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 12 h; 4) adding 15 mL of 3 mg / mL sulfonated graphene dispersion to the mixed solution of step 3) to disperse the asphalt silicon particles in the sulfonated graphene dispersion, further grinding and dispersing the asphalt silicon particles by microwave-assisted sand milling technology to uniformly coat the asphalt silicon particles with the sulfonated graphene, and obtaining a slurry of sulfonated graphene-coated asphalt silicon particles; wherein 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 hours; 5) The slurry of sulfonated graphene-coated asphalt silicon particles obtained in step 4) is centrifuged to remove isopropanol, and then placed in a 60°C oven for drying for 24 hours; then sintered at 900°C for 180 minutes in a high-temperature tubular furnace with nitrogen as a protective gas, and the black solid obtained by calcination is crushed and sieved to obtain a graphene-coated silicon-carbon composite material.

[0035] 2. Experimental Examples Experimental Example 1 XRD Characterization The graphene-coated silicon-carbon composite material prepared in Example 5 was characterized by XRD. Specifically, the graphene-coated silicon-carbon composite material prepared was detected by using a BrukeD8 Advance XRD. The results are as follows: Figure 1 It can be seen that 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 is successfully prepared.

[0036] Experimental Example 2 SEM Characterization The graphene-coated silicon-carbon composite material prepared in Example 5 was subjected to SEM characterization. Specifically, the morphology of the graphene-coated silicon-carbon composite material was characterized using a ZeissSigma 300 SEM. The results are as follows: Figure 2 It can be seen that the graphene-coated silicon-carbon composite material prepared in Example 5 is uniformly coated particles.

[0037] Experimental Example 3 Electrochemical Performance The graphene-coated silicon-carbon composite materials prepared in the above-mentioned embodiments 1-5 were subjected to electrochemical performance testing. Specifically, the preparation method of the button cell used for testing the electrochemical performance is as follows: the graphene-coated silicon-carbon composite materials prepared in embodiments 1-5 were respectively used as the battery negative electrode material and mixed with CMC, SBR and conductive agent (super P) in a ratio of 70:4:6:20 and evenly coated on copper foil, and vacuum dried as the negative electrode, with lithium metal as the counter electrode, the electrolyte used was a mixture of 1M LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) in a mass ratio of 1:1, and the separator was a PE / PP / PE composite film, assembled into a CR2032 button cell. The test conditions are: the rate charge and discharge is carried out at a current density of 0.1~1 A / g, the charging voltage is limited to 0.01~3 V, and the charge and discharge test is carried out at different current densities. The results are shown in Table 1.

[0038] Table 1 Discharge specific capacity of Examples 1-5 at different current densities

[0039] It can be seen from Table 1 that at a current density of 100 mA / g, the discharge specific capacity of the graphene-coated silicon-carbon composite material prepared in Examples 1-5 is the largest, which is above 663.2 mAh / g and can reach up to 1194.7 mAh / g. It can also be shown that the graphene-coated silicon-carbon composite material prepared in Examples 1-5 has good electrochemical performance.

[0040] At the same time, the graphene-coated silicon-carbon composite material prepared in Example 5 was tested for rate performance at different current densities. The results are as follows: Figure 3 As shown. It can be seen that the charge and discharge cycle of the graphene-coated silicon-carbon composite material prepared in Example 5 is basically stable at different current densities, indicating that the material synthesized in the present invention has good rate performance. The AC impedance test in the frequency range of 0.01Hz~100KHz, the results are as follows Figure 4 It can be seen that the radius of the small semicircle of the test curve in the high-frequency region is small, indicating that the electrochemical impedance of the graphene-coated silicon-carbon composite material prepared in Example 5 is small, and 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, has good electrochemical performance.

[0041] This shows that the graphene-coated silicon-carbon composite material prepared by the preparation method of the graphene-coated silicon-carbon composite material provided in the present 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.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a graphene-coated silicon-carbon composite material, characterized in that: The following steps are involved: The nano-silicon dispersion, the asphalt dispersion, the triblock copolymer Pluronic F127 and the zirconium oxide beads are mixed by microwave-assisted sand milling to obtain a mixed solution of asphalt silicon particles; The sulfonated graphene dispersion is added to the mixed solution of asphalt silicon particles for microwave-assisted sand milling dispersion to obtain a slurry of sulfonated graphene-coated asphalt silicon particles; The slurry of sulfonated graphene-coated asphalt silicon particles is dried and then calcined to obtain a graphene-coated silicon-carbon composite material.

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

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

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

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

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

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

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

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

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

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