Graphene-like carbon-coated silicon / carbon / graphene composite material, preparation method thereof and anode material

Abstract

The present invention provides a graphene-like carbon-coated silicon / carbon / graphene composite material, a preparation method thereof, and a negative electrode material. Calculated by mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material comprises: 1-10% of a graphene-like carbon coating layer, 1-15% of silicon, 80-95% of carbon, and 0.1-5% of graphene. Using the graphene-like carbon-coated silicon / carbon / graphene composite material as an electrode of a battery can greatly reduce the cost and achieve large-scale production. In the graphene-like carbon-coated silicon / carbon / graphene composite material of the present application, the nano-silicon is wrapped by a double carbon layer of graphene and graphene-like carbon, which can effectively alleviate the volume effect of the nano-silicon, thereby avoiding direct contact between the nano-silicon and the electrolyte, and further improving the cycle stability of the Si / C composite material. Moreover, the graphene-like carbon-coated silicon / carbon / graphene composite material has good electrical conductivity, high specific capacity, wide raw material sources, and is economical and environmentally friendly.

Description

Technical Field

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

[0002] With the rapid development of portable electronic devices and electric vehicles, and the increasing demand for high-energy electronic devices, it is urgent to develop high-energy density batteries. However, the theoretical capacity of commercial graphite negative electrodes is relatively low (372 mAh / g), which cannot meet the increasing demand for high-energy electronic devices. Silicon negative electrode materials have attracted great attention due to their highest theoretical specific capacity (about 4200 mAh / g) and relatively low (compared with Li / Li + discharge potential (<0.5 V). However, silicon has low electrical conductivity, and silicon will produce a huge volume expansion effect during the process of lithium ion insertion / extraction, which will cause pulverization of the electrode material and separation of the active material, and then lead to poor cycling performance. At the same time, the volume expansion is easy to cause the rupture of the solid electrolyte interface (SEI) film. Many researchers have tried to construct various Si / C composite materials, including graphite or graphitized carbon, amorphous carbon, graphene or N-doped graphene, carbon nanotubes, carbon fibers, and porous carbon. The C in the Si / C composite can not only relieve the volume effect, but also improve the electronic conductivity of the Si / C composite material, and can form a stable solid electrolyte interface (SEI) on the electrode surface. However, the cycling stability of the Si / C composite materials in the prior art is still poor. Summary of the Invention

[0003] The main object of the present invention is to provide a graphene-like carbon-coated silicon / carbon / graphene composite material, a preparation method thereof, and a negative electrode material, so as to solve the problem of poor cycling stability of the Si / C composite materials in the prior art.

[0004] To achieve the above object, according to one aspect of the present invention, there is provided a graphene-like carbon-coated silicon / carbon / graphene composite material. In terms of mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material includes: 1-10% of a graphene-like carbon coating layer, 1-15% of silicon, 80-95% of carbon, and 0.1-5% of graphene.

[0005] Further, the thickness of the graphene-like carbon coating layer of the above graphene-like carbon-coated silicon / carbon / graphene composite material is 5 nm. Preferably, the particle size of the graphene-like carbon-coated silicon / carbon / graphene composite material is 23-30 μm. Preferably, in terms of mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material includes: 1-7% of a graphene-like carbon coating layer, 5-15% of silicon, 83-90% of carbon, and 0.1-3% of graphene.

[0006] To achieve the above object, according to another aspect of the present invention, there is provided a method for preparing the above-mentioned graphene-like carbon-coated silicon / carbon / graphene composite material, and the preparation method includes: Step S1, mixing a nano-silicon solution, a phenolic resin solution, a graphene slurry and graphite to obtain a mixture; Step S2, drying the mixture to obtain a dried composite material powder; Step S3, in an inert atmosphere, mixing the dried composite material powder, a carbon source and a foaming agent and then performing a heat treatment to obtain a carbon-coated composite material; and Step S4, calcining the carbon-coated composite material to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material.

[0007] Further, in the above-mentioned Step S3, the mass ratio of the dried composite material powder, the carbon source and the foaming agent is 90-95:5-10:5-10. Preferably, the carbon source is selected from any one or more of glucose, sucrose, and maltose. Preferably, the foaming agent is selected from any one or more of ammonium chloride, ammonium sulfate, and ammonium carbonate.

[0008] Further, in the above-mentioned Step S3, the temperature of the heat treatment is 200-400°C, preferably 250-400°C, and the time of the heat treatment is 1-5 h, preferably 1-3 h.

[0009] Further, in the above-mentioned Step S4, the temperature of the calcination is 500-1500°C, preferably 1200-1500°C, and the time of the calcination is 1-10 h, preferably 5-10 h.

[0010] Further, in the above-mentioned Step S1, by mass percentage, the dried composite material powder includes 5-15% of nano-silicon, 1-4% of phenolic resin, 0.1-2% of graphene and 80-90% of graphite. Preferably, the dried composite material powder includes 8-12% of nano-silicon, 2-3% of phenolic resin, 0.2-1% of graphene and 84-89% of graphite.

[0011] Further, in the above-mentioned Step S2, the drying is spray drying. Preferably, the temperature of the spray drying is 100-200°C.

[0012] Further, before the above-mentioned Step S1, the preparation method further includes: ball-milling a silicon source with a particle size of 100-200 μm in an organic solvent to obtain a nano-silicon solution; preferably, the silicon source is silicon powder, preferably, the organic solvent is selected from any one or more of ethanol, ethylene glycol, and isopropanol. Preferably, the mass ratio of the grinding balls to the silicon source is 1.4-2.2:1, further optimized to 1.6-2.2:1. Preferably, the grinding balls are zirconia grinding balls. Preferably, the particle size of the zirconia grinding balls is 0.1-1 mm. Preferably, the speed of the ball-milling is 2000 rpm / min, and the time of the ball-milling is 1-6 h.

[0013] According to another aspect of the present invention, a negative electrode material is provided, which includes the aforementioned graphene-like carbon-coated silicon / carbon / graphene composite material.

[0014] Applying the technical solution of the present invention, graphene is considered an ideal composite matrix for the negative electrode material of lithium-ion batteries due to its excellent properties: its large surface area can increase the storage density of lithium ions, good mechanical flexibility can effectively alleviate the structural changes during the electrochemical reaction process, and excellent electrical conductivity can ensure the minimum ohmic loss during the discharge and charge reactions of the negative electrode. However, graphene is expensive. Therefore, in this application, a composite material is formed by coating silicon / carbon / graphene with graphene-like carbon. The cost of graphene-like carbon is much lower than that of graphene. Therefore, using graphene-like carbon to replace part of graphene as the coating material can reduce the cost of the composite material. When this composite material is used as the electrode of the battery, the cost can be greatly reduced, and large-scale mass production can be achieved. The nanosilicon in the graphene-like carbon-coated silicon / carbon / graphene composite material of this application is wrapped by a double carbon layer of graphene and graphene-like carbon, which can effectively alleviate the volume effect of nanosilicon, thus avoiding the direct contact between nanosilicon and the electrolyte, and further improving the cycle stability of the Si / C composite material. Moreover, the graphene-like carbon-coated silicon / carbon / graphene composite material has good electrical conductivity, high specific capacity, wide raw material sources, and is economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0016] Figure 1 shows a scanning electron microscope image of a graphene-like carbon-coated silicon / carbon / graphene composite material provided in Example 1 according to the present invention; and

[0017] Figure 2 shows a cycle performance graph of a graphene-like carbon-coated silicon / carbon / graphene composite material provided in Example 1 according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0019] As analyzed in the background art, there is a problem of poor cycle stability of the Si / C composite material in the prior art. To solve this problem, the present invention provides a graphene-like carbon-coated silicon / carbon / graphene composite material, its preparation method, and a negative electrode material.

[0020] In a typical embodiment of the present application, a graphene-like carbon-coated silicon / carbon / graphene composite material is provided. By mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material comprises: 1-10% of a graphene-like carbon coating layer, 1-15% of silicon, 80-95% of carbon, and 0.1-5% of graphene.

[0021] Graphene is considered an ideal composite matrix for the anode material of lithium-ion batteries due to its excellent properties: its large surface area can increase the storage density of lithium ions, good mechanical flexibility can effectively alleviate the structural changes during the electrochemical reaction process, and excellent electrical conductivity can ensure minimal ohmic loss during the discharge and charge reactions of the anode. However, graphene is expensive. Therefore, in the present application, a composite material is formed by coating silicon / carbon / graphene with graphene-like carbon. The cost of graphene-like carbon is much lower than that of graphene. Therefore, using graphene-like carbon to replace part of the graphene as the coating material can reduce the cost of the composite material. When this composite material is used as the electrode of the battery, the cost can be greatly reduced, and large-scale production can be achieved. The nanosilicon in the graphene-like carbon-coated silicon / carbon / graphene composite material of the present application is wrapped by a double carbon layer of graphene and graphene-like carbon, which can effectively alleviate the volume effect of nanosilicon, thus avoiding the direct contact between nanosilicon and the electrolyte, and further improving the cycle stability of the Si / C composite material. Moreover, the graphene-like carbon-coated silicon / carbon / graphene composite material has good electrical conductivity, high specific capacity, wide raw material sources, and is economical and environmentally friendly.

[0022] In an embodiment of the present application, the thickness of the graphene-like carbon coating layer of the above-mentioned graphene-like carbon-coated silicon / carbon / graphene composite material is 5 nm. Preferably, the particle size of the graphene-like carbon-coated silicon / carbon / graphene composite material is 23-30 μm. Preferably, by mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material comprises: 1-7% of a graphene-like carbon coating layer, 5-15% of silicon, 83-90% of carbon, and 0.1-3% of graphene.

[0023] The graphene-like carbon-coated silicon / carbon / graphene composite material with a thickness, particle size, and each component content within the above ranges has better cycle stability and electrical conductivity.

[0024] In another typical embodiment of the present application, a preparation method of the aforementioned graphene-like carbon-coated silicon / carbon / graphene composite material is provided. The preparation method includes: Step S1, mixing a nano-silicon solution, a phenolic resin solution, a graphene slurry, and graphite to obtain a mixture; Step S2, drying the mixture to obtain a dried composite material powder; Step S3, in an inert atmosphere, mixing the dried composite material powder, a carbon source, and a foaming agent, and then performing a heat treatment to obtain a carbon-coated composite material; and Step S4, calcining the carbon-coated composite material to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material.

[0025] During the heating process of the carbon source, it first melts into a liquid slurry. The liquid slurry will gradually polymerize to obtain a macromolecular polymer and wrap on the surface of the composite material powder. The chemical gas released by the foaming agent will blow out the macromolecular polymer. Continuing to heat, as the gas is released, the surface tension of the polymer liquid is released and gradually becomes thinner, obtaining a polymer thin layer closely adhering to the surface of the composite material powder. This polymer thin layer is then transformed into a graphene-like carbon coating layer through high-temperature calcination and coated on the surface of silicon / carbon / graphene. And because it acts on the surface of silicon / carbon / graphene during the formation process of the above-mentioned graphene-like, therefore, the formed graphene-like carbon coating layer is more tightly combined with silicon / carbon / graphene, thereby further avoiding the direct contact between nano-silicon and the electrolyte, and then improving the cycle stability of the Si / C composite material. And the above preparation method is simple, the raw material sources are wide, and it is economical and environmentally friendly.

[0026] In order to make the carbon source and the foaming agent act more fully to form a graphene-like coating layer and cover the silicon material as much as possible, thereby effectively alleviating the volume effect of nano-silicon, preferably in the above Step S3, the mass ratio of the dried composite material powder, the carbon source, and the foaming agent is 90-95:5-10:5-10. Preferably, the carbon source is selected from any one or more of glucose, sucrose, and maltose. Preferably, the foaming agent is selected from any one or more of ammonium chloride, ammonium sulfate, and ammonium carbonate.

[0027] The above carbon source has wide sources, is clean and environmentally friendly, and can avoid the generation of harmful gases by the coating of asphalt-like carbon sources and pollute the environment.

[0028] In an embodiment of the present application, in the above Step S3, the temperature of the heat treatment is 200-400 °C, preferably 250-400 °C, and the time of the heat treatment is 1-5 h, preferably 1-3 h.

[0029] Controlling the temperature and time of the heat treatment within the above ranges helps the carbon source and the foaming agent to act better, thereby helping to form the carbon coating layer of the carbon-coated composite material.

[0030] In order to promote the conversion of the carbon coating layer of the carbon-coated composite material into a graphene-like coating layer, preferably in the above step S4, the calcination temperature is 500-1500° C., preferably 1200-1500° C., and the calcination time is 1-10 h, preferably 5-10 h.

[0031] In one embodiment of the present application, in the above step S1, the composite material powder after drying includes 5-15% nano-silicon, 1-4% phenolic resin, 0.1-2% graphene and 80-90% graphite, by mass percentage. Preferably, the composite material powder after drying includes 8-12% nano-silicon, 2-3% phenolic resin, 0.2-1% graphene and 84-89% graphite.

[0032] The present application combines the characteristics of graphene and graphite with the advantages and disadvantages of nano-silicon, and controls the usage of the three within the above range, which helps to improve the conductivity and specific capacity of the resulting graphene-like carbon-coated silicon / carbon / graphene composite material. Phenolic resin is used as a binder to help bond the above conductive materials into shape.

[0033] In one embodiment of the present application, in the above step S2, the drying is spray drying, and the spray drying temperature is preferably 100-200°C.

[0034] The spray granulation technology is used to make the synthesized dried composite material powder have a good spherical morphology, good overall consistency and high drying efficiency, which helps to improve the stability of the final graphene-like carbon-coated silicon / carbon / graphene composite material. The above-mentioned spray drying conditions are conducive to further improving the drying effect.

[0035] In order to obtain nano-silicon with a particle size that is more in line with the requirements for preparing graphene-like carbon-coated silicon / carbon / graphene composite materials in the present application, it is preferred that before the above-mentioned step S1, the preparation method further includes: ball milling a silicon source with a particle size of 100 to 200 μm in an organic solvent to obtain a nano-silicon solution; preferably, the silicon source is silicon powder, and the organic solvent is preferably selected from any one or more of ethanol, ethylene glycol, and isopropanol. Preferably, the mass ratio of the grinding balls to the silicon source is 1.4 to 2.2:1, further optimized to 1.6 to 2.2:1, preferably, the grinding balls are zirconia grinding balls, and preferably the particle size of the zirconia grinding balls is 0.1 to 1 mm, preferably, the ball milling speed is 2000 rpm / min, and the ball milling time is 1 to 6 h.

[0036] In another typical embodiment of the present application, a negative electrode material is provided, wherein the negative electrode material comprises any one of the aforementioned graphene-like carbon-coated silicon / carbon / graphene composite materials.

[0037] Although graphene is considered an ideal composite matrix for the negative electrode material of lithium-ion batteries due to its excellent properties: its large surface area can increase the storage density of lithium ions, good mechanical flexibility can effectively alleviate the structural changes during the electrochemical reaction process, and excellent electrical conductivity can ensure minimal ohmic loss during the discharge and charge reactions of the negative electrode. However, graphene is expensive. Therefore, in this application, graphene-like carbon-coated silicon / carbon / graphene is used to form a composite material. The cost of graphene-like is much lower than that of graphene. Therefore, using graphene-like to replace part of graphene as the coating material can reduce the cost of the composite material. When this composite material is used as the electrode of the battery, the cost can be greatly reduced, and large-scale production can be achieved. The nano-silicon in the graphene-like carbon-coated silicon / carbon / graphene composite material of this application is wrapped by a double carbon layer of graphene and graphene-like, which can effectively alleviate the volume effect of nano-silicon, thus avoiding the direct contact between nano-silicon and the electrolyte, and further improving the cycle stability of the Si / C composite material. Moreover, this graphene-like carbon-coated silicon / carbon / graphene composite material has good electrical conductivity, high specific capacity, wide raw material sources, and is economical and environmentally friendly.

[0038] The beneficial effects of this application will be described below in conjunction with specific examples and comparative examples.

[0039] Example 1

[0040] Weigh 400 g of silicon powder with a particle size of 100 μm, and use zirconia grinding balls with a particle size of 0.1 mm to ball-mill it. The mass ratio of the balls to the material is 1.6:1, and the solvent is ethanol. After mixing evenly, add the mixed solution into a nano sand mill and ball-mill it at a ball-milling speed of 2000 rpm / min for 5 h to obtain a nano-silicon solution with a mass concentration of 0.13 g / mL.

[0041] Mix 3000 mL of the nano-silicon solution with 500 mL of a phenolic resin ethanol solution with a mass concentration of 0.2 g / mL, 500 mL of a graphene slurry with a mass concentration of 0.03 g / mL, and 4485 g of graphite, stir until uniform, and then use a high-speed grinding and dispersing machine to grind and disperse the mixture at a speed of 2000 rpm for 2 hours to obtain a mixture. Spray-dry the mixture at 160 °C for 0.5 h to obtain the dried composite material powder. The dried composite material powder includes 8% nano-silicon, 2% phenolic resin, 0.1% graphene, and 89.9% graphite.

[0042] Add 4000 g of the dried composite material powder into a high-temperature coating furnace, and then weigh glucose and ammonium chloride. The mass ratio of the dried composite material powder, glucose, and ammonium chloride is 93:7:7. Heat it to 400 °C under an argon atmosphere condition at a heating rate of 5 °C / min and keep it warm for 3 hours to obtain a carbon-coated composite material.

[0043] Transfer the carbon-coated composite material to a rotary kiln furnace. Under argon protection, heat it to 1200 °C at a heating rate of 5 °C / min and carbonize for 5 h, then naturally cool it to room temperature in argon to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating layer, 8% silicon, 88.7% carbon, and 0.3% graphene, where the thickness of the graphene-like carbon coating layer is 5 nm. The scanning electron microscope image of this graphene-like carbon-coated silicon / carbon / graphene composite material is as shown in Figure 1 shown, and the cycling performance graph of this graphene-like carbon-coated silicon / carbon / graphene composite material is as shown in Figure 2 shown.

[0044] Example 2

[0045] The difference between Example 2 and Example 1 is that the mass ratio of the dried composite material powder, glucose, and ammonium chloride is 95:5:5, obtaining a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 23 μm, containing 1% graphene-like carbon coating layer, 10% silicon, 88.7% carbon, and 0.3% graphene.

[0046] Example 3

[0047] The difference between Example 3 and Example 1 is that the mass ratio of the dried composite material powder, glucose, and ammonium chloride is 90:10:10, obtaining a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 28 μm, containing 7% graphene-like carbon coating layer, 5% silicon, 87.9% carbon, and 0.1% graphene.

[0048] Example 4

[0049] The difference between Example 4 and Example 1 is that the mass ratio of the dried composite material powder, glucose, and ammonium chloride is 80:20:20, obtaining a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 30 μm, containing 8% graphene-like carbon coating layer, 3% silicon, 88.9% carbon, and 0.1% graphene.

[0050] Example 5

[0051] The difference between Example 5 and Example 1 is that it is heated to 250 °C under an argon atmosphere condition to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating layer, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0052] Example 6

[0053] Example 6 is different from Example 1 in that it is heated to 200 °C for 1 h under an argon atmosphere to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0054] Example 7

[0055] Example 7 is different from Example 1 in that it is heated to 150 °C under an argon atmosphere to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0056] Example 8

[0057] Example 8 is different from Example 1 in that the carbon-coated composite material is transferred to a rotary kiln furnace and heated to 1500 °C under argon gas protection for carbonization for 8 h to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0058] Example 9

[0059] Example 9 is different from Example 1 in that the carbon-coated composite material is transferred to a rotary kiln furnace and heated to 1300 °C under argon gas protection for carbonization for 10 h to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0060] Example 10

[0061] Example 10 is different from Example 1 in that the carbon-coated composite material is transferred to a rotary kiln furnace and heated to 500 °C under argon gas protection for carbonization for 1 h to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0062] Example 11

[0063] Example 11 is different from Example 1 in that the carbon-coated composite material is transferred to a rotary kiln furnace and heated to 400 °C under argon gas protection for carbonization for 1 h to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 25 μm, containing 3% graphene-like carbon coating, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0064] Example 12

[0065] The difference between Example 12 and Example 1 is that 400 g of silicon powder with a particle size of 150 μm was weighed, and zirconia grinding balls with a particle size of 0.6 mm were used to ball-mill it. The mass ratio of balls to materials was 1.4:1, and the solvent was ethanol. After mixing evenly, the mixed solution was added to a nano sand mill and ball-milled at a ball-milling speed of 1500 rpm / min for 10 h to obtain a nano-silicon solution with a mass concentration of 0.13 g / mL.

[0066] 3000 mL of the nano-silicon solution was mixed with 500 mL of a phenolic resin ethanol solution with a mass concentration of 0.2 g / mL, 500 mL of a graphene slurry with a mass concentration of 0.03 g / mL, and 4485 g of graphite, and stirred until homogeneous. Then, the mixture was ground and dispersed with a high-speed grinding and dispersing machine for 2 h to obtain a mixture. The mixture was spray-dried at 180 °C for 0.2 h to obtain a dried composite material powder, which included 8% nano-silicon, 2% phenolic resin, 0.1% graphene, and 89.9% graphite.

[0067] A graphene-like carbon-coated silicon / carbon / graphene composite material with a particle size (D50) of 32 μm was obtained, which included 3% graphene-like carbon coating layer, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0068] Example 13

[0069] The difference between Example 13 and Example 1 is that 400 g of silicon powder with a particle size of 200 μm was weighed, and zirconia grinding balls with a particle size of 1 mm were used to ball-mill it. The mass ratio of balls to materials was 2.2:1, and the solvent was ethylene glycol. After mixing evenly, the mixed solution was added to a nano sand mill and ball-milled at a ball-milling speed of 2500 rpm / min for 2 h to obtain a nano-silicon solution with a mass concentration of 0.13 g / mL.

[0070] 3000 mL of the nano-silicon solution was mixed with 500 mL of a phenolic resin ethanol solution with a mass concentration of 0.2 g / mL, 500 mL of a graphene slurry with a mass concentration of 0.03 g / mL, and 4485 g of graphite, and stirred until homogeneous. Then, the mixture was ground and dispersed with a high-speed grinding and dispersing machine for 2 h to obtain a mixture. The mixture was spray-dried at 150 °C for 1 h to obtain a dried composite material powder, which included 8% nano-silicon, 2% phenolic resin, 0.1% graphene, and 89.9% graphite.

[0071] A graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, with a particle size (D50) of 22 μm, containing 3% graphene-like carbon coating layer, 8% silicon, 88.7% carbon, and 0.3% graphene.

[0072] Example 14

[0073] The difference between Example 14 and Example 1 is that 3000 mL of nano-silicon solution is mixed with 1000 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 1111 mL of graphene slurry with a mass concentration of 0.03, and 2800 g of graphite, stirred until homogeneous, and then the mixture is ground and dispersed for 2 hours using a high-speed grinding and dispersing machine to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder, which includes 12% nano-silicon, 4% phenolic resin, 0.2% graphene, and 83.8% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, containing 10% graphene-like carbon coating layer, 9.8% silicon, 80% carbon, and 0.2% graphene.

[0074] Example 15

[0075] The difference between Example 15 and Example 1 is that 3000 mL of nano-silicon solution is mixed with 1000 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 667 mL of graphene slurry with a mass concentration of 0.03, and 3480 g of graphite, stirred until homogeneous, and then the mixture is ground and dispersed for 2 hours using a high-speed grinding and dispersing machine to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder, which includes 9% nano-silicon, 1% phenolic resin, 1% graphene, and 89% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, containing 3% graphene-like carbon coating layer, 9% silicon, 83% carbon, and 5% graphene.

[0076] Example 16

[0077] Example 16 is different from Example 1 in that 1500 mL of nano-silicon solution is mixed with 600 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 1333 mL of graphene slurry with a mass concentration of 0.03, and 3460 g of graphite, stirred until homogeneous, and then the mixture is ground and dispersed for 2 hours by a high-speed grinding and dispersing machine to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder. The dried composite material powder includes 5% nano-silicon, 4% phenolic resin, 1% graphene, and 90% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, which contains 3% graphene-like carbon coating layer, 5% silicon, 90% carbon, and 2% graphene.

[0078] Example 17

[0079] Example 17 is different from Example 1 in that 3500 mL of nano-silicon solution is mixed with 175 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 583 mL of graphene slurry with a mass concentration of 0.03, and 2993 g of graphite, stirred until homogeneous, and then the mixture is ground and dispersed for 2 hours by a high-speed grinding and dispersing machine to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder. The dried composite material powder includes 13% nano-silicon, 1% phenolic resin, 0.5% graphene, and 85.5% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, which contains 3% graphene-like carbon coating layer, 10% silicon, 83% carbon, and 4% graphene.

[0080] Example 18

[0081] Example 18 is different from Example 1 in that 4000 mL of nano-silicon solution is mixed with 693 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 1155 mL of graphene slurry with a mass concentration of 0.03, and 2773 g of graphite, stirred until homogeneous, and then the mixture is ground and dispersed for 2 hours by a high-speed grinding and dispersing machine to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder. The dried composite material powder includes 15% nano-silicon, 3% phenolic resin, 2% graphene, and 80% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, which contains 2% graphene-like carbon coating layer, 15% silicon, 80% carbon, and 3% graphene.

[0082] Example 19

[0083] Example 19 is different from Example 1 in that 1500 mL of nano-silicon solution is mixed with 420 mL of phenolic resin ethanol solution with a mass concentration of 0.2, 1655 mL of graphene slurry with a mass concentration of 0.03, and 3120 g of graphite, and stirred until homogeneous. Then, the mixture is ground and dispersed by a high-speed grinding disperser for 2 hours to obtain a mixture. The mixture is spray-dried at 160 °C for 0.5 h to obtain a dried composite material powder. The dried composite material powder contains 5% nano-silicon, 2% phenolic resin, 3% graphene, and 90% graphite. Finally, a graphene-like carbon-coated silicon / carbon / graphene composite material is obtained, which contains 1% graphene-like carbon coating layer, 3% silicon, 95% carbon, and 1% graphene.

[0084] Comparative Example 1

[0085] Comparative Example 1 is different from Example 1 in that

[0086] the dried composite material powder is not carbon-coated, and the remaining operations are the same as those in Example 1 to obtain a silicon / carbon / graphene composite material.

[0087] Comparative Example 2

[0088] Comparative Example 2 is different from Example 1 in that

[0089] a graphene-like material is prepared first, and then the silicon / carbon / graphene material is coated. The remaining operations are the same as those in Example 1, specifically as follows:

[0090] Glucose and ammonium chloride are weighed, and the mass ratio of glucose to ammonium chloride is 1:1. It is heated to 400 °C under an argon atmosphere, with a heating rate of 5 °C / min, and held for 3 hours. Then, it is heated to 1200 °C at a heating rate of 5 °C / min and carbonized for 5 h to obtain a graphene-like material. The graphene-like material, PVA, and the silicon / carbon / graphene material are mixed in a mass ratio of 7:2:91, and then heated to 500 °C under an argon atmosphere, with a heating rate of 5 °C / min, and held for 3 hours to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material.

[0091] The graphene-like carbon-coated silicon / carbon / graphene composite materials obtained from the above Examples 1 to 19, the silicon / carbon / graphene composite material obtained from Comparative Example 1, and the graphene-like carbon-coated silicon / carbon / graphene composite material obtained from Comparative Example 2 are used as working electrodes, lithium metal is used as the counter electrode, and the electrolyte is a common lithium-ion battery electrolyte to prepare 2032-type button cells. The discharge capacity after 100 cycles is tested at a current density of 0.1 A / g, and the test results are listed in Table 1.

[0092] Table 1

[0093]

[0094]

[0095] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0096] Graphene is considered an ideal composite matrix for the anode material of lithium-ion batteries due to its excellent properties: its large surface area can increase the storage density of lithium ions, good mechanical flexibility can effectively alleviate the structural changes during the electrochemical reaction process, and excellent electrical conductivity can ensure the minimum ohmic loss during the discharge and charge reactions of the anode. However, graphene is expensive. Therefore, in this application, graphene-like carbon-coated silicon / carbon / graphene is used to form a composite material. The cost of graphene-like is much lower than that of graphene. Therefore, using graphene-like to replace part of graphene as the coating material can reduce the cost of the composite material. When this composite material is used as the electrode of the battery, the cost can be greatly reduced, and large-scale production can be achieved. The nanosilicon in the graphene-like carbon-coated silicon / carbon / graphene composite material of this application is wrapped by a double carbon layer of graphene and graphene-like, which can effectively alleviate the volume effect of nanosilicon, thereby avoiding the direct contact between nanosilicon and the electrolyte, and further improving the cycle stability of the Si / C composite material. Moreover, this graphene-like carbon-coated silicon / carbon / graphene composite material has good electrical conductivity, high specific capacity, wide raw material sources, and is economical and environmentally friendly.

[0097] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A graphene-like carbon-coated silicon / carbon / graphene composite material, characterized in that, In terms of mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material comprises: 1-10% of a graphene-like carbon coating layer, 1-15% of silicon, 80-95% of carbon, and 0.1-5% of graphene; the thickness of the graphene-like carbon coating layer of the graphene-like carbon-coated silicon / carbon / graphene composite material is 5 nm; the graphene-like carbon coating layer is formed by heating and then calcining a mixture of a carbon source and a foaming agent in sequence.

2. The graphene-like carbon-coated silicon / carbon / graphene composite material according to claim 1, wherein The particle size of the graphene-like carbon-coated silicon / carbon / graphene composite material is 23-30 μm, and / or, in terms of mass percentage, the graphene-like carbon-coated silicon / carbon / graphene composite material comprises: 1-7% of a graphene-like carbon coating layer, 5-15% of silicon, 83-90% of carbon, and 0.1-3% of graphene.

3. A method for preparing a graphene-like carbon-coated silicon / carbon / graphene composite material according to claim 1 or 2, characterized in that, The preparation method comprises: Step S1, mixing a nano-silicon solution, a phenolic resin solution, a graphene slurry, and graphite to obtain a mixture; Step S2, drying the mixture to obtain a dried composite material powder; Step S3, in an inert atmosphere, heating a mixture of the dried composite material powder, a carbon source, and a foaming agent to obtain a carbon-coated composite material; and Step S4, calcining the carbon-coated composite material to obtain a graphene-like carbon-coated silicon / carbon / graphene composite material.

4. The preparation method according to claim 3, wherein In Step S3, the mass ratio of the dried composite material powder, the carbon source, and the foaming agent is 90-95:5-10:5-10, and / or, the carbon source is selected from any one or more of glucose, sucrose, and maltose, and / or, the foaming agent is selected from any one or more of ammonium chloride, ammonium sulfate, and ammonium carbonate.

5. The preparation method according to claim 3, characterized in that, In Step S3, the temperature of the heat treatment is 200-400 °C, and the time of the heat treatment is 1-5 h.

6. The preparation method according to claim 5, characterized in that, The temperature of the heat treatment is 250-400 °C, and the time of the heat treatment is 1-3 h.

7. The preparation method according to claim 3, characterized in that, In Step S4, the temperature of the calcination is 500-1500 °C, and the time of the calcination is 1-10 h.

8. The preparation method according to claim 7, characterized in that, The temperature of the calcination is 1200-1500 °C, and the time of the calcination is 5-10 h.

9. The preparation method according to claim 3, characterized in that, In Step S1, in terms of mass percentage, the dried composite material powder comprises 5-15% of nano-silicon, 1-4% of phenolic resin, 0.1-2% of graphene, and 80-90% of graphite.

10. The preparation method according to claim 9, characterized in that, The dried composite material powder comprises 8-12% of the nano-silicon, 2-3% of the phenolic resin, 0.2-1% of the graphene, and 84-89% of the graphite.

11. The preparation method according to claim 3, characterized in that, In Step S2, the drying is spray drying, and the temperature of the spray drying is 100-200 °C.

12. The preparation method according to claim 3, characterized in that, Before Step S1, the preparation method further comprises: Ball-milling a silicon source with a particle size of 100-200 μm in an organic solvent to obtain a nano-silicon solution.

13. The preparation method according to claim 12, wherein The silicon source is silicon powder, and / or the organic solvent is selected from any one or more of ethanol, ethylene glycol, and isopropanol, and / or the mass ratio of the grinding balls to the silicon source is 1.4 to 2.2:1, and / or the speed of the ball milling is 2000 rpm, and / or the time of the ball milling is 1 to 6 h.

14. The preparation method according to claim 13, wherein, The mass ratio of the grinding balls to the silicon source is 1.6 to 2.2:1, and / or the grinding balls are zirconia grinding balls, and the particle size of the zirconia grinding balls is 0.1 to 1 mm.

15. A negative electrode material, characterized in that, The negative electrode material includes the graphene-like carbon-coated silicon / carbon / graphene composite material described in any one of claims 1 or 2.

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