Graphene coated silicon carbon material and preparation method thereof

Abstract

The invention discloses a graphene coated silicon carbon material and a preparation method thereof. The preparation method comprises the following steps: step 01, modifying a silicon carbon material by adopting a surface modifier to obtain modified silicon carbon with positive charges on the surface; step 02, dispersing the modified silicon carbon in water to form a silicon carbon dispersion liquid, adding the graphene oxide dispersion liquid into the silicon carbon dispersion liquid, and carrying out blending and drying to obtain graphene oxide coated silicon carbon; and step 03, in an inert gas environment, carrying out heating reduction on the graphene oxide coated silicon carbon to obtain the graphene coated silicon carbon material. The graphene coated silicon carbon material prepared by the preparation method has excellent rate capability and cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and specifically relates to a graphene-coated silicon-carbon material and its preparation method. Background Technology

[0002] With the miniaturization and high performance of electronic devices and the rapid development of the electric vehicle industry, extremely stringent requirements have been placed on the energy density, cycle life, and charge / discharge rate of lithium-ion batteries. Silicon-based materials, with their theoretical specific capacity of up to 4200 mAh / g, far exceeding that of traditional graphite anode materials (theoretical specific capacity of approximately 372 mAh / g), have become highly promising next-generation lithium-ion battery anode materials. However, silicon undergoes a volume change of up to approximately 300% during lithium-ion insertion and extraction. This significant volume expansion and contraction leads to electrode material pulverization, disrupting the integrity of the electrode structure and causing rapid capacity decay, severely limiting the practical application of silicon-based materials.

[0003] To overcome the volume expansion problem of silicon, silicon-carbon composite materials have emerged. These materials utilize high-energy ball milling or sand milling processes to combine silicon particles with graphite microparticles, thus buffering the volume changes of silicon during charge and discharge. However, the buffering effect is limited. To further improve the overall performance of porous silicon-carbon anodes, numerous studies have focused on surface modification and optimization to constrain the volume changes of silicon-carbon composite materials during charge and discharge. For example, coating porous silicon-carbon with polymer coatings enhances the structural stability of the material to some extent, but its effect on improving the initial charge and discharge efficiency is minimal. Furthermore, due to the insulating properties of the polymer itself, it may increase the electrode resistance, negatively impacting the rate performance of the battery. Summary of the Invention

[0004] To address the aforementioned problems, this invention discloses a graphene-coated silicon-carbon material and its preparation method, in order to overcome or at least partially solve the aforementioned problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention discloses a method for preparing graphene-coated silicon-carbon material, the method comprising: Step 01: Modify silicon-carbon material with a surface modifier to obtain modified silicon-carbon with a positively charged surface; Step 02: Disperse the modified silicon carbon in water to form a silicon carbon dispersion, and add a graphene oxide dispersion to the silicon carbon dispersion. Then, after blending and drying, obtain graphene oxide-coated silicon carbon. Step 03: Under an inert gas environment, the graphene oxide-coated silicon carbon is heated and reduced to obtain a graphene-coated silicon carbon material.

[0006] Furthermore, the surface modifier is two or three of ammonia, polydimethylammonium chloride, and polyethyleneimine.

[0007] Furthermore, the mass ratio of the surface modifier to the silicon-carbon material is 0.1 to 1:1.

[0008] Further, step 01 includes: The surface modifier is dissolved in water to form a surface modifier solution with a mass concentration of 0.1-1%. Then, the silicon carbon material is added to the surface modifier solution and stirred continuously at a temperature of 20-30°C for 1-4 hours. The modified silicon carbon is then obtained by filtration or centrifugation.

[0009] Further, in step 02, the mass ratio of the modified silicon carbon to the graphene oxide is 1:0.01~0.1.

[0010] Furthermore, in step 02, the blending conditions are as follows: Stir continuously at 50-300 r / min for 30-180 min at room temperature.

[0011] Further, step 03 includes: Under a nitrogen flow rate of 1-10 L / min, the graphene oxide-coated silicon carbon is heated to 500-650°C and held at that temperature for 1-2 hours to obtain the graphene-coated silicon carbon material; or, Under a nitrogen flow rate of 1~10 L / min, the graphene oxide-coated silicon carbon is first heated to 300℃ at a heating rate of 0.1~1℃ / min and held at the temperature for 1~6h; finally, it is heated to 600℃ at a heating rate of 1~10℃ / min to obtain the graphene-coated silicon carbon material. Under a nitrogen flow rate of 1-10 L / min, the graphene oxide-coated silicon carbon is first heated to 120°C at a heating rate of 1-10°C / min and held at that temperature for 1-6 h; then heated to 150°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; then heated to 300°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; finally heated to 550°C at a heating rate of 1-5°C / min and held at that temperature for 1-2 h before cooling to room temperature to obtain the graphene-coated silicon carbon material.

[0012] Furthermore, the silicon-carbon material in step 01 is prepared by chemical vapor deposition.

[0013] Furthermore, the preparation process of the silicon-carbon material is as follows: First, the porous carbon material is placed in a tube furnace and replaced with an inert gas to reduce the oxygen content inside the furnace to less than 50 ppm. Next, the furnace is heated to 400-600°C at a rate of 1°C / min to 10°C / min and held for 30 minutes. Then, silicon source gas is introduced into the furnace at an average flow rate of 1 L / min, and the reaction proceeds for 40-80 minutes. The silicon source gas is then expelled from the furnace using an inert gas, and the furnace is heated to 500-550°C and held for 30 minutes. Finally, under inert gas protection, carbon source gas is introduced into the furnace at an average flow rate of 1 L / min, heating is stopped, and the furnace is cooled to room temperature.

[0014] Another aspect of the present invention discloses a graphene-coated silicon-carbon material, which is prepared by the above-described method for preparing graphene-coated silicon-carbon material.

[0015] The advantages and beneficial effects of this invention are: In the preparation method of this invention, the surface of silicon-carbon material is first modified with a positive charge, and the electrostatic attraction is cleverly used to achieve a tight coating of silicon-carbon material with graphene oxide, which makes the coating more uniform and stable, laying a solid foundation for the subsequent uniform coating of graphene. Then, the graphene oxide coated on the silicon-carbon material is reduced to graphene through a reduction reaction, thereby forming a graphene coating layer on the surface of the silicon-carbon material. Due to the excellent conductivity of graphene, the graphene coating layer can build a fast channel for electron transport, significantly improving the rate performance of the material. Furthermore, based on the excellent mechanical properties of graphene, it can better buffer the volume change of silicon during charging and discharging, effectively reducing the pulverization and structural damage of the electrode material, thereby significantly improving the cycle stability of silicon-carbon material as an electrode material. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a flowchart illustrating the steps of a method for preparing graphene-coated silicon-carbon material in one embodiment of the present invention. Figure 2 The graph shows the cycle capacity and capacity retention of the material samples prepared in Example 1 and Comparative Example 2 during coin cell cycle testing at a current density of 0.5C. Figure 3 SEM image of silicon-carbon material; Figure 4 SEM image of silicon-carbon material coated with graphene; Figure 5 SEM images of the material sample prepared for Comparative Example 3; Figure 6 The graph shows the Zeta potential of surface modifiers and silicon-carbon materials with different addition amounts. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more complete description will be provided below. Preferred embodiments of the invention are given below. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0019] This document refers to numerical ranges, which, unless otherwise specified, are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between them. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0020] Unless otherwise specified, the temperature parameters in this document can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] One embodiment of the present invention provides a method for preparing graphene-coated silicon-carbon material, such as... Figure 1 As shown, the preparation method includes: Step 01 involves modifying the silicon-carbon material with a surface modifier to obtain modified silicon-carbon with a stronger positive surface charge. The silicon-carbon material is a composite structure formed by combining silicon (Si) as the main active material with carbon materials (such as graphite, carbon nanotubes, and graphene). The surface modifier is specifically two or three of the following: ammonia, polydimethylammonium chloride, and polyethyleneimine.

[0023] Understandably, modifying the surface of silicon-carbon materials with surface modifiers introduces a positive charge, significantly enhancing the positive charge on the surface. This allows the silicon-carbon surface to tightly bond with negatively charged graphene oxide through electrostatic interactions in subsequent steps, creating conditions for uniform coating. For example, surface modifiers such as polydienepropylene dimethyl ammonium chloride or polyethyleneimine ionize or protonate in water, thus giving the molecules or molecular chains a positive charge. The rich surface microstructure of the silicon-carbon particles adsorbs and self-assembles, resulting in modified silicon-carbon with a stronger positive charge on the surface.

[0024] Step 02: Disperse modified silicon carbon in water to form a silicon carbon dispersion, add graphene oxide dispersion to the silicon carbon dispersion, and then mix and dry to obtain graphene oxide coated silicon carbon.

[0025] Specifically, graphene oxide prepared by the Hummers method (this preparation method is just an example and not a limitation on the preparation method of graphene oxide) is dispersed in deionized water by slow dropwise addition. The mixture is stirred continuously at a stirring speed of 240 r / min for 30 to 180 min to obtain a graphene oxide dispersion. Then, a silicon carbon dispersion is added to the graphene oxide dispersion, and the mixture is stirred continuously at a stirring speed of 240 r / min for 30 to 180 min at room temperature. Co-precipitation occurs in the solution, thus completing the coating.

[0026] Understandably, in a solution environment, positively charged silicon-carbon materials can tightly bind with negatively charged graphene oxide, achieving graphene oxide coating through electrostatic adsorption. This results in higher uniformity and stability of the coating, forming a tightly bound graphene oxide-coated silicon-carbon structure after drying. Furthermore, during thermal reduction, this electrostatic adsorption ensures the graphene-coated silicon-carbon material maintains good structural stability, effectively preventing the separation of the graphene coating layer during charging and discharging, thus ensuring the reliability and stability of the material's performance.

[0027] Step 03: Under an inert gas environment, graphene oxide coated silicon carbon is heated and reduced to obtain graphene-coated silicon carbon material.

[0028] Graphene oxide was selected as a precursor for graphene. After it was tightly bonded to silicon-carbon materials, the oxygen-containing functional groups on the surface of the graphene oxide were removed through a reduction reaction, converting the graphene oxide into graphene. This successfully constructed a graphene coating layer with excellent performance on the surface of the silicon-carbon materials. Based on graphene's excellent electrical and mechanical properties, its high conductivity helps improve the rate performance of the material, while its outstanding mechanical properties can buffer the volume change of silicon to a certain extent, significantly improving cycle stability.

[0029] In summary, the preparation method of this embodiment first modifies the surface of silicon-carbon material with positive charge, cleverly utilizing electrostatic attraction to achieve a tight coating of silicon-carbon material with graphene oxide, resulting in higher uniformity and stability of the coating and laying a solid foundation for subsequent uniform graphene coating. Then, the graphene oxide coated on the silicon-carbon material is reduced to graphene through a reduction reaction, thereby constructing a graphene coating layer on the surface of the silicon-carbon material. Due to the excellent conductivity of graphene, the graphene coating layer can build a fast channel for electron transport, significantly improving the rate performance of the material. Furthermore, based on the excellent mechanical properties of graphene, it can better buffer the volume change of silicon during charging and discharging, effectively reducing the pulverization and structural damage of the electrode material, thereby significantly improving the cycle stability of silicon-carbon material as an electrode material.

[0030] In this embodiment, the mass ratio of the surface modifier to the silicon-carbon material is 0.1 to 1:1. Figure 6 As can be seen, after surface treatment, the Zeta potential of the silicon-carbon material increases with the increase of the amount of surface modifier added. When the amount added in water exceeds 750 mg / 100 ml, the increasing trend of the Zeta potential of the silicon-carbon particles slows down. In this embodiment, the mass ratio of surface modifier to silicon-carbon material is set to 0.1~1:1, which can ensure that the surface of the silicon-carbon material is completely modified while taking into account economic benefits.

[0031] Additionally, step 01 includes: A surface modifier is dissolved in water to form a surface modifier solution with a mass concentration of 0.1-1%. The silicon-carbon material is then added to the surface modifier solution, and the mixture is stirred continuously at 20-30°C for 1-4 hours. The modified silicon-carbon is then obtained by filtration or centrifugation. This process ensures that the surface of the silicon-carbon material is completely modified, resulting in a greater amount of positive charge generated on the material.

[0032] In addition, in step 02, the mass ratio of modified silicon carbon to graphene oxide is 1:0.01~0.1.

[0033] Too low a graphene oxide addition amount cannot form an effective coating on the modified silicon carbon, resulting in a large amount of silicon carbon residue in the supernatant after coprecipitation. On the other hand, too high a graphene oxide addition amount results in a large amount of residual graphene oxide in the supernatant after coprecipitation, which has a significant impact on the electrode energy density.

[0034] In this embodiment, the silicon-carbon material in step 01 is prepared by chemical vapor deposition. The silicon-carbon material prepared by chemical vapor deposition not only has high purity and high crystallinity, but also good compositional uniformity and structural density.

[0035] Furthermore, in the process of preparing silicon-carbon materials by chemical vapor deposition, high-temperature pyrolysis of silane gas enables the directional deposition of nanoscale silicon particles on the surface and within the pores of a porous carbon substrate. The three-dimensional network structure of porous carbon provides expansion buffer space for silicon particles, effectively suppressing the 300% volume expansion effect during charging and discharging.

[0036] Furthermore, the specific preparation process of silicon-carbon materials is as follows: First, porous carbon material is placed in a tube furnace and purged with inert gas to reduce the oxygen content inside the furnace to less than 50 ppm. Next, the furnace is heated to 400-600°C at a rate of 1-10°C / min and held for 30 minutes. Then, silicon source gas is introduced into the furnace at an average flow rate of 1 L / min, and the reaction proceeds for 40-80 minutes. The silicon source gas is then expelled from the furnace using inert gas, and the furnace is heated to 500-550°C and held for 30 minutes. Finally, under inert gas protection, carbon source gas is introduced into the furnace at an average flow rate of 1 L / min, heating is stopped, and the furnace is cooled to room temperature. The purpose of the furnace's temperature control and the control of the carbon source flow rate is to achieve uniform deposition of silicon particles. The deposition temperature of 400-600°C is to prevent excessively high temperatures from causing carbonization reactions between the silicon particles, the carbon source, and the carbon support, which would affect the capacitance.

[0037] The inert gas is argon or nitrogen. The silicon source gas is one or more combinations of silane, ethane, and propane; the carbon source gas is one or more combinations of ethylene, acetylene, and propylene.

[0038] In this embodiment, the silicon carbon dispersion was added to the graphene oxide dispersion, and the solution was continuously stirred at 240 r / min for 30 to 180 min at room temperature to achieve solution blending.

[0039] Understandably, stirring at room temperature can effectively prevent the swelling and thickening of graphene oxide. The purpose of continuous and rapid stirring is to promote the full mixing of modified silicon carbon and graphene oxide, which is beneficial to the uniformity of coating.

[0040] In addition, after the silicon carbon dispersion and the graphene oxide dispersion were blended, the mixture underwent co-precipitation, which completed the coating. After standing for 30 minutes, the precipitate was removed by vacuum filtration. The silicon carbon dispersion coated with graphene oxide was then dried to obtain silicon carbon coated with graphene oxide, which was prepared for the subsequent reduction reaction.

[0041] Among them, the co-precipitation behavior of modified silicon carbon and graphene oxide during the mixing process is conducive to the rapid separation of the coated product from the solution, that is, graphene oxide coated silicon carbon can be obtained by simply using a vacuum filtration process.

[0042] In other embodiments, in step 02, after the silicon carbon dispersion and the graphene oxide dispersion are blended, the blend is dried by stirring. Specifically, the stirring speed is 100 rpm and the stirring temperature is 90~120℃.

[0043] When preparing silicon-carbon using CVD (chemical vapor deposition), silicon nanoparticles are deposited on the surface of a carbon substrate (such as carbon nanotubes or graphite) using a gaseous silicon source (such as silane). During this process, the accumulation of silicon particles easily leads to the formation of porous structures or gaps (especially in high-silicon content systems). The presence of these pores results in: a significant increase in specific surface area (exposing more active surfaces); and the electrolyte easily penetrating deep into the pores, exacerbating side reactions.

[0044] During the stirring and drying process, the sheet-like structure of graphene can adhere to the surface of silicon carbon through van der Waals forces or physical adsorption, covering and sealing these open pores, thereby greatly reducing the specific surface area and further isolating the electrolyte from direct contact with silicon carbon, thus reducing the thickness of the SEI film (solid electrolyte interface).

[0045] In another embodiment of the present invention, step 02 further includes: Graphene oxide-coated silicon carbon is dispersed in a graphene oxide dispersion and a hydrogel is formed through a hydrothermal reaction. The hydrogel is then dried to obtain re-coated graphene oxide-coated silicon carbon.

[0046] Specifically, the prepared graphene-coated silicon carbon is dispersed in a graphene oxide dispersion and stirred continuously for 1-2 hours to ensure that the graphene-coated silicon carbon is fully dispersed in the graphene oxide dispersion. Then, the dispersion is placed in a hydrothermal reactor for hydrothermal reaction to form a hydrogel. The hydrogel is dried to obtain the re-coated graphene-coated silicon carbon.

[0047] Understandably, when graphene oxide in a graphene oxide dispersion is heated, most of the oxidized functional groups of the graphene oxide will be reduced and removed, forming a hydrogel. During subsequent drying, the capillary force generated by the surface tension of water causes the pore structure of the hydrogel to collapse, forcibly adhering the graphene oxide to the graphene oxide-coated silicon carbon, achieving a secondary coating effect of graphene oxide. This significantly improves the integrity of the graphene oxide-coated silicon carbon material. In this embodiment, a primary coating of silicon carbon with graphene oxide is formed by solution stirring, and a secondary coating is formed by hydrothermal methods. This ensures that the graphene is fully coated on the silicon carbon, not only improving the integrity of the graphene-coated silicon carbon and effectively isolating the silicon-based anode from direct contact with the battery electrolyte, thus reducing the thickness of the solid electrolyte interface film, but also improving the mechanical strength of the graphene coating layer. This allows the graphene coating layer to maintain its structural integrity during the charging and discharging process of the silicon carbon anode, thereby preventing the graphene coating layer from cracking due to volume changes in the silicon carbon anode.

[0048] In this embodiment, step 03 includes: Graphene oxide coated silicon carbon was heated to 500-650℃ and held at the temperature for 1-2 hours under a nitrogen flow rate of 1-10 L / min to obtain graphene-coated silicon carbon material.

[0049] Understandably, too low a nitrogen flow rate will result in residual oxygen, while too high a nitrogen flow rate will affect heat preservation and cause waste. Furthermore, too low a heating temperature for graphene oxide coated with silicon carbon is not conducive to the reduction of graphene oxide, while too high a heating temperature will lead to the carbonization of silicon particles.

[0050] In other embodiments, step 03 includes: Under a nitrogen flow rate of 1~10 L / min, graphene oxide coated silicon carbon is first heated to 300℃ at a heating rate of 0.1~1℃ / min and held at the temperature for 1~6h; finally, it is heated to 600℃ at a heating rate of 1~10℃ / min and held at the temperature for 1~2h to obtain graphene coated silicon carbon material.

[0051] The process employs a two-stage heating method: first, slow processing at a low temperature (300℃), followed by graphitization at a high temperature (600℃). This step-by-step approach addresses the needs for "functional group removal" and "structural stability," avoiding structural damage caused by a single high-temperature step. Specifically, the low-temperature stage is the "preliminary reduction and pretreatment" stage for graphene oxide, aiming to "gently remove oxygen-containing functional groups from graphene oxide and alleviate thermal stress on silicon-carbon." The high-temperature stage is the "deep graphitization and interface bonding strengthening" stage for graphene, aiming to "improve the conductivity of graphitization and ensure a tight bond between the graphitized layer and the silicon-carbon matrix."

[0052] Alternatively, step 03 may include: Under a nitrogen flow rate of 1-10 L / min, graphene oxide coated silicon carbon was first heated to 120°C at a heating rate of 1-10°C / min and held at that temperature for 1-6 h; then heated to 150°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; then heated to 300°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; finally heated to 550°C at a heating rate of 1-5°C / min and held at that temperature for 1-2 h before cooling to room temperature to obtain graphene-coated silicon carbon material.

[0053] Understandably, during the thermal reduction of graphene oxide coated on silicon-carbon materials, gas is generated due to the removal of functional groups. If the temperature rises too quickly during heating, excessive gas production will occur instantaneously, causing the coated graphene to expand and affecting the integrity of the graphene coating. Therefore, this embodiment employs a stepped heating method to reduce graphene oxide. Specifically, firstly, the graphene oxide coated on silicon-carbon is heated to 120°C at a heating rate of 1–10°C / min and held for 1–6 hours. At around 120°C, the primarily physical adsorption of water is removed. Secondly, the graphene oxide coated on silicon-carbon is heated to 150°C at a heating rate of 0.1–0.5°C / min and held for 1–6 hours to specifically remove weakly bound oxygen-containing functional groups (such as hydroxyl and some epoxy groups). At this stage, gas release is minimal, and localized stress concentration is avoided. Finally, the heating rate is increased to 0.1–0.5°C / min... The coating material is heated to 300℃ to deeply remove "strongly bound oxygen-containing functional groups" (such as carboxyl groups and residual epoxy groups), while simultaneously repairing some carbon skeleton defects. Finally, the coating material is heated to 550℃ at a heating rate of 1~5℃ / min and held at that temperature for 1~2 hours. Since most of the oxidized functional groups have been removed after 300℃, the temperature can be rapidly increased to 550℃ to completely remove the remaining small number of functional groups and stubborn impurities, and further graphitize (improving the order of the carbon skeleton), ultimately forming reduced graphene oxide.

[0054] In another embodiment of the present invention, a graphene-coated silicon-carbon material is provided, which is prepared using the preparation method described in the above embodiments. This graphene-coated silicon-carbon material exhibits excellent rate performance and cycle performance.

[0055] Example 1 First, 1 g of silicon carbon material was added to 100 ml of a surface modifier solution containing ammonia, polydimethylammonium chloride and polyethyleneimine, and the concentration of the surface modifier solution was prepared to be 0.75%. The mixture was stirred continuously at 240 r / min for 3 h at 25 °C. The modified silicon carbon was separated from the solution by vacuum filtration, and the modified silicon carbon was dispersed in 100 ml of water to form a silicon carbon dispersion.

[0056] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0057] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0058] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h; finally, it was heated to 600 ℃ at a heating rate of 2 ℃ / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0059] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0060] Example 2 First, 1 g of silicon carbon material was added to 100 ml of a surface modifier solution containing ammonia, polydipropylene dimethyl ammonium chloride, and polyethyleneimine, to prepare a surface modifier solution with a concentration of 0.1%. The solution was stirred continuously at 240 r / min for 3 h at 25 °C. The modified silicon carbon was separated from the solution by filtration, and the modified silicon carbon was dispersed in 100 ml of water to form a silicon carbon dispersion.

[0061] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0062] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0063] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h; finally, it was heated to 600 ℃ at a heating rate of 2 ℃ / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0064] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0065] Example 3 First, 1 g of silicon carbon material was added to 100 ml of a surface modifier solution containing ammonia, polydipropylene dimethyl ammonium chloride, and polyethyleneimine, to prepare a surface modifier solution with a concentration of 1%. The solution was stirred continuously at 240 r / min for 3 h at 25°C. The modified silicon carbon was separated from the solution by filtration, and the modified silicon carbon was dispersed in 100 ml of water to form a silicon carbon dispersion.

[0066] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0067] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0068] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h; finally, it was heated to 600 ℃ at a heating rate of 2 ℃ / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0069] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0070] Comparative Example 1 First, 1 g of silicon carbon material was added to 100 ml of deionized water and stirred continuously at 240 r / min for 3 h at 25°C. The silicon carbon material was separated from the solution by filtration and dispersed in 100 ml of water to form a silicon carbon dispersion.

[0071] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0072] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0073] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h; finally, it was heated to 600 ℃ at a heating rate of 2 ℃ / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0074] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0075] Comparative Example 2 Preparation of coin cells: Silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half cell for cycle and rate testing.

[0076] Comparative Example 3 First, 1 g of silicon carbon material was added to 100 ml of a surface modifier solution containing ammonia, polydipropylene dimethyl ammonium chloride, and polyethyleneimine, to prepare a surface modifier solution with a concentration of 0.75%. The solution was stirred continuously at 240 r / min for 3 h at 25 °C. The modified silicon carbon was separated from the solution by filtration, and the modified silicon carbon was dispersed in 100 ml of water to form a silicon carbon dispersion.

[0077] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0078] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0079] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 °C at a heating rate of 5 °C / min and held at that temperature for 1 h; finally, it was heated to 600 °C at a heating rate of 5 °C / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0080] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0081] Comparative Example 4 First, 1 g of silicon carbon material was added to 100 ml of a surface modifier solution containing ammonia, polydipropylene dimethyl ammonium chloride, and polyethyleneimine, to prepare a surface modifier solution with a concentration of 0.75%. The solution was stirred continuously at 240 r / min for 3 h at 25 °C. The modified silicon carbon was separated from the solution by filtration, and the modified silicon carbon was dispersed in 100 ml of water to form a silicon carbon dispersion.

[0082] Then, 0.1 g of graphene oxide prepared by the Hummers method was dispersed in deionized water by slow dropwise addition to form 100 ml of graphene oxide dispersion, and stirred continuously at a stirring speed of 240 r / min for 60 min.

[0083] The silicon carbon dispersion was then added to the graphene oxide dispersion. The mixture was stirred continuously at 240 r / min for 60 min at room temperature until co-precipitation occurred, thus completing the coating process. After standing for 30 min, the precipitate was removed by vacuum filtration. The graphene oxide-coated silicon carbon dispersion was then dried to obtain graphene oxide-coated silicon carbon.

[0084] Under a nitrogen flow rate of 3 L / min, graphene oxide-coated silicon carbon was first heated to 300 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h; finally, it was heated to 600 ℃ at a heating rate of 0.5 ℃ / min and held at that temperature for 1 h to obtain graphene-coated silicon carbon material (material sample).

[0085] Preparation of coin cells: Graphene-coated silicon-carbon material (material sample) is mixed with conductive agent and binder into a slurry, coated, and then made into a lithium half-cell for cycle and rate testing.

[0086] Table 1

[0087] The test results for each embodiment and comparative example are shown in Table 1. From Table 1 and... Figure 2 As can be seen, after 50 charge-discharge cycles, the material sample prepared by the method of this invention retains over 70% of its capacity, with a capacity of over 200 mAh / g. In contrast, the material sample without surface modification retains over 40% of its capacity, with a capacity of over 100 mAh / g, and the material sample without graphene coating retains only over 20% of its capacity, with a capacity of only over 100 mAh / g. This indicates that the material sample prepared by the method of this invention has excellent cycle stability. For Examples 1 to 3, Example 1 achieved the best performance, and the segmented heating process improved efficiency while ensuring coating stability. Comparative Example 1, which involves direct coating with graphene oxide without the addition of a modifier, shows a smaller performance improvement compared to Example 1. The sample in Comparative Example 3 adopted a rapid heating reduction strategy after coating, which led to the shedding and aggregation of graphene oxide during the reduction process, thus affecting the performance improvement. Compared with Example 1, Comparative Example 4 adopted a lower heating rate throughout the process, which also achieved a good performance improvement, but the heating time was longer and the efficiency was lower.

[0088] Figure 3 The image shows a SEM image of the uncoated silicon-carbon material. As can be seen from the image, the uncoated silicon-carbon material has a relatively smooth surface. Figure 4 The image shows a SEM image of silicon-carbon material coated with graphene. As can be seen from the image, the reduced graphene is uniformly coated on the surface of silicon-carbon. Figure 5 The image shows the morphology of the graphene-coated silicon-carbon material prepared in Comparative Example 3. Compared with Example 2, the graphene oxide reduction reaction is more intense due to the faster heating rate in Comparative Example 3, resulting in a greater tendency for graphene to detach and aggregate.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing graphene-coated silicon-carbon material, characterized in that, The preparation method includes: Step 01: Modify silicon-carbon material with a surface modifier to obtain modified silicon-carbon with a positively charged surface; Step 02: Disperse the modified silicon carbon in water to form a silicon carbon dispersion, and add a graphene oxide dispersion to the silicon carbon dispersion. Then, after blending and drying, obtain graphene oxide-coated silicon carbon. Step 03: Under an inert gas environment, the graphene oxide-coated silicon carbon is heated and reduced to obtain a graphene-coated silicon carbon material.

2. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, The surface modifier is two or three of the following: ammonia, polydimethylammonium chloride, and polyethyleneimine.

3. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, The mass ratio of the surface modifier to the silicon-carbon material is 0.1 to 1:

1.

4. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, Step 01 includes: The surface modifier is dissolved in water to form a surface modifier solution with a mass concentration of 0.1-1%. Then, the silicon carbon material is added to the surface modifier solution and stirred continuously at a temperature of 20-30°C for 1-4 hours. The modified silicon carbon is then obtained by filtration or centrifugation.

5. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 02, the mass ratio of the modified silicon carbon to the graphene oxide is 1:0.01~0.

1.

6. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 02, the blending conditions are as follows: Stir continuously at 50-300 r / min for 30-180 min at room temperature.

7. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, Step 03 includes: Under a nitrogen flow rate of 1-10 L / min, the graphene oxide-coated silicon carbon is heated to 500-650°C and held at that temperature for 1-2 hours to obtain the graphene-coated silicon carbon material; or, Under a nitrogen flow rate of 1-10 L / min, the graphene oxide-coated silicon carbon is first heated to 300°C at a heating rate of 0.1-1°C / min and held at that temperature for 1-6 hours; finally, it is heated to 600°C at a heating rate of 1-10°C / min to obtain the graphene-coated silicon carbon material; or, Under a nitrogen flow rate of 1-10 L / min, the graphene oxide-coated silicon carbon is first heated to 120°C at a heating rate of 1-10°C / min and held at that temperature for 1-6 h; then heated to 150°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; then heated to 300°C at a heating rate of 0.1-0.5°C / min and held at that temperature for 1-6 h; finally heated to 550°C at a heating rate of 1-5°C / min and held at that temperature for 1-2 h before cooling to room temperature to obtain the graphene-coated silicon carbon material.

8. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, The silicon-carbon material in step 01 is prepared by chemical vapor deposition.

9. The method for preparing graphene-coated silicon-carbon material according to claim 8, characterized in that, The specific preparation process of the silicon-carbon material is as follows: First, the porous carbon material is placed in a tube furnace and replaced with an inert gas to reduce the oxygen content inside the furnace to less than 50 ppm. Next, the furnace is heated to 400-600°C at a rate of 1°C / min to 10°C / min and held for 30 minutes. Then, silicon source gas is introduced into the furnace at an average flow rate of 1 L / min, and the reaction proceeds for 40-80 minutes. The silicon source gas is then expelled from the furnace using an inert gas, and the furnace is heated to 500-550°C and held for 30 minutes. Finally, under inert gas protection, carbon source gas is introduced into the furnace at an average flow rate of 1 L / min, heating is stopped, and the furnace is cooled to room temperature.

10. A graphene-coated silicon-carbon material, characterized in that, The graphene-coated silicon-carbon material is prepared using the preparation method of graphene-coated silicon-carbon material according to any one of claims 1 to 9.

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