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, surface modification: modifying a silicon carbon material by adopting a surface modifier to obtain modified silicon carbon; 02, primary coating: dispersing the modified silicon carbon in water to form a silicon carbon dispersion liquid, adding a graphene oxide dispersion liquid into the silicon carbon dispersion liquid until the dispersion liquid is slightly yellow, and then filtering and drying to obtain a primary coating material; step 03, secondary coating: dispersing the primary coating material in a graphene oxide dispersion liquid, forming hydrogel through a hydrothermal reaction, and drying the hydrogel to obtain a secondary coating material; and step 04, thermal reduction treatment: carrying out heating reduction on the secondary coating material to obtain the graphene-coated silicon carbon material. According to the preparation method, not only is the integrity of the graphene coated silicon carbon improved, but also the mechanical strength of the graphene coating layer is improved, and the situation that the graphene coating layer is cracked due to the volume change of the silicon carbon is effectively prevented.

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] In recent years, the rapid consumption of fossil fuels has led to increasingly prominent environmental pollution and global warming problems, resulting in frequent extreme weather events such as heat waves and torrential rains. In response, the international community has reached a consensus on environmental protection, making the transition to a sustainable energy economy and a low-carbon future imperative. Lithium-ion batteries, with their clean and reliable characteristics, are widely used in portable electronic products, electric vehicles, and many other fields. Currently, most lithium-ion batteries use graphite as the anode material, but the theoretical specific capacity of commercially available graphite is only 372 mAh·g. -1 This results in poor energy density, power density, and cycle stability of lithium-ion batteries, making it difficult to meet the needs of large-scale applications.

[0003] Due to silicon's theoretical specific capacity of up to 4200 mAh g -1 (Based on the formation of the lithium-silicon alloy Li4.4Si), it is more than 10 times that of traditional graphite anodes. Under the same mass, silicon-based anodes can store more lithium ions, directly increasing the battery's energy density (energy per unit mass / volume). Furthermore, silicon is abundant in the Earth's crust and has environmental advantages, making it a highly sought-after electrode material. However, during the lithium storage process (forming Li4.4Si), silicon... x Silicon alloys (Si alloys) can experience a volume expansion of 300%-400%, which can easily lead to electrode pulverization and detachment of active materials. Graphene, with its excellent flexibility and elasticity, can encapsulate silicon particles like an "elastic jacket," buffering stress through its own deformation during silicon expansion, inhibiting particle agglomeration and electrode cracking, and significantly improving cycle stability.

[0004] Currently, the common method is to first use a solution stirring method to form graphene oxide coating on the silicon-based anode, and then reduce the graphene oxide back to graphene to finally achieve graphene coating on the silicon-based anode. However, this method makes it difficult to ensure that the surface of the silicon-based anode is completely coated, resulting in rapid reversible capacity decay of the assembled coin cells during cycle testing. Furthermore, the graphene coating layer formed by this method has poor structural strength, and the volume change of the silicon-based anode during charge and discharge can easily cause the graphene coating layer to crack, seriously affecting the battery life. Summary of the Invention

[0005] 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.

[0006] 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, Surface modification: The silicon-carbon material is modified with a surface modifier to obtain modified silicon-carbon; Step 02, primary coating: The modified silicon carbon is dispersed in water to form a silicon carbon dispersion, and graphene oxide dispersion is added to the silicon carbon dispersion until the dispersion turns slightly yellow. Then, the mixture is filtered and dried to obtain the primary coating material. Step 03, Secondary Coating: The primary coating material is dispersed in a graphene oxide dispersion and a hydrogel is formed through a hydrothermal reaction. The hydrogel is then dried to obtain the secondary coating material. Step 04, thermal reduction treatment: The secondary coating material is heated and reduced to obtain graphene-coated silicon carbon material.

[0007] Furthermore, in step 04, the heating method for the secondary coating material is a stepped heating method.

[0008] Furthermore, the secondary coating material is first heated to 120°C at a heating rate of 1~10°C / min and held at that temperature for 1~6 hours; then heated to 150°C at a heating rate of 0.1~0.5°C / min and held at that temperature for 1~6 hours; then heated to 300°C at a heating rate of 0.1~0.5°C / min; and finally heated to 550°C at a heating rate of 1~5°C / min and held at that temperature for 1~2 hours before being cooled to room temperature.

[0009] Furthermore, in step 01, the mass ratio of silicon-carbon material to surface modifier is 1:1 to 1:2.

[0010] Furthermore, the surface modifier is one or more of polyethyleneimine, polylysine, polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, hexadecyltrimethylammonium bromide, and polydopamine.

[0011] Further, step 01 includes: First, the silicon-carbon material is dispersed in water to form a silicon-carbon material dispersion with a concentration of 1% to 10%. Then, the surface modifier is added to the silicon-carbon material dispersion and stirred thoroughly at a speed of 200 to 400 rpm for 3 to 5 hours. Finally, the modified silicon-carbon is obtained by centrifugation or filtration and drying.

[0012] Furthermore, in step 02, the mass ratio of modified silicon carbon to water in the silicon carbon dispersion is 1:100~200, and the solid fraction of the graphene oxide dispersion is 0.90%~0.92%.

[0013] Furthermore, in step 03, the mass ratio of the primary coating material to graphene oxide is 100:1~7.

[0014] Furthermore, in step 03, the solid fraction of the graphene oxide dispersion is 0.1% to 0.2%.

[0015] Furthermore, in step 03, the hydrothermal reaction conditions are: reacting at a temperature of 120℃~150℃ for 5~7 hours.

[0016] Furthermore, in step 03, the drying temperature is 90℃~120℃, and the drying time is 8~12h.

[0017] Furthermore, the silicon-carbon material in step 01 is prepared by chemical vapor deposition.

[0018] 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. Then, the furnace is heated to 400-600°C at a heating rate of 1°C / min to 10°C / min and held for 30 min. Next, silicon source gas is introduced into the furnace at an average flow rate of 1 L / min, and the reaction is allowed to proceed for 40-80 min. Then, the silicon source gas is expelled from the furnace using an inert gas, and the furnace is heated to 500-550°C and held for 30 min. 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.

[0019] 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.

[0020] The advantages and beneficial effects of this invention are: In the preparation method of graphene-coated silicon-carbon material of the present invention, a primary coating of silicon-carbon is formed by solution stirring, and a secondary coating of silicon-carbon is formed by hydrothermal method. This allows graphene to be fully coated on silicon-carbon, which not only improves the integrity of graphene-coated silicon-carbon and effectively isolates the direct contact between the silicon-based anode and the battery electrolyte, thereby reducing the thickness of the solid electrolyte interface film, but also improves 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, thus avoiding the cracking of the graphene coating layer caused by the volume change of the silicon-carbon anode. Furthermore, the graphene-coated silicon-carbon material prepared by this method has excellent cycle performance. Attached Figure Description

[0021] 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 Cyclic capacity diagrams of material samples prepared for each embodiment and comparative example under coin cell cycle testing at a current density of 0.3C; Figure 3 The capacity retention graphs of the material samples prepared in each embodiment and comparative example during coin cell cycle testing are shown. Figure 4 The image shows the SEM characterization of the material sample in Example 1. Figure 5 The image shows the SEM characterization of the material sample in Comparative Example 1. Figure 6 The image shows the SEM characterization of the material sample in Comparative Example 2. Figure 7 The image shows the SEM characterization of the material sample in Comparative Example 3. Figure 8 The image shows the SEM characterization of the material sample in Comparative Example 4. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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, Surface Modification: Silicon-carbon materials are modified using surface modifiers to obtain modified silicon-carbon. 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, graphene, etc.). The surface modifier is one or more of the following: polyethyleneimine, polylysine, polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, hexadecyltrimethylammonium bromide, and polydopamine.

[0028] Understandably, modifying silicon-carbon materials with surface modifiers transforms the surface charge into a positive charge, thus positively modifying the surface to facilitate subsequent electrostatic adsorption of graphene oxide. Furthermore, during thermal reduction, this process maintains the good structural stability of the graphene-coated silicon-carbon material, effectively preventing the separation of the graphene coating during charging and discharging, and ensuring the reliability and stability of the material's performance.

[0029] Step 02, Primary Coating: The modified silicon carbon is dispersed in water to form a silicon carbon dispersion. A graphene oxide dispersion is then added to the silicon carbon dispersion until it turns slightly yellow. The mixture is then filtered and dried to obtain the primary coated material. The slight yellowing of the dispersion indicates a slight excess of graphene oxide, signifying that the graphene oxide has completed the primary coating of the modified silicon carbon.

[0030] Understandably, when silicon carbon materials are modified with surface modifiers to obtain positively charged modified silicon carbon, and then the modified silicon carbon is placed in a graphene oxide dispersion, the graphene oxide, which has a negative charge on its surface, can automatically coat the modified silicon carbon under the attraction of positive and negative charges, achieving a one-time coating with higher uniformity and stability.

[0031] Step 03, Secondary Coating: Disperse the primary coating material in the graphene oxide dispersion and stir continuously for 1-2 hours to ensure that the primary coating material is fully dispersed in the graphene oxide dispersion; then place the dispersion in a hydrothermal reactor to carry out a hydrothermal reaction to form a hydrogel, and dry the hydrogel to obtain the secondary coating material.

[0032] 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, thereby forcibly adhering the graphene oxide to the primary coating material, achieving a secondary coating effect. This can greatly improve the integrity of the graphene oxide coating on silicon carbon materials.

[0033] Step 04, thermal reduction treatment: The secondary coating material is heated and reduced to reduce graphene oxide to graphene, thereby obtaining graphene-coated silicon carbon material.

[0034] After obtaining graphene-coated silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain finished powder material.

[0035] In summary, the preparation method in this embodiment involves a primary coating of silicon-carbon using a solution stirring method and a secondary coating using a hydrothermal method. This ensures that graphene is fully coated onto the silicon-carbon, improving the integrity of the graphene-coated silicon-carbon structure, effectively isolating the silicon-based anode from direct contact with the battery electrolyte, and thus reducing the thickness of the solid electrolyte interface film. Furthermore, it enhances the mechanical strength of the graphene coating, enabling it to maintain structural integrity during the charging and discharging process of the silicon-carbon anode, thereby preventing cracking of the graphene coating due to volume changes in the silicon-carbon anode. Moreover, the graphene-coated silicon-carbon material prepared by this method exhibits excellent cycle performance.

[0036] In this embodiment, in step 04, the heating method for the secondary coating material is stepped heating.

[0037] The stepped heating process is as follows: the secondary coating material is first heated to 120℃ at a heating rate of 1~10℃ / min and held at that temperature for 1~6h; then heated to 150℃ at a heating rate of 0.1~0.5℃ / min and held at that temperature for 1~6h; then heated to 300℃ at a heating rate of 0.1~0.5℃ / min and held at that temperature for 1~6h; finally heated to 550℃ at a heating rate of 1~5℃ / min and held at that temperature for 1~2h before cooling to room temperature.

[0038] 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 secondary coating material 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 physically adsorbed water is primarily removed. Secondly, the secondary coating material 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. Then, the coating material is heated to 150°C at a heating rate of 0.1–0.5°C / min. The 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.

[0039] Furthermore, in step 01, the mass ratio of silicon-carbon material to surface modifier is 1:1 to 1:2. This ratio range ensures that the surface of the silicon-carbon material is completely modified.

[0040] Additionally, step 01 includes: First, silicon-carbon material is dispersed in water to form a silicon-carbon material dispersion with a concentration of 1% to 10%. Then, a surface modifier is added to the silicon-carbon material dispersion, and the mixture is stirred thoroughly at a speed of 200 to 400 rpm for 3 to 5 hours. Finally, the modified silicon-carbon is obtained by centrifugation or filtration and drying. The above parameter settings enable more complete modification of the silicon-carbon material.

[0041] In addition, in step 02, the mass ratio of modified silicon carbon to water in the silicon carbon dispersion is 1:100~200, which improves the dispersion effect, and the solid fraction of the graphene oxide dispersion is 0.90%~0.92%.

[0042] In this embodiment, in step 03, the solid fraction of the graphene oxide dispersion is 0.1%~0.2%, which improves the dispersion effect of graphene oxide.

[0043] Furthermore, in step 03, the mass ratio of the primary coating material to graphene oxide is 100:1~7, which can ensure the integrity and thickness of the coating.

[0044] In addition, in step 03, the hydrothermal reaction conditions are: reacting at a temperature of 120℃~150℃ for 5~7 hours, thereby forming a cylindrical hydrogel in the reaction vessel.

[0045] In addition, in step 03, the drying temperature is 90℃~120℃ and the drying time is 8~12h.

[0046] In one specific 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.

[0047] 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.

[0048] In detail, the preparation process of silicon-carbon materials is as follows: First, the porous carbon material is placed in a tube furnace and replaced with an inert gas to ensure the oxygen content inside the furnace is less than 50 ppm, preventing the silicon source gas from exploding. Then, the furnace is heated to 400-600°C at a rate of 1°C / min to 10°C / min and held for 30 minutes to ensure that the temperature reaches the required value throughout the furnace. Finally, the silicon source gas is introduced into the tube furnace at an average flow rate of 1 L / min, and the reaction is allowed to proceed 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 the protection of the inert gas, the 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 heat preservation settings of the tube furnace and the control of the carbon source flow rate is to achieve uniform deposition of silicon microparticles. The purpose of the deposition temperature of 400~600℃ is to prevent the silicon particles from undergoing a carbonization reaction with the carbon source and carbon carrier while ensuring deposition, thus affecting the capacitance.

[0049] 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.

[0050] In addition, in step 02, the drying method is stirring drying. Specifically, the stirring speed is 100 rpm, and the stirring temperature is 90~120℃.

[0051] 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.

[0052] During the stirring and drying process, the sheet-like structure of graphene oxide 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).

[0053] 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 cycling performance.

[0054] Example 1 First, the silicon-carbon material was modified with polyethyleneimine, then filtered and dried to obtain a modified silicon-carbon filter cake. Next, the modified silicon-carbon filter cake was dispersed in deionized water to form a silicon-carbon dispersion. A 3522 graphene oxide dispersion was added dropwise to the silicon-carbon dispersion until the dispersion turned slightly yellow. After stirring for 30 minutes and allowing to settle, the mixture was filtered and dried to obtain a primary coating material. The primary coating material was then added to a 0.2% solid-phase graphene oxide dispersion and stirred at 150 rpm for 30 minutes. After stirring, the dispersion was poured into a hydrothermal reactor and hydrothermally treated at 180°C for 6 hours. After the hydrothermal reaction, the hydrogel formed was placed in an oven and dried at 80°C for 12 hours to obtain a secondary coating material. Finally, the secondary coating material was heated to 550°C at a heating rate of 1°C / min and then thermally reduced for 2 hours to obtain a secondary-coated graphene-coated silicon-carbon material (material sample).

[0055] A coin cell was constructed by assembling a half-cell of graphene-coated silicon-carbon material (material sample) with a binder-conductive agent ratio of 8:1:1; wherein the binder is PVDF (polyvinylidene fluoride) and the conductive agent is conductive carbon black; the coin cell was subjected to charge-discharge cycle testing at a current density of 0.3C, and the test results are shown in [reference needed]. Figure 2 and Figure 3The silicon-carbon sample coated by capillary force after two coating cycles retained about 90% of its capacity after 50 cycles, which is a high retention rate.

[0056] Comparative Example 1 First, the silicon-carbon material was modified with polyethyleneimine, then filtered and dried to obtain a modified silicon-carbon filter cake. Next, the modified silicon-carbon filter cake was dispersed in deionized water to form a silicon-carbon dispersion. A 3522 graphene oxide dispersion was then added dropwise to the silicon-carbon dispersion until the dispersion turned slightly yellow. After stirring for 30 minutes and allowing to settle, the mixture was filtered and dried to obtain a primary coated material. Finally, the primary coated material was heated to 550°C at a heating rate of 1°C / min and then subjected to thermal reduction for 2 hours to obtain a primary-coated graphene-coated silicon-carbon material (material sample).

[0057] A coin cell was constructed by assembling a half-cell of graphene-coated silicon-carbon material (material sample) with a binder-conductive agent ratio of 8:1:1; wherein the binder is PVDF (polyvinylidene fluoride) and the conductive agent is conductive carbon black; the coin cell was subjected to charge-discharge cycle testing at a current density of 0.3C, and the test results are shown in [reference needed]. Figure 2 and Figure 3 The silicon-carbon sample coated by precipitation alone retained approximately 67% of its capacity after 50 cycles, which is significantly lower than the retention rate obtained in Example 1.

[0058] Comparative Example 2 First, the silicon carbon material was modified with polyethyleneimine, then filtered and dried to obtain a modified silicon carbon filter cake. Next, the modified silicon carbon filter cake was added to a graphene oxide dispersion with a solid fraction of 0.2%, and stirred at 150 rpm for 30 minutes. After stirring, the dispersion was poured into a hydrothermal reactor and hydrothermally treated at 180℃ for 6 hours. The hydrogel formed by the hydrothermal reaction was then placed in an oven and dried at 80℃ for 12 hours. Finally, the hydrogel was heated to 550℃ at a heating rate of 1℃ / min and then thermally reduced for 2 hours to obtain the material sample.

[0059] A coin cell was assembled using a material sample: binder: conductive agent ratio of 8:1:1, where the binder was PVDF (polyvinylidene fluoride) and the conductive agent was conductive carbon black. The coin cell underwent charge-discharge cycle testing at a current density of 0.3C. The test results are shown in [link to test results]. Figure 2 and Figure 3 The capacity retention of silicon-carbon samples coated by capillary force after self-filling in a hydrothermal reactor was approximately 78% after 50 cycles.

[0060] Comparative Example 3 First, the silicon carbon material was modified with polyethyleneimine, then filtered and dried to obtain a modified silicon carbon filter cake. Next, the modified silicon carbon filter cake was added to a graphene oxide dispersion with a solid fraction of 0.2%, and stirred at 150 rpm for 30 minutes. After stirring, the dispersion was poured into a test tube and treated in a 90°C water bath for 12 hours. The hydrogel formed by the water bath heating was then placed in an oven and dried at 80°C for 12 hours. Finally, the hydrogel was heated to 550°C at a heating rate of 1°C / min and then held at that temperature for 2 hours for thermal reduction to obtain the material sample.

[0061] A coin cell was assembled using a material sample: binder: conductive agent ratio of 8:1:1, where the binder was PVDF (polyvinylidene fluoride) and the conductive agent was conductive carbon black. The coin cell underwent charge-discharge cycle testing at a current density of 0.3C. The test results are shown in [link to test results]. Figure 2 and Figure 3 After conventional heating treatment and self-packing, the silicon-carbon sample coated with capillary force retained approximately 61% of its capacity after 50 cycles.

[0062] Comparative Example 4 The silicon-carbon material was used directly as a material sample without any processing. A coin cell half-cell was assembled using the material sample, binder, and conductive agent in an 8:1:1 ratio; the binder was PVDF (polyvinylidene fluoride), and the conductive agent was conductive carbon black. A coin cell cycle test was conducted at a current density of 0.3C. The test results are shown in [link to relevant documentation]. Figure 2 and Figure 3 The capacity retention of untreated silicon-carbon silicon after 50 cycles is approximately 19%.

[0063] By comparing the above examples and comparative examples, it can be seen that compared to the uncoated silicon-carbon original sample, the capacity retention rate of the material sample formed by two coatings after 50 cycles is increased by about 50%, the capacity retention rate of the material sample formed by one coating after 50 cycles is increased by about 29%, and the capacity retention rate of the material sample formed by hydrothermal coating alone after 50 cycles is increased by about 40%. The results indicate that the integrity of a single modified coating may be relatively lower than that of a single hydrothermal capillary force coating, resulting in a relatively lower cycling performance. The material sample formed by two coatings shows improved integrity and mechanical strength of the surface coating layer, thus altering the cycling performance. Furthermore, by comparison... Figure 4 , Figure 5 , Figure 6 and Figure 7 It can be seen that the material sample formed by two coatings is significantly more complete than the material sample formed by a single coating. Figures 4-7 and Figure 8By comparing the uncoated silicon-carbon sample with the original sample, it can be seen that regardless of whether it is coated twice or once, graphene is clearly coated on the surface of silicon-carbon compared to the original sample.

[0064] 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.

[0065] 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, Surface modification: The silicon-carbon material is modified with a surface modifier to obtain modified silicon-carbon; Step 02, primary coating: The modified silicon carbon is dispersed in water to form a silicon carbon dispersion, and graphene oxide dispersion is added to the silicon carbon dispersion until the dispersion turns slightly yellow. Then, the mixture is filtered and dried to obtain the primary coating material. Step 03, Secondary Coating: The primary coating material is dispersed in a graphene oxide dispersion and a hydrogel is formed through a hydrothermal reaction. The hydrogel is then dried to obtain the secondary coating material. Step 04, thermal reduction treatment: The secondary coating material is heated and reduced to obtain graphene-coated silicon carbon material.

2. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 04, the heating method for the secondary coating material is stepped heating.

3. The method for preparing graphene-coated silicon-carbon material according to claim 2, characterized in that, The secondary coating material is first heated to 120°C at a heating rate of 1~10°C / min and held at that temperature for 1~6 hours; then heated to 150°C at a heating rate of 0.1~0.5°C / min and held at that temperature for 1~6 hours; then heated to 300°C at a heating rate of 0.1~0.5°C / min and held at that temperature for 1~6 hours; finally heated to 550°C at a heating rate of 1~5°C / min and held at that temperature for 1~2 hours before cooling to room temperature.

4. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 01, the mass ratio of silicon-carbon material to surface modifier is 1:1 to 1:

2.

5. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, The surface modifier is one or more of polyethyleneimine, polylysine, polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, hexadecyltrimethylammonium bromide, and polydopamine.

6. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, Step 01 includes: First, the silicon-carbon material is dispersed in water to form a silicon-carbon material dispersion with a concentration of 1% to 10%. Then, the surface modifier is added to the silicon-carbon material dispersion and stirred thoroughly at a speed of 200 to 400 rpm for 3 to 5 hours. Finally, the modified silicon-carbon is obtained by centrifugation or filtration and drying.

7. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 02, the mass ratio of modified silicon carbon to water in the silicon carbon dispersion is 1:100~200, and the solid fraction of the graphene oxide dispersion is 0.90%~0.92%.

8. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 03, the mass ratio of the primary coating material to graphene oxide is 100:1~7.

9. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 03, the solid fraction of the graphene oxide dispersion is 0.1% to 0.2%.

10. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 03, the hydrothermal reaction conditions are: reacting at a temperature of 120℃~150℃ for 5~7 hours.

11. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 03, the drying temperature is 90℃~120℃, and the drying time is 8~12h.

12. 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.

13. The method for preparing graphene-coated silicon-carbon material according to claim 12, 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. Then, the furnace is heated to 400-600°C at a heating rate of 1°C / min to 10°C / min and held for 30 min. Next, silicon source gas is introduced into the furnace at an average flow rate of 1 L / min, and the reaction is allowed to proceed for 40-80 min. Then, the silicon source gas is expelled from the furnace using an inert gas, and the furnace is heated to 500-550°C and held for 30 min. 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.

14. A graphene-coated silicon-carbon material, characterized in that, The graphene-coated silicon-carbon material is prepared using the method described in any one of claims 1-13.

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