Graphene coated silicon carbon material and preparation method thereof
By using stepped heating and cationic polymer modification, the problem of gas damage to the coating layer during the reduction of graphene oxide was solved, achieving high performance and stability of graphene-coated silicon-carbon materials and improving the electrochemical performance of the battery.
Patent Information
- Application Number
- CN202511707033.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-02-03
AI Technical Summary
When forming a graphene coating on a silicon-based anode, the large amount of gas generated during the reduction of graphene oxide leads to an incomplete coating, affecting the rate performance and cycle performance of the silicon-carbon anode.
A stepped heating method was used to reduce graphene oxide, and water-soluble cationic polymers were used to modify the silicon-carbon material. Electrostatic attraction was used to achieve the directional reduction of graphene oxide to graphene, preventing gas from damaging the integrity of the coating layer.
The prepared graphene-coated silicon-carbon material exhibits excellent rate performance and cycle performance, ensuring the structural stability and electrochemical performance of the material.
Smart Images
Figure CN121449044A_ABST
Abstract
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 the development of battery technology, the increasing miniaturization and high performance of electronic devices, along with the booming electric vehicle industry, have placed more stringent demands on battery performance. Silicon-based anode materials, with a theoretical specific capacity as high as 4200 mAh / g, can store more lithium ions of the same mass, and have a relatively low operating voltage (<0.5V). Furthermore, they are abundant in the Earth's crust, making them a highly promising anode material. However, silicon (Si) undergoes significant volume expansion (>300%) during the alloying / dealloying process during charging and discharging. This expansion leads to a series of problems, including material breakage, active material detachment, and instability of the solid electrolyte membrane, severely impacting battery stability and safety.
[0003] Graphene, as a novel carbon material, possesses advantages such as high specific surface area, excellent conductivity, and mechanical properties, making it widely applicable in the field of positive and negative electrode materials for charge conduction in lithium-ion batteries. Graphene coating can provide a volume buffer framework for silicon-based negative electrodes while also improving their conductivity. The effects of coating are as follows: 1) Alleviating volume effects: The coating layer can play a certain role in limiting and buffering, helping to maintain the stability of the electrode structure and preventing phenomena such as pulverization and shedding of electrode materials during charge and discharge, thereby improving the cycle performance of the battery. 2) Improving conductivity: Silicon itself is a semiconductor with poor conductivity, which severely limits its electrochemical performance at high rates. Graphene (a carbon material) has good conductivity; coating the surface of silicon-based negative electrodes can construct a continuous conductive network on the silicon surface, reducing the internal resistance of the battery and effectively improving the conductivity of the electrode, enabling rapid charge transfer and thus improving the charge and discharge performance of the battery. 3) Formation of a stable SEI film: The solid electrolyte interphase (SEI) layer formed by silicon-based anodes during charge and discharge is unstable and continuously consumes lithium ions, leading to lower initial efficiency and poor cycle stability. Graphene coating, however, makes the carbon-generated SEI film more stable and consumes less lithium ions, effectively preventing direct side reactions between the electrolyte and electrode materials, thereby improving the battery's cycle stability and safety. 4) Reduction of side reactions: Direct contact between silicon and electrolyte easily leads to unnecessary chemical reactions, causing electrolyte decomposition and reducing the battery's initial reversible capacity and coulombic efficiency. Graphene coating reduces direct contact between silicon and electrolyte, suppressing side reactions such as electrolyte decomposition and improving the battery's overall performance. 5) Improved electrode performance: Graphene coating can significantly improve the electrode performance of silicon-based anode materials, such as increasing specific capacity and reducing initial coulombic efficiency loss, enabling the battery to better meet the needs of different application scenarios.
[0004] Currently, when forming a graphene coating on a silicon-based anode, graphene oxide is first coated onto the silicon-based anode, and then the graphene oxide is reduced back to graphene. In this process, the reduction of graphene oxide is usually achieved by heating, i.e., directly heating the graphene oxide to 700-1200℃. Since graphene oxide is a single-atom-layer two-dimensional sheet material, it often exists in a multilayer state during actual preparation and application. When multiple layers of graphene oxide are attached to the silicon-based anode, the functional groups on the surface of the graphene oxide generate a large amount of gas due to the reduction. This large amount of gas breaks through the graphene oxide coating, causing the graphene oxide to detach from the surface of the silicon-based anode. This results in an incomplete graphene coating, significantly reducing its structural strength and leading to a deterioration in the rate performance and cycle performance of the silicon-carbon anode. 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: Disperse silicon carbon material in graphene oxide dispersion to form a mixture, stir for a preset time, and then dry to obtain graphene oxide coated silicon carbon. Step 02: Under the protection of an inert gas, 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 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; finally heated to 550°C at a heating rate of 1~5°C / min to obtain the graphene-coated silicon carbon material.
[0007] Furthermore, in step 01, before dispersing the silicon carbon material in the graphene oxide dispersion, the silicon carbon material is modified using a water-soluble cationic polymer.
[0008] Furthermore, the water-soluble cationic polymer is one or more of polydimethyldiallylammonium chloride, polydiallyldimethylammonium chloride, polymethacryloyloxyethyltrimethylammonium chloride, and silane coupling agents.
[0009] Furthermore, the mass ratio of the water-soluble cationic polymer to the silicon-carbon material is 1:0.3~0.5.
[0010] Furthermore, in step 01, the mass percentage of graphene oxide in the mixture is 0.1% to 5%.
[0011] Further, in step 01, the mass ratio of the silicon carbon material to the graphene oxide in the graphene oxide dispersion is 100:1~5.
[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 for a specified reaction time. 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] Furthermore, in step 01, the drying method is stirring drying.
[0015] Furthermore, the stirring speed during the stirring and drying process is 100~200 rpm, and the temperature during the stirring and drying process is 90~120℃.
[0016] 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.
[0017] The advantages and beneficial effects of this invention are: In the preparation method of this invention, a stepped heating method is used to reduce the graphene oxide layer coated on the silicon-carbon material, thereby achieving the directional reduction of graphene oxide to graphene. This effectively prevents the large amount of gas generated during the thermal reduction process from damaging the integrity of the graphene oxide coating layer and reduces thermal stress, allowing the reduced graphene layer to completely and tightly coat the silicon-carbon material. Furthermore, the graphene-coated silicon-carbon material prepared by this method has excellent rate performance and cycle performance. Attached Figure Description
[0018] 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 circuit capacity diagram is shown for the material samples prepared in Example 1, Comparative Example 1 and Comparative Example 4 when subjected to coin cell cycle testing at a current density of 0.3C. Figure 3 The graph shows the capacity retention of the material samples prepared in Example 1, Comparative Example 1, and Comparative Example 4 during coin cell cycle testing. Figure 4 Here are SEM images of the material samples from Example 1; Figure 5 The image shows the SEM characterization of the material sample in Comparative Example 4. Detailed Implementation
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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: Disperse silicon carbon material in graphene oxide dispersion to form a mixture, stir for a preset time, and then dry to obtain graphene oxide coated silicon carbon.
[0025] The graphene oxide dispersion is formed by dispersing graphene oxide filter cake (SE2430W-R) in water through methods such as stirring, shearing, homogenization, or shaking. The solid fraction of the graphene oxide dispersion is 0.1% to 4.5%. After dilution to 50 ppm, the absorbance (abs value) at 230 nm is not less than 0.95. If the absorbance (abs value) is lower than 0.95, it indicates poor dispersibility of graphene oxide in water, which will cause graphene oxide to clump together near silicon carbon particles during coating, easily leading to self-agglomeration or folding back into a page-like shape, failing to adhere to the silicon carbon material surface in a coated state. Furthermore, the preset stirring time is 1 to 24 hours.
[0026] Step 02: Under the protection of an inert gas, first heat the graphene oxide-coated silicon carbon to 120℃ at a heating rate of 1~10℃ / min and hold the temperature for 1~6h; then heat it to 150℃ at a heating rate of 0.1~0.5℃ / min and hold the temperature for 1~6h; then heat it to 300℃ at a heating rate of 0.1~0.5℃ / min and hold the temperature for 1~6h; finally heat it to 550℃ at a heating rate of 1~5℃ / min and hold the temperature for 1~2h before cooling it to room temperature to obtain graphene-coated silicon carbon material. Then, perform conventional pulverization (crusher, pulverizer, air jet mill) to obtain the finished powder material.
[0027] 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.
[0028] In summary, the preparation method of this invention employs a stepped heating method to reduce the graphene oxide layer coated on the silicon-carbon material, achieving the directional reduction of graphene oxide to graphene. This effectively prevents the large amount of gas generated during the thermal reduction process from damaging the integrity of the graphene oxide coating layer and reduces thermal stress, ensuring that the reduced graphene layer is completely and tightly coated on the silicon-carbon material. Furthermore, the graphene-coated silicon-carbon material prepared by this method exhibits excellent rate performance and cycling performance.
[0029] In step 01 of this embodiment, before dispersing the silicon carbon material in the graphene oxide dispersion, the silicon carbon material is modified with a water-soluble cationic polymer.
[0030] Specifically, a water-soluble cationic polymer with a decomposition temperature below 500℃ is dissolved in water to prepare a solution with a mass ratio of 0.01~30%. The silicon-carbon material is placed in the water-soluble cationic polymer solution and stirred for 1~24 hours. After stirring, the modified silicon-carbon material is obtained by filtration or centrifugation. The silicon-carbon material is a composite structure formed by silicon (Si) as the main active material and combined with carbon materials (such as graphite, carbon nanotubes, graphene, etc.).
[0031] Understandably, modifying the surface of silicon-carbon materials with a positive charge using water-soluble cationic polymers transforms the surface charge of the silicon-carbon material into a positive charge, while the surface of graphene oxide carries a negative charge. This cleverly utilizes electrostatic attraction to achieve the coating of silicon-carbon materials with graphene oxide, resulting in higher uniformity and stability of the coating. Furthermore, during the thermal reduction process, the graphene-coated silicon-carbon material maintains good structural stability, effectively preventing the separation of the graphene coating layer during charge and discharge, thus ensuring the reliability and stability of the material's performance.
[0032] In detail, the water-soluble cationic polymer is a polymer capable of positively modifying the surface of silicon carbon, including one or more of polydimethyldiallylammonium chloride, polydiallyldimethylammonium chloride, polymethacryloyloxyethyltrimethylammonium chloride, and silane coupling agents.
[0033] In this embodiment, in step 01, the mass percentage of graphene oxide in the mixture is 0.1% to 5%. This mass percentage of graphene oxide allows it to be better dispersed in the solution, thus enabling it to better adhere to silicon carbon.
[0034] Furthermore, in step 01, the mass ratio of silicon carbon material to graphene oxide in the graphene oxide dispersion is 100:1~5.
[0035] If the mass ratio of silicon carbon material to graphene oxide is less than the above-mentioned range, excess graphene oxide will form wrinkles on the silicon carbon material, thereby affecting the electrochemical performance of the graphene-coated silicon carbon material and reducing its initial efficiency.
[0036] First-cycle efficiency, also known as first-charge-discharge efficiency, is a key indicator for measuring the first-cycle performance of electrode materials or batteries, and directly reflects the reversibility and energy utilization efficiency of the materials.
[0037] 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.
[0038] 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.
[0039] In detail, the 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.
[0040] 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.
[0041] In addition, in step 01, the drying method is stirring drying. Specifically, the stirring speed is 100 rpm, and the stirring temperature is 90~120℃.
[0042] 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.
[0043] 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).
[0044] Furthermore, the mass ratio of water-soluble cationic polymer to silicon-carbon material is 1:0.3~0.5. This ratio ensures that the silicon-carbon surface can be completely modified, and after modification, the cationic polymer will block the pores of the porous carbon. During subsequent heat treatment, these blocked cationic polymers will carbonize into new amorphous carbon at high temperatures and remain in the pores of the porous carbon, thereby sealing the pores of the porous carbon. This prevents the electrolyte from directly contacting the silicon in the porous carbon pores and avoids the formation of a thicker SEI film.
[0045] 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.
[0046] Example 1 First, 10g of silicon carbon material was dispersed in 100ml of deionized water to form a silicon carbon material dispersion. A 1% (w / w) aqueous solution of polydimethyldiallylammonium chloride (PDMDAAC) was added to the silicon carbon material dispersion and stirred until homogeneous. Then, 10g of a 1% solid fraction graphene oxide dispersion was added to form a mixture, which was stirred for 1 hour. The mixture was then dried by stirring at 100 rpm and 100℃ to obtain graphene oxide-coated silicon carbon. Finally, under inert gas protection, the graphene oxide-coated silicon carbon was heated to 120℃ at a heating rate of 5℃ / min and held for 1 hour, then heated to 150℃ at a heating rate of 0.1℃ / min and held for 1 hour, then heated to 300℃ at a heating rate of 0.1℃ / min and held for 1 hour, and finally heated to 550℃ at a heating rate of 5℃ / min and held for 1 hour before cooling to room temperature to obtain the graphene-coated silicon carbon material (material sample).
[0047] After obtaining graphene-coated silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain finished powder material, which is then made into electrode material, and the rate performance and cycle performance of the electrode material are tested.
[0048] Comparative Example 1 First, 10g of silicon carbon material was dispersed in 100ml of deionized water to form a silicon carbon material dispersion. Then, a 1% (w / w) aqueous solution of polydimethyldiallylammonium chloride (PDMDAAC) was added to the silicon carbon material dispersion and stirred until homogeneous. Next, 50g of a 1% solid-phase graphene oxide dispersion was added to form a mixture. After stirring for 1 hour, the mixture was dried at 100 rpm and 100℃ to obtain graphene oxide-coated silicon carbon. Finally, under inert gas protection, the graphene oxide-coated silicon carbon was heated to 120℃ at a heating rate of 5℃ / min and held for 1 hour; then heated to 150℃ at a heating rate of 0.1℃ / min and held for 1 hour; then heated to 300℃ at a heating rate of 0.1℃ / min and held for 1 hour; finally, heated to 550℃ at a heating rate of 5℃ / min and held for 1 hour, and then cooled to room temperature to obtain the graphene-coated silicon carbon material (material sample). After obtaining graphene-coated silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain finished powder material, which is then made into electrode material, and the rate performance and cycle performance of the electrode material are tested.
[0049] Comparative Example 2 First, 10g of silicon carbon material was dispersed in 100ml of deionized water to form a silicon carbon material dispersion. A 1% (w / w) aqueous solution of polydimethyldiallylammonium chloride (PDMDAAC) was added to the silicon carbon material dispersion, and the mixture was stirred for 1 hour. Then, the mixture was stirred and dried at 100 rpm and 100°C to obtain silicon carbon coated with a modifier. Finally, under inert gas protection, the silicon carbon coated with the modifier was heated to 120°C at a heating rate of 5°C / min and held for 1 hour; then heated to 150°C at a heating rate of 0.1°C / min and held for 1 hour; then heated to 300°C at a heating rate of 0.1°C / min and held for 1 hour; finally, heated to 550°C at a heating rate of 5°C / min and held for 1 hour, and then cooled to room temperature to obtain the coated silicon carbon material (material sample).
[0050] After obtaining the coated silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain the finished powder material, which is then made into electrode material, and the rate performance and cycle performance of the electrode material are tested.
[0051] Comparative Example 3 First, 10g of silicon carbon material was dispersed in 100ml of deionized water to form a silicon carbon material dispersion. A 1% (w / w) aqueous solution of polydimethyldiallylammonium chloride (PDMDAAC) was added to the silicon carbon material dispersion and stirred until homogeneous. Then, 10g of a 1% solid fraction graphene oxide dispersion was added to form a mixture, which was stirred for 1 hour. The mixture was then dried by stirring at 100 rpm and 100°C to obtain graphene oxide-coated silicon carbon. Finally, under inert gas protection, the graphene oxide-coated silicon carbon was heated to 120°C at a heating rate of 5°C / min and held at that temperature for 3 hours. It was then heated to 300°C at a heating rate of 5°C / min and finally to 550°C at a heating rate of 5°C / min to obtain the graphene-coated silicon carbon material (material sample).
[0052] After obtaining graphene-coated silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain finished powder material, which is then made into electrode material, and the rate performance and cycle performance of the electrode material are tested.
[0053] Comparative Example 4 First, 10g of silicon carbon material was dispersed in 100ml of deionized water to form a silicon carbon material dispersion. Then, the silicon carbon material dispersion was stirred and dried at 100rpm and 100℃. Finally, under the protection of an inert gas, the graphene-coated silicon carbon was heated to 120℃ at a heating rate of 5℃ / min and held for 1h, then heated to 150℃ at a heating rate of 0.1℃ / min and held for 1h, then heated to 300℃ at a heating rate of 0.1℃ / min and held for 1h, then heated to 550℃ at a heating rate of 5℃ / min and held for 1h, and finally cooled to room temperature to obtain the silicon carbon material (material sample).
[0054] After obtaining the silicon-carbon material, it is subjected to conventional crushing (crusher, pulverizer, air jet mill) to obtain the finished powder material, which is then made into electrode material, and the rate performance and cycle performance of the electrode material are tested.
[0055] The material samples prepared in Example 1, Comparative Example 1, and Comparative Example 4 were subjected to coin cell cycle tests. The test results are shown in [Figure Number]. Figure 2 and Figure 3 ,pass Figure 2 and Figure 3It can be observed that when using the stirred-drying method to coat silicon carbon with graphene oxide, different amounts of graphene oxide added all have a positive effect on capacity retention and initial coulombic efficiency. However, the amount of graphene oxide added is important. Adding 1% relative to silicon carbon improves the initial efficiency by 5.3% and the capacity retention by 43.2% compared to the original sample, while the initial capacity remains almost unchanged. When the amount of graphene oxide added reaches 5%, the initial efficiency is improved by about 3.3% and the capacity retention by 50.6% compared to the original sample, but the initial capacity decreases by 8%, and the coating cost increases fivefold. Therefore, using 1% graphene oxide is more suitable for industrial production.
[0056] Figure 4 and Figure 5 The images show SEM images of the coated silicon-carbon sample and the original sample after the stirring-drying method, respectively. Figure 4 It can be observed that there is a large amount of clearly sheet-like graphene adhered to the surface of silicon carbon, proving that the coating integrity is high.
[0057] Table 1
[0058] The test results for each embodiment and comparative example are shown in Table 1.
[0059] By comparing Example 1 and Comparative Example 1, it can be seen that if the mass ratio of graphene oxide to silicon carbon material is too high, excess graphene oxide will form wrinkles on the silicon carbon material, which will reduce the initial efficiency and capacity retention of the prepared graphene-coated silicon carbon.
[0060] By comparing Example 1 and Comparative Example 2, it can be seen that simply using a polymer modifier to coat silicon-carbon materials does not significantly improve the initial efficiency and capacity retention of the resulting porous carbon. This indicates that graphene oxide is the key factor in improving electrochemical performance.
[0061] By comparing Example 1 and Comparative Example 3, it can be seen that when thermally reducing graphene oxide, if the heating rate is too fast, the large amount of gas produced will damage the integrity of the graphene oxide coating layer, resulting in poor integrity of the graphene coating layer and a significant reduction in the first efficiency and capacity retention of the prepared graphene-coated silicon carbon material.
[0062] By comparing Example 1 and Comparative Example 4, it can be seen that coating graphene onto silicon-carbon materials can significantly improve the material's first efficiency and capacity retention.
[0063] 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.
[0064] 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: Disperse silicon carbon material in graphene oxide dispersion to form a mixture, stir for a preset time, and then dry to obtain graphene oxide coated silicon carbon. Step 02: Under the protection of an inert gas, 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 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 to obtain the graphene-coated silicon carbon material.
2. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 01, before dispersing the silicon carbon material in the graphene oxide dispersion, the silicon carbon material is modified with a water-soluble cationic polymer.
3. The method for preparing graphene-coated silicon-carbon material according to claim 2, characterized in that, The water-soluble cationic polymer is one or more of polydimethyldiallylammonium chloride, polydiallyldimethylammonium chloride, polymethacryloyloxyethyltrimethylammonium chloride, and silane coupling agents.
4. The method for preparing graphene-coated silicon-carbon material according to claim 2, characterized in that, The mass ratio of the water-soluble cationic polymer to the silicon-carbon material is 1:0.3~0.
5.
5. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 01, the mass percentage of graphene oxide in the mixture is 0.1% to 5%.
6. The method for preparing graphene-coated silicon-carbon material according to claim 1, characterized in that, In step 01, the mass ratio of the silicon carbon material to the graphene oxide dispersion is 100:1~5.
7. 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.
8. The method for preparing graphene-coated silicon-carbon material according to claim 7, 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.
9. The method for preparing graphene-coated silicon-carbon material according to claim 7, characterized in that, In step 01, the drying method is stirring drying.
10. The method for preparing graphene-coated silicon-carbon material according to claim 9, characterized in that, The stirring speed during the stirring and drying process is 100~200 rpm, and the temperature during the stirring and drying process is 90~120℃.
11. 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 1-10.