Silicon-carbon composite material, preparation method and application thereof
By using a flexible inner carbon layer and a rigid outer carbon layer to surround nano-silicon particles in a silicon-carbon composite material, combined with g-C3N4 template and nitrogen doping, the problems of complex preparation and high cost of silicon-carbon anode materials are solved, and high-efficiency lithium battery performance is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 上虞半导体材料研究中心
- Filing Date
- 2026-03-26
- Publication Date
- 2026-06-05
Smart Images
Figure CN122158538A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemistry, specifically relating to a silicon-carbon composite material, its preparation method, and its application. Background Technology
[0002] With the development of technology, the performance of power batteries and consumer batteries, such as range, safety, and fast charging, urgently needs improvement. Silicon-based materials, due to their high specific capacity and high safety, have become ideal anode materials for future lithium-ion batteries. To overcome the high expansion of silicon particles, silicon-carbon composite materials have become an ideal solution.
[0003] Silicon-carbon materials, prepared by chemical vapor deposition (CVD) of nano-silicon particles into porous carbon pores and then coating them with a carbon layer, represent the most promising route for industrial-scale silicon-carbon anode material synthesis. However, the high cost of porous carbon, the core material of this method, makes silicon-carbon anodes significantly more expensive than traditional graphite anodes, hindering market adoption. Another approach involves a core-shell structure, with a silicon core inside and a carbon shell outside. However, the optimal configuration for this structure requires a gap between the carbon shell and the nano-silicon particles to prevent the silicon particles from expanding outwards and breaking the carbon shell during lithium intercalation. This yolk-shell structure often involves complex steps such as template filling and etching, using hazardous chemicals like hydrofluoric acid, making it unsuitable for mass production. Furthermore, the limited contact area between the silicon particles and the carbon shell in the yolk-shell structure restricts the conductivity of the silicon-carbon anode material. Therefore, the industry is pursuing a simple, safe, and readily available silicon-carbon material. Summary of the Invention
[0004] In view of the problems existing in the prior art, the purpose of this invention is to design and provide a technical solution for silicon-carbon composite materials, their preparation method and application.
[0005] The present invention is implemented using the following technical solutions: The first aspect of the present invention provides a silicon-carbon composite material, comprising a carbon layer skeleton and nano-silicon, wherein the carbon layer skeleton comprises a flexible inner carbon layer and a rigid outer carbon layer, the flexible inner carbon layer surrounds voids, the nano-silicon fills the space between the flexible inner carbon layer and the rigid outer carbon layer, and the nitrogen content of the carbon layer skeleton is 2 at% to 10 at%.
[0006] Furthermore, the specific surface area of the silicon-carbon composite material is less than 100 m². 2 / g; the particle size of the nano-silicon is less than 20nm, and the silicon content is 20wt% to 50wt%.
[0007] A second aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon composite material, comprising the following steps: S.1 Provide or prepare a g-C3N4 with a carbon-coated surface, i.e., use g-C3N4@C as a substrate for deposition; S.2 Take g-C3N4@C and place it in a vapor deposition furnace. Introduce protective gas and silicon source gas to form nano-silicon particles on the surface of g-C3N4@C to obtain Si / (g-C3N4@C) composite material. S.3 The Si / (g-C3N4@C) composite material was subjected to carbon coating treatment to obtain the Si / (g-C3N4@C)@C composite material; S.4 The Si / (g-C3N4@C)@C composite material is subjected to high-temperature treatment under a protective atmosphere to decompose g-C3N4, and the finished silicon-carbon composite material Si / C@C is obtained.
[0008] This invention utilizes the template effect of graphitic carbon nitride (g-C3N4) to first load nano-silicon particles onto g-C3N4 pre-coated with a carbon layer, then coat and protect the nano-silicon particles with a carbon layer, and finally decompose g-C3N4 at high temperature. This frees up the space originally occupied by g-C3N4 in the material, resulting in a silicon-carbon material with a carbon layer framework surrounding the voids and silicon particles contained between the inner and outer double carbon layers.
[0009] This invention uses pre-coated carbon layer g-C3N4 as a substrate. This carbon layer can be transformed into a flexible nitrogen-containing inner carbon layer at the decomposition temperature of g-C3N4. After silicon deposition, the coated carbon layer can become a rigid nitrogen-containing outer carbon layer at the decomposition temperature of g-C3N4. The nitrogen element is generated during the decomposition of g-C3N4. The inner carbon layer is flexible and can deform together with the silicon particles without breaking, thus buffering and confining the inward expansion of the silicon particles during lithium intercalation. Even if the deformation of the flexible carbon layer causes the voids it surrounds to collapse (i.e., it cannot support the voids), it can still leave voids around the silicon particles wrapped between the inner and outer carbon layers. The outer carbon layer is relatively thick and rigid, which can effectively inhibit the outward expansion of silicon particles, prevent the external electrolyte from failing to enter the internal pores, and reduce the specific surface area, thus reducing the consumption of active lithium during the formation of the silicon SEI film. The outer carbon layer is also doped with nitrogen, which can enhance the wettability of the electrolyte to the electrode, increase electronic conductivity, and increase the transport rate of lithium ions in the carbon material. Since the actual morphology of g-C3N4 is not necessarily regular, and silicon deposition and carbon coating depend on the morphology of g-C3N4, the shape of this silicon-carbon material is not regular. The ease of fabricating the template material g-C3N4 depends on the required morphology. The resulting silicon-carbon material avoids the step of using hazardous substances such as hydrofluoric acid to etch the template to obtain the porosity state. The novel silicon-carbon material prepared by this invention can guarantee the performance of lithium batteries, thus achieving a balance between cost reduction and performance, and has certain market application prospects.
[0010] Furthermore, the g-C3N4 in step S.1 is one of nanosheets and their assemblies, nanorods and their assemblies, or nanospheres and their assemblies. The g-C3N4 is coated with a carbon layer, which is prepared by liquid phase coating plus carbonization or vapor phase deposition.
[0011] Different morphologies and sizes of g-C3N4 nanomaterials can be prepared using different raw materials and methods to meet varying requirements for silicon-carbon composite parameters. The coating effect of the pre-coated carbon layer on g-C3N4 also differs depending on the method used.
[0012] Furthermore, in step S.2, the protective gas in the vapor deposition furnace includes one of nitrogen and argon, and the vapor deposition furnace is one of a tube furnace and a rotary kiln; the silicon source gas includes one of silane, disilane, trisilane, and tetrasilane.
[0013] Furthermore, the carbon coating method in step S.3 is one of one-step vapor phase deposition and one of vapor phase deposition followed by liquid phase coating and carbonization; the carbon source gas in the vapor phase deposition method includes one of methane, ethane, propylene and acetylene, and the vapor phase deposition furnace is one of a tube furnace and a rotary kiln.
[0014] Furthermore, the polymer used for liquid phase coating includes one of phenolic resin, polydopamine, and polyvinyl alcohol, or is prepared in situ using the corresponding polymer precursor.
[0015] The structure and composition of the outer carbon coating will also change during the next step of g-C3N4 decomposition. When using vapor-phase coating in this step, the gas parameters must be adjusted to ensure the carbon layer coats every location containing silicon nanoparticles. Before liquid-phase coating, the first step of vapor-phase deposition coating must be performed because this first step covers the silicon particles with a carbon layer, preventing oxidation of the silicon particles after the material is removed from the vapor deposition furnace. The carbonization of the coating described in this invention can be completed simultaneously with the g-C3N4 decomposition in step S.4.
[0016] Furthermore, in step S.4, the heat treatment temperature is 700~800℃, and the treatment time is 2~4 hours; the protective gas includes either nitrogen or argon, and the high-temperature treatment furnace is either a tube furnace or a rotary kiln.
[0017] This heat treatment step not only allows the internal g-C3N4 to decompose and leave voids, but also transforms the inner carbon layer (the carbon layer pre-coated on g-C3N4) into a flexible nitrogen-containing carbon layer, and increases the orderliness of the outer carbon layer (the carbon layer covering silicon particles and the inner carbon layer). The embedding of nitrogen atoms can improve the electronic conductivity and lithium-ion transport speed of the material.
[0018] The third aspect of this invention provides the application of silicon-carbon composite materials and their preparation methods in the preparation of silicon-carbon anode materials.
[0019] The present invention has the following beneficial effects: (1) The silicon-carbon material with a double carbon layer framework surrounding the voids used in this application can obtain a more ideal first coulombic efficiency and electrode expansion rate. The double carbon layer framework of silicon-carbon can induce the nano-silicon particles to expand into the internal voids, providing a buffer and confinement effect for their lithium intercalation expansion.
[0020] (2) The nitrogen element contained in the carbon layer of this application can increase electronic conductivity and the transport speed of lithium ions in the carbon layer.
[0021] (3) The preparation method of the silicon-carbon composite material of this application is simple and convenient, and the conditions are clear and simple, which is conducive to further production and application in subsequent production activities. Attached Figure Description
[0022] Figure 1 A brief example of a method for preparing silicon-carbon composites. Detailed Implementation
[0023] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. Unless otherwise specified, the methods used in the embodiments of the present invention are conventional methods, and the reagents used are commercially available.
[0024] Preparation methods of silicon-carbon composites, such as Figure 1 As shown.
[0025] Example 1: (1) Preparation of g-C3N4@C: The precursor g-C3N4 coated with glucose-derived carbon (g-C3N4@Glucose) can be prepared according to the literature. The specific steps are as follows: 15 g of urea is placed in a 100 mL crucible with a lid, heated to 550 °C at a heating rate of 5 °C / min, and held for 4 hours. The resulting yellow powder is ground to obtain uniform g-C3N4 powder. Sufficient g-C3N4 can be obtained by multiple batches. 5 g of g-C3N4 is ultrasonically dispersed in 400 mL of 0.3 M glucose solution for 4 hours. The resulting suspension is transferred to a 500 mL hydrothermal reactor and hydrothermally treated at 150 °C for 10 hours. After centrifugation, washing and drying, glucose-derived carbon coated g-C3N4, i.e., g-C3N4@Glucose, is obtained. g-C3N4@Glucose was carbonized in a tube furnace at 550°C under a nitrogen atmosphere for 2 hours to obtain g-C3N4@C. After carbonization at this temperature, the coated carbon layer and the coated g-C3N4 remained stable at subsequent silicon deposition and carbon coating temperatures not exceeding 550°C.
[0026] (2) 5.5 g of g-C3N4@C was placed in a rotary tube furnace, and after purging with nitrogen, the temperature was raised to 480°C. The Si / (g-C3N4@C) composite was deposited for 45 minutes under the conditions of 5% silane volume concentration and 0.08 m / min apparent gas velocity.
[0027] (3) After heating to 550°C in a nitrogen atmosphere in a rotary tube furnace, a carbon-based amorphous coating was formed on the surface of the composite by deposition for 24 minutes under an acetylene volume concentration of 10%, resulting in Si / (g-C3N4@C)@C.
[0028] (4) The atmosphere of the rotary tube furnace is changed to nitrogen and heated to 800°C at 1°C / min and treated for 3 hours to decompose g-C3N4. At the same time, the inner and outer carbon layers are further carbonized and nitrogen elements are embedded to obtain Si / C@C.
[0029] This invention attempts to utilize the template effect of graphitic carbon nitride (g-C3N4) to first load nano-silicon particles onto a pre-coated carbon layer g-C3N4 substrate, then coat and protect the nano-silicon particles with a carbon layer, and finally decompose g-C3N4 at high temperature. This frees up the space originally occupied by g-C3N4 in the material, resulting in a silicon-carbon material with a carbon layer framework surrounding the voids and silicon particles contained between the inner and outer double carbon layers.
[0030] Besides serving as a sacrificial template, g-C3N4 can also provide nitrogen atoms to the inner and outer carbon layers and alter their structure during decomposition. The inner carbon layer is flexible and can deform along with the silicon particles without breaking, buffering and confining the inward expansion of silicon during lithium intercalation. If the deformation of the flexible carbon layer causes the collapse of the voids it surrounds, it can actually create voids around the silicon particles encased between the inner and outer carbon layers. The outer carbon layer is relatively rigid, effectively suppressing the outward expansion of silicon particles, preventing external electrolyte from entering the internal pores, and reducing the specific surface area, thus reducing the consumption of active lithium during the formation of the silicon SEI film. The outer carbon layer is also doped with nitrogen, which can enhance the wettability of the electrolyte to the electrode, increase electronic conductivity, and increase the transport rate of lithium ions in the carbon material. In this example, the template g-C3N4 meets the morphological requirements and is simple to prepare. The silicon-carbon material obtained by this invention avoids the need to use hazardous substances such as hydrofluoric acid to etch templates to obtain voids. The novel silicon-carbon material prepared by this invention can guarantee the performance of lithium batteries, thus achieving a balance between cost reduction and performance, and has certain market application prospects. The silicon-carbon composite of Example 1 was characterized, and its specific surface area, as measured by a specific surface adsorption analyzer, was 25.3 m². 2 / g; TEM electron microscopy revealed that the silicon nanoparticles in the silicon-carbon composite had a particle size of approximately 15nm; the silicon content of the silicon-carbon composite was determined to be 42.6wt% by the loss on ignition method.
[0031] Example 2: The difference between this example and Example 1 is that the carbon coating is performed in two stages: first, gas phase coating is used, followed by liquid phase coating and carbonization. The Si / (g-C3N4@C) composite obtained in step (2) of Example 1 was deposited in a rotary tube furnace at 550°C and 10% acetylene volume concentration for 20 minutes to form a carbon-based amorphous coating on the surface of the composite. After cooling, Si / (g-C3N4@C)@C was obtained. Si / (g-C3N4@C)@C was added to an ethanol solution of phenolic resin (PF), stirred for 24 hours, and then the ethanol was evaporated at 70°C. The mixture was then dried in a vacuum oven for 12 hours to obtain Si / (g-C3N4@C)@C@PF powder. Finally, Si / (g-C3N4@C)@C@PF was transferred into a tube furnace and slowly heated to 800℃ for 3 hours under a nitrogen atmosphere. At the same time, g-C3N4 was decomposed and PF was carbonized, and the inner and outer carbon layers were further carbonized to obtain Si / C@C.
[0032] Comparative Example 1: The difference between this example and Example 1 is that pure g-C3N4 is used as the substrate. The specific steps are as follows: A uniform g-C3N4 powder is obtained as in Example 1. 5 grams of g-C3N4 are placed in a rotary tube furnace, and the temperature is raised to 480°C under nitrogen purging. Deposition is carried out for 45 minutes under conditions of 5% silane volume concentration and an apparent gas velocity of 0.08 m / min to form Si / gC. The 3N4 composite was then heated to 550°C and deposited for 30 minutes at a 10% acetylene volume concentration to form a carbon-based amorphous coating on the composite surface, yielding Si / g-C3N4@C. Finally, the atmosphere was switched to nitrogen and the temperature was increased to 800°C at 1°C / min for 3 hours to decompose g-C3N4, yielding Si@C.
[0033] Comparative Example 2: The difference between this example and Example 1 is that g-C3N4 is not decomposed. That is, the Si / g-C3N4@C obtained in Example 1 is cooled down and directly taken out of the rotary tube furnace for use without further heating and decomposition.
[0034] Electrode and half-cell preparation and electrochemical performance testing (as shown in Table 1): Using the silicon-carbon anode materials prepared in the above embodiments and comparative examples as the anode active materials, anode sheets were prepared respectively. The anode sheets were used to prepare CR2016 coin cells using conventional methods, and the electrical performance of the cells was tested. The specific testing methods are as follows: (1) Preparation of negative electrode sheet: The prepared negative electrode material, conductive material (Super P:CMC = 3:1, mass ratio) and binder (polyacrylate) are mixed using a Thinky mixer at a mass ratio of negative electrode material: conductive material: binder = 80: 10: 10 to obtain a slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil and dried at 85°C and cold-pressed to obtain the negative electrode sheet.
[0035] (2) Half-cell assembly: Assemble CR2016 coin cells in a glove box, using a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1:1), containing 5% fluoroethylene carbonate (FEC) and 0.5% vinylene carbonate (VC). Assemble the above negative electrode, separator, and counter electrode, and inject the electrolyte to obtain the coin cell.
[0036] (3) Cyclic specific capacity and initial efficiency test: After the CR2016 button cell was left to stand for 2 hours, it was discharged to 0.005V at 0.05C; then discharged to 0.005V at 50μA; after standing for 10 minutes, it was charged to 1.5V at 0.1C constant current; the initial delithiation specific capacity is the specific capacity (or mass specific capacity) of the electrode material, and the ratio of the initial delithiation capacity to the initial lithium insertion capacity is the initial coulombic efficiency of the battery.
[0037] (4) Electrode expansion rate: After the CR2016 type button cell was left to stand for 12 hours, it was discharged at 0.1C to 0.01V; then discharged at 0.08C to 0.005V; and finally discharged at 0.05C to 0.005V; then the button cell was disassembled in the glove box, the electrode was cleaned with DMC and the electrode thickness was measured; Electrode expansion rate = (Electrode thickness in the first fully charged state - fresh electrode thickness) / fresh electrode thickness × 100%. Note: The thickness of the copper foil substrate should be deducted from the electrode thickness.
[0038] Table 1 Capacity (mAh / g) First Coulomb efficiency % Electrode expansion rate % Example 1 1537 86.9% 72.4% Example 2 1524 86.1% 84.5% Comparative Example 1 1459 82.2% 82.1% Comparative Example 2 812 80.1% 133.2% .
[0039] Examples 1 and 2, using Si / C@C, a silicon-carbon material containing voids, achieved an initial coulombic efficiency of over 80% and an electrode expansion rate of less than 90%. This indicates that after the decomposition of g-C3N4, voids are formed within the inner carbon layer. The inner flexible carbon layer can deform together with the nano-silicon particles without breaking, providing a buffer for their inward expansion during lithium intercalation. If the deformation of the flexible carbon layer causes the voids it surrounds to collapse, it can actually leave voids around the silicon particles encased between the inner and outer carbon layers. In Comparative Example 2, g-C3N4 was not removed, resulting in significant compression of the nano-silicon particles by the inner carbon layer. The expansion of the silicon particles creates pressure on the outer carbon layer, leading to a relatively higher electrode expansion rate. Because g-C3N4 was not decomposed and removed in Comparative Example 2, the overall silicon content was lowered, resulting in a significantly lower specific capacity compared to the other examples. Example 2 used Si / C@C prepared by sequentially coating with vapor phase and liquid phase deposition methods. In a single charge-discharge test of a half-cell, its performance level was comparable to that of Example 1.
[0040] Comparative Example 1 uses pure g-C3N4 as a substrate, then deposits silicon and coats it with carbon. After decomposing g-C3N4, the nano-silicon in the resulting silicon-carbon material Si@C is only wrapped by an outer carbon layer, but not by an inner carbon layer. The particles are prone to falling into the cavity during charging and discharging, which has a negative impact on specific capacity and first-time efficiency.
[0041] This specification is not limited to the embodiments described above, but various modifications can be made without departing from the technical concept of this specification. Other ways of constructing the embodiments by combining some of the constituent elements are also included within the scope of this application. The scope of protection of this specification should be interpreted according to the scope of the invention claims.
Claims
1. A silicon-carbon composite material, characterized in that, It includes a carbon layer framework and nano-silicon. The carbon layer framework includes a flexible inner carbon layer and a rigid outer carbon layer. The flexible inner carbon layer surrounds voids, and the nano-silicon fills the space between the flexible inner carbon layer and the rigid outer carbon layer. The nitrogen content of the carbon layer framework is 2 at% to 10 at%.
2. The silicon-carbon composite material as described in claim 1, characterized in that, The specific surface area of the silicon-carbon composite material is less than 100 m². 2 / g; the particle size of the nano-silicon is less than 20nm, and the silicon content is 20wt% to 50wt%.
3. A method for preparing the silicon-carbon composite material as described in claim 1 or 2, characterized in that, Includes the following steps: S.1 Provide or prepare a g-C3N4 with a carbon-coated surface, i.e., use g-C3N4@C as a substrate for deposition; S.2 Take g-C3N4@C and place it in a vapor deposition furnace. Introduce protective gas and silicon source gas to form nano-silicon particles on the surface of g-C3N4@C to obtain Si / (g-C3N4@C) composite material. S.3 The Si / (g-C3N4@C) composite material was subjected to carbon coating treatment to obtain the Si / (g-C3N4@C)@C composite material; S.4 The Si / (g-C3N4@C)@C composite material is subjected to high-temperature treatment under a protective atmosphere to decompose g-C3N4, and the finished silicon-carbon composite material Si / C@C is obtained.
4. The method for preparing a silicon-carbon composite material as described in claim 3, characterized in that, In step S.1, g-C3N4 is one of nanosheets and their assemblies, nanorods and their assemblies, or nanospheres and their assemblies. The g-C3N4 is coated with a carbon layer, which is prepared by liquid phase coating plus carbonization or vapor phase deposition.
5. The method for preparing a silicon-carbon composite material as described in claim 3, characterized in that, In step S.2, the protective gas in the vapor deposition furnace includes one of nitrogen and argon, and the vapor deposition furnace is one of a tube furnace and a rotary kiln; the silicon source gas includes one of silane, disilane, trisilane, and tetrasilane.
6. The method for preparing a silicon-carbon composite material as described in claim 3, characterized in that, In step S.3, the carbon coating method is one of one-step vapor phase deposition and one of vapor phase deposition followed by liquid phase coating and carbonization; the carbon source gas for the vapor phase deposition method includes one of methane, ethane, propylene and acetylene, and the vapor phase deposition furnace is one of a tube furnace and a rotary kiln.
7. The method for preparing a silicon-carbon composite material as described in claim 6, characterized in that, The polymer used for liquid phase coating includes one of phenolic resin, polydopamine, and polyvinyl alcohol, or is prepared in situ using the corresponding polymer precursor.
8. The method for preparing a silicon-carbon composite material as described in claim 3, characterized in that, The heat treatment temperature in step S.4 is 700~800℃, and the treatment time is 2~4 hours; the protective gas includes either nitrogen or argon, and the high-temperature treatment furnace is either a tube furnace or a rotary kiln.
9. The application of the silicon-carbon composite material as described in any one of claims 1-2 or the preparation method as described in any one of claims 3-8 in the preparation of silicon-carbon anode materials.