A Composite Carbon Layer-Coated Graphite-Matched Silicon Carbide Material and Its Preparation Method

Abstract

The present invention provides a composite carbon layer-coated graphite-matched silicon-carbon material and a preparation method thereof. The steps of the preparation method include: coating asphalt on a graphite substrate to obtain coated graphite; introducing a carbon source gas to perform chemical vapor deposition on the coated graphite to generate a graphite nano-bridging structure with a specific orientation on the surface of the coated graphite to obtain modified graphite; preparing a silicon-carbon substrate and mixing it with the modified graphite to obtain a composite carbon layer-coated graphite-matched silicon-carbon material. By constructing a graphite nano-bridging structure and a carbon layer, the synchronous transmission efficiency of electrons and lithium ions is improved, the resistance is reduced, and the charge and discharge efficiency of the battery is improved. By introducing a silicon-carbon substrate, the lithium storage capacity of the material is significantly improved, and the charge and discharge capacity of the battery is increased. The graphite nano-bridging structure and the porous carbon layer structure enhance the structural stability of the material, reduce the pulverization and capacity attenuation of the material caused by the volume expansion of silicon, and improve the service life of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a composite carbon layer-coated graphite-matched silicon-carbon material and a preparation method thereof. Background Art

[0002] With the rapid development of modern technology, lithium-ion batteries, as an efficient and portable energy storage device, have extensive and crucial applications in many fields such as electric vehicles and portable electronic devices. Currently, graphite is one of the most commonly used anode materials for lithium-ion batteries. It has many advantages, such as good electrical conductivity, stable chemical properties, and a relatively mature preparation process, which makes it play an important role in the commercialization process of lithium-ion batteries. However, the graphite anode also has a significant shortcoming, that is, its energy density is relatively low. In the current situation of pursuing higher energy density to meet the needs of fields such as long-range electric vehicles, this limitation becomes more and more prominent. Simply relying on graphite as the anode material is difficult to achieve a breakthrough improvement in the performance of lithium-ion batteries.

[0003] In order to overcome the problem of low energy density of the graphite anode, the introduction of silicon-based anodes has become a research hotspot. In theory, silicon-based materials have extremely high specific capacities and have the potential to significantly improve the energy density of batteries compared with graphite. Given the problem of insufficient energy density of the graphite anode, the introduction of silicon-based anode materials has become the focus direction of current research. Silicon-based anodes have extremely high specific capacities and have the potential to significantly improve the energy density of batteries compared with graphite.

[0004] However, if the silicon-based anode is directly and simply mixed with graphite, a series of intractable problems will arise:

[0005] (1) From the perspective of the material's own characteristics, the volume expansion phenomenon of silicon during charge and discharge is extremely significant. Compared with graphite, the silicon atomic radius is relatively large. When lithium ions are inserted and extracted, the silicon lattice will undergo severe deformation, and its volume expansion rate can be as high as 300% - 400%. When directly mixed with graphite, this large-scale volume change will cause serious damage to the overall structure of the electrode. On the one hand, it will cause cracks to appear inside the electrode material and an increase in pores, resulting in a worse contact between the active material and the current collector, blocking the electron conduction path, and increasing the internal resistance of the battery; on the other hand, the instability of the electrode structure will also cause the shedding of the active material, reducing the charge and discharge capacity of the battery.

[0006] (2)In terms of the differences in electrochemical performance, there are also essential differences between graphite and silicon. Graphite has a relatively stable charge-discharge potential plateau. The process of lithium-ion insertion and extraction between graphite layers is relatively gentle and follows a relatively stable diffusion mechanism. However, the charge-discharge potential range of silicon is different from that of graphite, and its electrochemical reaction kinetics process is more complex. The rate of lithium-ion insertion and extraction is inconsistent with that of graphite. After simple mixing of the two, during the charge-discharge cycle, the potential distribution in different regions of the electrode is uneven, resulting in an exacerbation of the polarization phenomenon. The generation of polarization requires a higher voltage during charging and a lower voltage during discharging for the battery, causing ineffective energy loss and directly reducing the charge-discharge efficiency of the battery.

[0007] (3)From the perspective of the lithium-ion transport process, due to the vastly different microstructures of graphite and silicon, the diffusion coefficients of lithium ions in the two are quite different. Graphite has a regular layered structure, which is conducive to the rapid diffusion of lithium ions between layers; the crystal structure of silicon is relatively complex, and the diffusion resistance of lithium ions in it is large. After mixing, during charge and discharge, lithium ions will preferentially choose the graphite region with less diffusion resistance for insertion and extraction, resulting in a locally excessive lithium-ion concentration, forming a concentration gradient and triggering lithium-ion crosstalk. Lithium-ion crosstalk not only disrupts the normal charge-discharge sequence and deforms the charge-discharge curve of the battery, but also accelerates the attenuation of the battery capacity. Because the aggregation of lithium ions in unexpected regions may react with the electrolyte to generate some lithium salt deposits that are difficult to decompose. These deposits adhere to the electrode surface, further hindering lithium-ion transport, forming a vicious cycle, and ultimately leading to a significant shortening of the battery life. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a composite carbon layer-coated graphite-matched silicon-carbon material and its preparation method, aiming to solve the problems of reduced charge-discharge capacity and charge-discharge efficiency of the battery and shortened battery life.

[0009] To solve the above technical problems, the present invention is implemented as follows. The present invention provides a preparation method for a composite carbon layer-coated graphite-matched silicon-carbon material, and the steps include:

[0010] S1. Coating asphalt on a graphite substrate to obtain coated graphite;

[0011] S2. Introducing a carbon source gas for chemical vapor deposition on the coated graphite to generate a graphite nano-bridging structure with a specific orientation on the surface of the coated graphite, obtaining modified graphite;

[0012] S3. Preparing a silicon-carbon substrate and mixing it with the modified graphite to obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0013] In some embodiments of the present invention, in step S1, the graphite substrate includes at least one of natural graphite, primary particle graphite, secondary particle graphite, needle coke graphite, petroleum coke graphite, green coke graphite, and calcined coke graphite, the pitch includes β-resin, and the content of the β-resin in the pitch is 10-80%.

[0014] In some embodiments of the present invention, step S1 includes:

[0015] S1.1. Ultrasonically disperse the pitch in absolute ethanol for 15-60 min to form a pitch emulsion;

[0016] S1.2. Transfer the pitch emulsion to a constant temperature water bath. Under the condition that the temperature is controlled at 40-90 °C, add the graphite substrate to the pitch emulsion, control the stirring speed at 300-500 rpm, and continuously stir for 1-3 hours until the absolute ethanol completely volatilizes;

[0017] S1.3. After the stirring is completed, transfer it to a vacuum oven and continuously vacuum dry it at 60-80 °C for 12-24 hours to obtain coated graphite.

[0018] In some embodiments of the present invention, step S1 includes:

[0019] S1.1. Preheat the pitch to 80-120 °C and keep stirring for 30-90 minutes. At the same time, add graphene or carbon nanotubes to obtain a rheological pitch;

[0020] S1.2. Perform solid-phase mixing of the rheological pitch and the graphite substrate in a VC mixer. Set the revolution speed of the VC mixer to 30-150 r / min, the rotation speed to 50-200 r / min, and the mixing time to 0.5-5 hours. During the mixing process, intermittently use ultrasonic-assisted dispersion with a frequency of 20-40 kHz, and the ultrasonic treatment time for each time is 10-20 minutes. After the mixing is completed, coated graphite is obtained.

[0021] In some embodiments of the present invention, calculated by weight percentage, in the coated graphite, the pitch accounts for 10-40 wt%, and the graphite substrate accounts for 60-90%.

[0022] In some embodiments of the present invention, step S2 includes:

[0023] S2.1. Uniformly lay the coated graphite in a quartz boat, then place the quartz boat in the constant temperature zone of a tube furnace, evacuate the tube furnace, and introduce an inert gas;

[0024] S2.2. Increase the temperature to 500 - 1400 °C at a heating rate of 0.5 - 5 °C / min, maintain the temperature and continuously introduce a carbon source gas for chemical vapor deposition, adjust the environmental pressure to 10 - 50 Pa, and control the deposition time within 30 - 120 minutes to generate a graphite nano - bridging structure with the same orientation as the gas flow direction;

[0025] S2.3. After the deposition is completed, stop introducing the carbon source gas and only introduce an inert gas, keep the temperature for 1 - 20 hours, then slowly cool down to 100 - 800 °C at a cooling rate of 0.5 - 5 °C / min, and then cool down to room temperature naturally to obtain modified graphite.

[0026] In some embodiments of the present invention, in step S2, the inert gas includes at least one of nitrogen, argon, and hydrogen, the flow rate of the inert gas is 1 - 20 L / min, and the carbon source gas includes at least one of ethylene and hydrogen with a volume ratio of 2:1, methane and hydrogen with a volume ratio of 4:1, and acetylene and hydrogen with a volume ratio of 1:1.

[0027] In some embodiments of the present invention, step S3 includes:

[0028] S3.1. Mix the porous carbon precursor and the silicon source material, and under the protection of an inert gas, heat it to 400 - 700 °C at a rate of 2 - 5 °C / min and keep the temperature for 2 - 4 hours to obtain a silicon - carbon base material;

[0029] S3.2. Mix the silicon - carbon base material and the modified graphite in a VC mixer according to a specific mass ratio, set the revolution speed of the VC mixer at 20 - 120 r / min and the rotation speed at 40 - 180 r / min, and mix for 0.5 - 4 hours to obtain a composite carbon - layer - coated graphite - matched silicon - carbon material.

[0030] In some embodiments of the present invention, in step S3, the porous carbon precursor includes at least one of biomass carbon, pitch carbon, and resin carbon, the silicon source material includes at least one of sodium silicate, tetraethoxysilane, and nano - silicon powder. Calculated by mass ratio, the porous carbon precursor: the silicon source = (2 - 5):1. The silicon - carbon base material includes internal pores and nano - silicon particles located in the internal pores. The size of the nano - silicon particles is 0.1 - 50 nm, and the size of the internal pores is 0.1 - 100 nm.

[0031] The present invention provides a composite carbon - layer - coated graphite - matched silicon - carbon material, which is prepared by the preparation method of the composite carbon - layer - coated graphite - matched silicon - carbon material as described above. The composite carbon - layer - coated graphite - matched silicon - carbon material includes pitch, a graphite substrate, a graphite nano - bridging structure, and a silicon - carbon base material; wherein,

[0032] The asphalt is used to form a carbon-coated layer, optimizing the interfacial bonding between the carbon-coated layer and the graphite substrate;

[0033] The graphite substrate is used to provide a stable conductive framework and structural support;

[0034] The graphite nanobridging structure is used to strengthen the conductive network, enhancing the overall structural stability and conductive performance of the material, and effectively buffering the stress of lithium ions during charge and discharge;

[0035] The silicon-carbon substrate is used to increase the overall theoretical specific capacity of the material, while buffering the volume expansion of silicon during charge and discharge.

[0036] Compared with the prior art, a composite carbon layer-coated graphite-matched silicon-carbon material and its preparation method in the present invention have the beneficial effects as follows:

[0037] In step S1, by coating the asphalt on the surface of the graphite substrate, the asphalt is carbonized under high-temperature conditions to generate a carbon layer with good conductivity. The carbon layer can enhance the electrical contact between the graphite substrates, improve the overall electron migration rate, effectively optimize the interface between the graphite and the electrolyte, and improve the integrity of the conductive network, thereby enhancing the charge and discharge efficiency and battery life. The carbon layer can block the direct reaction between the electrolyte and the graphite, reduce side reactions, and the stable interface reduces irreversible lithium loss, maintaining the effective utilization rate of active lithium ions. In step S2, the graphite nanobridging structure generated by chemical vapor deposition can optimize the electron and ion transport paths of the material at the micro level, while alleviating the volume expansion effect of the battery: the graphite nanobridging structure builds a three-dimensional electron migration path at the micro scale, shortening the electron diffusion distance. Even under high-rate charge and discharge conditions, it can maintain a low resistance, ensuring fast electron transport. The graphite nanobridging structure provides mechanical support for the silicon-carbon substrate, preventing the silicon from pulverizing due to volume expansion during charge and discharge. The structural integrity maintains the conductive path of the electrode, extending the cycle life. The ordered orientation of the graphite nanobridging structure can optimize the lithium ion insertion and extraction paths, reducing the risk of lithium dendrite formation, preventing short circuits and capacity decay, and improving the charge and discharge capacity and stability. In step S3, the silicon-carbon substrate is mixed with the modified graphite to form a composite material with a porous structure, taking into account both high capacity and structural stability. Through the combination of silicon and graphite, the high-capacity characteristics of silicon can be fully released. The carbon layer and the graphite nanobridging structure act together to absorb the stress generated by volume expansion. The graphite nanobridging structure provides an electron transport path, and the pores of the silicon-carbon substrate provide a diffusion path for lithium ions. The synchronism of electron and ion transport improves the overall charge and discharge efficiency. Description of the Drawings

[0038] Figure 1 is a TEM image of the composite carbon layer-coated graphite-matched silicon-carbon material in an embodiment of the present invention;

[0039] Figure 2 XRD patterns of the examples and comparative examples of the composite carbon layer-coated graphite matching silicon-carbon materials in an embodiment of the present invention;

[0040] Figure 3 Raman spectra of the examples and comparative examples of the composite carbon layer-coated graphite matching silicon-carbon materials in an embodiment of the present invention. Detailed implementation manners

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] The present invention provides a preparation method for a composite carbon layer-coated graphite matching silicon-carbon material, and the steps include:

[0043] S1. Coating asphalt on a graphite substrate to obtain coated graphite. The graphite substrate includes at least one of natural graphite, primary particle graphite, secondary particle graphite, needle coke graphite, petroleum coke graphite, green coke graphite, and calcined coke graphite. The asphalt includes β resin, and the content of β resin in the asphalt is 10-80%. Calculated by weight percentage, in the coated graphite, the asphalt accounts for 10-40 wt%, and the graphite substrate accounts for 60-90%.

[0044] In one embodiment, step S1 includes:

[0045] S1.1. Ultrasonically dispersing the asphalt in absolute ethanol for 15-60 min to form an asphalt emulsion.

[0046] By ultrasonically dispersing the asphalt in absolute ethanol, the aggregation state of the asphalt can be effectively destroyed to form a uniform and fine emulsion. This helps to improve the contact uniformity and interfacial bonding force between the asphalt and the graphite substrate in subsequent steps, thus laying a foundation for forming a continuous coating layer.

[0047] S1.2. Transfer the asphalt emulsion to a constant temperature water bath. Under the condition that the temperature is controlled at 40-90 °C, add the graphite substrate to the asphalt emulsion, control the stirring speed at 300-500 rpm, and continuously stir for 1-3 hours until the absolute ethanol completely volatilizes.

[0048] Under the condition of a constant temperature water bath, adding the graphite substrate to the asphalt emulsion and mixing at a moderate stirring speed is conducive to the uniform coating of the asphalt on the graphite surface. Temperature control and stirring uniformity ensure the full volatilization of ethanol, enabling the asphalt to deposit on the graphite surface to form a stable initial coating layer, and improving the stability of subsequent carbonization and the overall structure of the material.

[0049] S1.3. After stirring, transfer it to a vacuum oven and continuously vacuum dry it at a temperature of 60-80°C for 12-24 hours to obtain coated graphite. Drying the mixed material in a vacuum oven can completely remove the residual solvent, and at the same time avoid the thermal degradation and oxidation of asphalt in a low-temperature vacuum environment. The finally formed coated graphite has a uniform and firm asphalt coating layer, which provides a high-quality precursor for subsequent heat treatment and carbonization processes, enhancing the overall conductivity and mechanical stability of the material.

[0050] β-resin is a resin component with excellent film-forming property, adhesiveness and thermal stability, and exists as an active component in asphalt. Its molecular structure is stable, and it can maintain its shape at high temperature and transform into a carbon structure, thus forming a dense carbon layer during the subsequent heat treatment process.

[0051] The advantages of coating graphite substrates by the liquid-phase method are as follows. Ultrasonic dispersion makes the β-resin in the asphalt emulsion disperse evenly, ensuring the formation of a continuous and uniform coating layer on the graphite surface. The temperature-controlled water bath method is conducive to precisely controlling the processes of asphalt deposition and ethanol volatilization, avoiding local overheating or uneven deposition caused by high temperature. Uniform coating can improve the adhesiveness between asphalt and graphite substrates, form a strong interface, and provide a stable precursor for subsequent carbonization. After the formed coating layer is vacuum dried, it is more conducive to generating a dense and highly conductive carbon layer during the carbonization process, thereby optimizing the mechanical and electrochemical properties of the final composite material.

[0052] In one embodiment, step S1 includes:

[0053] S1.1. Preheat the asphalt to 80-120°C and keep stirring for 30-90 minutes, and at the same time add graphene or carbon nanotubes to obtain rheological asphalt.

[0054] Preheating to 80-120°C transforms the asphalt from a high-viscosity solid state into a rheological state, reducing the flow resistance and creating conditions for uniform dispersion. Adding graphene or carbon nanotubes during the stirring process, these highly conductive and mechanical property-enhancing nanomaterials are easily uniformly dispersed at high temperature, thus forming a modified asphalt matrix and improving the conductivity and mechanical strength of the subsequent coating layer. Preheating and sufficient stirring can promote the interaction between the β-resin component in asphalt and the nanomaterials, forming a mixture with better rheological properties and adhesiveness, and providing a better precursor for subsequent solid-phase coating.

[0055] S1.2. Perform solid-phase mixing of the rheological asphalt and graphite substrates in a VC mixer. Set the revolution speed of the VC mixer to 30-150 r / min, the rotation speed to 50-200 r / min, and the mixing time to 0.5-5 hours. During the mixing process, intermittently use ultrasonic-assisted dispersion with a frequency of 20-40 kHz, and the ultrasonic treatment time for each time is 10-20 minutes. After mixing, coated graphite is obtained.

[0056] Utilize solid-phase mixing in a VC mixer. By setting reasonable revolution and rotation speeds (30 - 150 r / min and 50 - 200 r / min) and a mixing time of 0.5 - 5 hours, the modified asphalt and the graphite substrate are fully contacted and evenly dispersed. Intermittently, ultrasonic treatment at 20 - 40 kHz is used for 10 - 20 minutes each time, effectively breaking up the tiny aggregates that may form on the surfaces of the asphalt and graphite, improving the mixing uniformity, and enhancing the interfacial bonding force. After solid-phase mixing, the modified asphalt can uniformly coat the surface of the graphite substrate, forming a continuous and dense coating layer, which is beneficial to the formation of a stable and highly conductive carbon layer during the subsequent heat treatment process.

[0057] Advantages of solid-phase method coating: The combination of a VC mixer and ultrasonic-assisted dispersion effectively overcomes the problem of local unevenness that is prone to occur, making the interfacial contact between the asphalt and graphite closer. Uniform coating can form a continuous precursor layer, which is transformed into a dense carbon layer during the subsequent heat treatment process, thereby improving the overall mechanical strength, conductivity, and cycle stability of the composite material.

[0058] S2. Pass carbon source gas for chemical vapor deposition on the coated graphite to generate a graphite nano-bridging structure with a specific orientation on the surface of the coated graphite, obtaining modified graphite.

[0059] Step S2 includes:

[0060] S2.1. Uniformly lay the coated graphite in a quartz boat, then place the quartz boat in the constant-temperature zone of a tube furnace, evacuate the tube furnace, and introduce an inert gas.

[0061] Uniformly laying the coated graphite in the quartz boat ensures uniform sample distribution; evacuating and introducing high-purity inert gases (such as nitrogen, argon, or hydrogen) in the tube furnace effectively removes air and moisture, creating an oxygen-free and low-impurity reaction environment. Controlling the inert gas flow rate at 1 - 20 L / min helps maintain constant atmosphere pressure and temperature conditions, laying a stable foundation for subsequent chemical vapor deposition (CVD), thus ensuring the uniformity and orientation of the deposited layer.

[0062] S2.2. Increase the temperature to 500 - 1400 °C at a heating rate of 0.5 - 5 °C / min, maintain the temperature, and continuously introduce the carbon source gas for chemical vapor deposition. Adjust the ambient pressure to 10 - 50 Pa, and control the deposition time at 30 - 120 minutes to generate a graphite nano-bridging structure with the same orientation as the gas flow direction. The graphite nano-bridging structure can be 10 - 30 nm.

[0063] The temperature is raised to 500 - 1400°C at a heating rate of 0.5 - 5°C / min. This slow and precise heating method allows the sample to fully adapt to temperature changes during the deposition process, contributing to the formation of a good lattice arrangement. Continuously introduce a carbon source gas (for example: ethylene and hydrogen in a ratio of 2:1, methane and hydrogen in a ratio of 4:1, or acetylene and hydrogen in a ratio of 1:1) and carry out deposition under a controlled low ambient pressure (10 - 50 Pa), which prompts the carbon source molecules to decompose and recombine orderly on the coated graphite surface to form a graphite nanobridging structure with a specific orientation. The deposition time is controlled within 30 - 120 minutes, which can accurately regulate the thickness and structural quality of the deposition layer, ensuring that the generated graphene layer not only has good electrical conductivity but also can provide mechanical support and interface buffering effects.

[0064] In one embodiment, after step S2.2, it further includes:

[0065] Preheat the nitrogen-containing organic precursor at a temperature of 300 - 400°C to obtain a nitrogen-containing organic precursor gas. Maintain the pressure of the tubular furnace and adjust the temperature inside the tubular furnace to 500 - 800°C. Keep the temperature and continuously introduce the nitrogen-containing organic precursor gas for chemical vapor deposition. The deposition time is 1 - 2 hours to form a graphitic carbon nitride thin film on the graphite nanobridging structure. The graphitic carbon nitride thin film can be 10 - 15 nm. The nitrogen-containing organic precursor includes at least one of biuret diamine, urea, cyanamide, guanidine carbonate, and melamine.

[0066] By preheating the nitrogen-containing organic precursor to generate a precursor gas, a uniform and dense graphitic carbon nitride thin film can be formed on the surface of the graphite nanobridging structure. This thin film not only improves the interfacial adhesion but also effectively fills the micropores, enhancing the overall interfacial stability.

[0067] Combined with the oriented graphene bridging structure in step S2.2, it forms a complement with the graphitic carbon nitride thin film. The graphene bridging structure provides a continuous high-conductivity channel, while the graphitic carbon nitride thin film plays a role in interface protection, buffering, and suppressing side reactions, thereby overall enhancing the electron and ion transport performance of the material during rapid charge and discharge. The graphitic carbon nitride thin film has good chemical stability and adhesion. After covering the surface of the graphite nanobridging structure, it can effectively isolate the direct contact between the electrolyte and the active substance, reduce the occurrence of side reactions, and at the same time relieve the stress concentration caused by the volume change of the graphene bridging structure. This double-layer structure significantly improves the stability and cycle life of the electrode material under high-rate and long-cycle conditions.

[0068] Both processes adopt chemical vapor deposition technology, which can precisely control the thickness, crystallinity and orientation of the thin film by finely regulating temperature, heating rate, reaction pressure, gas composition and deposition time. Whether it is the deposition of graphene bridging structure or graphitic carbon nitride thin film, chemical vapor deposition technology can obtain uniform and dense thin films on a large area, ensuring that the final composite material has a continuous and efficient conductive network and a stable interface structure. Both processes are carried out under the protection of inert gas, avoiding oxidation and pollution, and at the same time helping to enhance the adhesion between the deposited thin film and the substrate, improving the overall mechanical stability and durability of the material. The chemical vapor deposition process has high repeatability and large-scale potential, and both of these deposition processes are suitable for the uniform deposition of large-area thin films, providing a reliable technical guarantee for industrial production.

[0069] In order to precisely control the thickness of the graphite nanobridging structure and the graphitic carbon nitride thin film, the control equations are as follows:

[0070] The thickness control equation of the graphite nanobridging structure is:

[0071]

[0072] Where, is the thickness of the graphite nanobridging structure (nm), is the reference thickness of the graphite nanobridging structure (nm), indicating the thickness obtained at the critical temperature and the critical gas pressure under the deposition time of when, is the actual deposition temperature of the graphite nanobridging structure (K), is the actual deposition gas pressure of the graphite nanobridging structure (Pa), t is the deposition time of the graphite nanobridging structure (minutes), is the empirical constant of the graphite nanobridging structure (dimensionless), reflecting the influence of temperature and gas pressure deviation on the deposition rate, is 0.5 - 1.2.

[0073] By controlling the deposition temperature, pressure and deposition time, a graphite nanobridging structure with good orientation and uniform distribution can be effectively formed; an appropriate value can adjust the density and arrangement of the bridging structure under different process conditions, thereby improving the conductivity and mechanical strength of the material; by optimizing the combination of T, P, t, the thickness of the bridging structure can be regulated, thereby adjusting the specific surface area and internal ion diffusion path of the material.

[0074] The thickness control equation of the graphitic carbon nitride thin film is:

[0075]

[0076] Among them, is the thickness (nm) of the graphitic carbon nitride thin film, is the reference thickness (nm) of the graphitic carbon nitride thin film, indicating the thickness obtained at the critical temperature and the critical pressure under the condition that the deposition time is . is the actual deposition temperature (K) of the graphitic carbon nitride thin film, is the actual deposition pressure (Pa) of the graphitic carbon nitride thin film, t is the deposition time (minutes) of the graphitic carbon nitride thin film, is the empirical constant (dimensionless) of the graphitic carbon nitride thin film, reflecting the influence of temperature and pressure deviation on the deposition rate, is 0.8 - 1.5.

[0077] By controlling the deposition temperature and pressure, a uniform and dense graphitic carbon nitride thin film can be effectively formed;

[0078] By appropriately adjusting value, the density and thickness of the thin film can be optimized under different process conditions, pores and defects can be reduced, and the chemical stability and conductivity of the material can be improved.

[0079] By setting the reference temperature and reference pressure, and by using different and values, the deposition thickness of the graphite bridging structure and the carbon nitride thin film can be precisely controlled within the nanometer - scale thickness range. By optimizing and as well as the deposition time t, the growth rate of the bridging structure and the carbon nitride thin film can be matched, and interface defects and stress concentration can be reduced. By reasonably controlling the thickness and orientation, the interface bonding force can be optimized, the electrical conductivity and mechanical stability can be improved, thereby improving the charge - discharge performance and cycle life. By adjusting the deposition parameters, it can adapt to different substrate and gas combinations and is suitable for industrial scale production.

[0080] S2.3. After the deposition is completed, stop introducing the carbon source gas, only introduce the inert gas, keep the temperature for 1 - 20 hours, then slowly cool down to 100 - 800 °C at a cooling rate of 0.5 - 5 °C / min, and then naturally cool down to room temperature to obtain the modified graphite.

[0081] After the deposition is completed, stop introducing the carbon source gas and only introduce the inert gas, and keep it at a high temperature for 1 to 20 hours. This process plays an annealing role, promotes the repair of graphene crystal defects, and enhances its crystallinity and conductivity. Slowly cool the temperature to 100 to 800 °C at a cooling rate of 0.5 to 5 °C / min, and then naturally cool it to room temperature to ensure the slow release of thermal stress and prevent the formation of structural stress concentration and cracks caused by rapid cooling, so as to maintain the integrity and stability of the modified graphite layer. The modified graphite finally obtained through the comprehensive annealing and slow cooling process has a highly ordered, uniform and highly crystalline graphite bridging structure, which significantly improves the overall electrical conductivity, mechanical strength and cycle stability of the material, and has a direct positive impact on the subsequent battery performance.

[0082] The inert gas includes at least one of nitrogen, argon, and hydrogen. The flow rate of the inert gas is 1 to 20 L / min. The carbon source gas includes at least one of ethylene and hydrogen with a volume ratio of 2:1, methane and hydrogen with a volume ratio of 4:1, and acetylene and hydrogen with a volume ratio of 1:1.

[0083] In step S2, by precisely controlling the conditions of chemical vapor deposition, it is possible to promote the nucleation and ordered growth of carbon source molecules on the surface of the coated graphite in a specific direction, thereby forming a graphite nano-bridging structure with a specific orientation. The gas flow direction in the reaction chamber has a guiding effect on the transport of carbon source molecules. A stable laminar flow state and a uniform gas flow rate enable the carbon source molecules to be uniformly deposited along the gas flow direction, thus forming an ordered growth pattern on the substrate. After the coated graphite undergoes pretreatment, its surface has specific micro-roughness and energy distribution, which provides selective deposition sites for carbon atoms. Regions with lower surface energy are more likely to form initial nuclei, and these nuclei will expand along the lowest energy path, ultimately showing a specific orientation. The slow and uniform heating and low-pressure environment in the temperature control system help control the dissociation and deposition rates of carbon source molecules. The lower pressure and uniform temperature field reduce the probability of random deposition, enabling carbon atoms to be orderly arranged on the substrate along a favorable direction.

[0084] The carbon source concentration in the carbon source gas (such as a mixed gas of ethylene, methane or acetylene and hydrogen) and the auxiliary effect of hydrogen are crucial for suppressing the formation of amorphous carbon and promoting the growth of ordered graphene. Hydrogen helps to remove the disordered carbon atoms adsorbed on the surface, which is beneficial to the formation of regular graphene layers. At the same time, the control of the gas flow rate ensures the continuous supply and uniform diffusion of the reactants.

[0085] S3. Prepare a silicon-carbon base material and mix it with the modified graphite to obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0086] Step S3 includes:

[0087] S3.1. Mix the porous carbon precursor with the silicon source material, and under the protection of an inert gas, heat it from room temperature to 400 - 700 °C at a rate of 2 - 5 °C / min, and hold for 2 - 4 hours to obtain a silicon-carbon base material; the porous carbon precursor includes at least one of biomass carbon, pitch carbon, and resin carbon, and the silicon source material includes at least one of sodium silicate, tetraethoxysilane, and nano-silicon powder. Calculated by mass ratio, the porous carbon precursor:silicon source = (2 - 5):1. The silicon-carbon base material includes internal pores and nano-silicon particles located in the internal pores, and the size of the nano-silicon particles is 0.1 - 50 nm, and the size of the internal pores is 0.1 - 100 nm.

[0088] Mixing the porous carbon precursor with the silicon source material according to a mass ratio and heating under the protection of an inert gas can enable the silicon source material to be evenly distributed in the pores of the carbon precursor and partially reduced to form silicon nanoparticles. This not only ensures that the size of the nano-silicon particles is controlled within the range of 0.1 - 50 nm, but also forms a rich porous structure, which is beneficial to the rapid diffusion and storage of lithium ions. During this process, the high specific surface area of the porous carbon precursor provides sufficient dispersion space for the silicon source material, and at the same time helps to construct an efficient conductive network, further improving the overall conductivity and cycle stability of the composite material. By slowly heating and appropriately holding the temperature, the chemical reaction can proceed evenly, avoiding local overheating or agglomeration of the silicon source material, thus ensuring the uniform structure of the silicon-carbon base material and reducing the interfacial stress caused by uneven structure during the subsequent mixing process.

[0089] S3.2. Mix the silicon-carbon base material with modified graphite in a VC mixer according to a specific mass ratio, set the revolution speed of the VC mixer to 20 - 120 r / min and the rotation speed to 40 - 180 r / min, and mix for 0.5 - 4 hours to obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0090] Mix the prepared silicon-carbon base material with modified graphite in a VC mixer. By setting reasonable revolution speed (20 - 120 r / min), rotation speed (40 - 180 r / min) and mixing time (0.5 - 4 hours), it can ensure that the two materials are fully and evenly dispersed at the macroscopic and microscopic levels, forming a tight composite structure. During the mixing process, through mechanical shearing, the possible agglomeration phenomenon on the surface of the materials can be effectively broken, enhancing the interfacial adhesion between silicon-carbon and modified graphite, thereby improving the conductivity and mechanical strength of the overall composite material and optimizing the interfacial stability during the charge and discharge process of the battery. Uniform mixing ensures that the silicon-carbon base material can be evenly dispersed in the graphite matrix, thus forming a continuous and efficient lithium-ion transmission channel during battery operation, while alleviating the volume expansion problem of silicon during charge and discharge, and finally achieving high rate and long cycle life.

[0091] The present invention provides a composite carbon layer-coated graphite-matched silicon-carbon material, which is prepared by a preparation method of the composite carbon layer-coated graphite-matched silicon-carbon material. The composite carbon layer-coated graphite-matched silicon-carbon material includes pitch, a graphite substrate, a graphite nano-bridging structure, and a silicon-carbon substrate; wherein,

[0092] The pitch is used to form a coating carbon layer and optimize the interfacial bonding between the coating carbon layer and the graphite substrate;

[0093] The graphite substrate is used to provide a stable conductive skeleton and structural support;

[0094] The graphite nano-bridging structure is used to strengthen the conductive network, enhance the overall structural stability and conductive performance of the material, and effectively buffer the stress of lithium ions during charge and discharge;

[0095] The silicon-carbon substrate is used to increase the overall theoretical specific capacity of the material and simultaneously buffer the volume expansion of silicon during charge and discharge.

[0096] The following are different embodiments and comparative examples of the present invention.

[0097] Example 1:

[0098] Weigh 0.4 g of pitch with a β-resin content of 40 wt.% and ultrasonically disperse it in 300 mL of absolute ethanol for 30 min. Transfer the solution to a water bath and heat it to 90°C. Add 20 g of graphite (the raw material is needle coke and secondary particles) to the above solution and stir, maintaining 90°C until the absolute ethanol completely evaporates. Transfer the dried material to a vacuum oven for drying. Add the coated sample to a tube furnace, pass nitrogen at a flow rate of 0.2 L / min, heat the carbon source gas to 1250°C at a rate of 2°C / min and hold for 4 h, then pass the nitrogen-containing organic precursor gas and cool down to 800°C, and then cool down naturally. Place the carbonized sample in a VC mixer, add 3 g of the silicon-carbon substrate, and the mixing parameters are as follows: the revolution speed is 60 r / min, the rotation speed is 120 r / min, and mix for 2 h. Obtain the composite carbon layer-coated graphite-matched silicon-carbon material.

[0099] Example 2:

[0100] Weigh 1.2 g of asphalt with a β-resin content of 50 wt.% and disperse it ultrasonically in 300 mL of absolute ethanol for 30 min. Transfer the solution to a water bath and heat it up to 90 °C. Add 20 g of graphite (with petroleum coke and secondary particles as raw materials) to the above solution and stir. Keep it at 90 °C until the absolute ethanol completely evaporates. Transfer the dried material to a vacuum oven for drying. Add the coated sample to a tube furnace, pass nitrogen at a flow rate of 0.2 L / min, heat the carbon source gas to 1200 °C at a rate of 2 °C / min and hold for 4 h, then pass the nitrogen-containing organic precursor gas and cool down to 800 °C, and then cool down naturally. Place the carbonized sample in a VC mixer, add 3 g of silicon-carbon base material, and the mixing parameters are as follows: the revolution speed is 60 r / min, the rotation speed is 120 r / min, and mix for 2 h. Obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0101] Example 3:

[0102] Weigh 10 g of asphalt with a β-resin content of 40 wt.% and disperse it ultrasonically in 3 L of absolute ethanol for 30 min. Transfer the solution to a water bath and heat it up to 90 °C. Add 500 g of graphite (with needle coke and secondary particles as raw materials) to the above solution and stir. Keep it at 90 °C until the absolute ethanol completely evaporates. Transfer the dried material to a vacuum oven for drying. Add the coated sample to a tube furnace, pass nitrogen at a flow rate of 0.2 L / min, heat the carbon source gas to 1250 °C at a rate of 2 °C / min and hold for 4 h, then cool down to 800 °C, and then cool down naturally. Place the carbonized sample in a VC mixer, add 50 g of silicon-carbon base material, and the mixing parameters are as follows: the revolution speed is 60 r / min, the rotation speed is 120 r / min, and mix for 2 h. Obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0103] Example 4:

[0104] Weigh 20 g of asphalt with a β-resin content of 40 wt.% and disperse it ultrasonically in 3 L of absolute ethanol for 30 min. Transfer the solution to a water bath and heat it up to 90 °C. Add 500 g of graphite (with petroleum green coke and primary particles as raw materials) to the above solution and stir. Keep it at 90 °C until the absolute ethanol completely evaporates. Transfer the dried material to a vacuum oven for drying. Add the coated sample to a tube furnace, pass nitrogen at a flow rate of 0.2 L / min, heat the carbon source gas to 1250 °C at a rate of 2 °C / min and hold for 4 h, then cool down to 800 °C, and then cool down naturally. Place the carbonized sample in a VC mixer, add 100 g of silicon-carbon base material, and the mixing parameters are as follows: the revolution speed is 60 r / min, the rotation speed is 120 r / min, and mix for 4 h. Obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

[0105] Example 5:

[0106] Weigh 150 g of asphalt with a β-resin content of 45 wt.% and 5000 g of graphite (raw materials are petroleum coke, primary particles), and place them in a VC mixer. Set the revolution speed of the VC mixer to 50 r / min, the rotation speed to 100 r / min, and the mixing time to 5 h to fully mix the asphalt and graphite. The coated sample is added to a tube furnace, nitrogen is passed at a flow rate of 0.2 L / min, the carbon source gas is introduced, and the temperature is raised to 1250°C at a rate of 2°C / min and held for 4 h, then cooled to 800°C and then cooled naturally. The carbonized sample is placed in a VC mixer, and 500 g of silicon-carbon substrate is added. The mixing parameters are as follows: revolution speed 60 r / min, rotation speed 120 r / min, and mixing for 4 h. A composite carbon layer-coated graphite-matched silicon-carbon material is obtained.

[0107] Comparative Example 1:

[0108] Weigh 20 g of graphite (raw materials are needle coke, secondary particles) and place it in a VC mixer, add 3 g of silicon-carbon substrate. The mixing parameters are as follows: revolution speed 60 r / min, rotation speed 120 r / min, and mixing for 2 h. An uncoated graphite-matched silicon-carbon material is obtained.

[0109] Electrochemical performance test:

[0110] Electrode fabrication: Weigh the above composite material, conductive carbon black, and binder CMC in proportion, add deionized water to prepare a uniform slurry. The solid content ratio of the composite material: conductive carbon black: binder CMC is 95:1.5:3.5. Use a homogenizer to prepare the sample, with a rotation speed of 2000 rpm and a time of 20 min.

[0111] After passing the slurry through a sieve, it is evenly coated on a copper foil and placed in a vacuum drying oven at 90°C for drying. After drying, the electrode sheet is roll-pressed and cut into circular electrodes of a certain size, and the electrode mass is recorded.

[0112] Button cell assembly: In an argon atmosphere glove box, using a lithium metal sheet as the counter electrode, assemble it with the above-obtained electrode, separator, gasket, etc. into a button cell, and use a special electrolyte for silicon-carbon as the electrolyte.

[0113] The data results are summarized in Table 1. It can be seen that the composite carbon layer-coated graphite-matched silicon-carbon material provided in Example 2 has an initial reversible capacity of 533.6 mAh / g, an initial Coulombic efficiency of 93.03%. After 100 cycles, the reversible capacity is 489.4 mAh / g, and the capacity retention rate is 91.72%, showing excellent cycle performance and initial cycle Coulombic efficiency.

[0114] Table 1: Performance test results of examples and comparative examples

[0115]

[0116] Figure 1 TEM image of the composite carbon layer-coated graphite matching silicon-carbon material. The interlayer distance and the clarity of the stacking structure reflect the crystallinity and orientation of the material.

[0117] Figure 2 X-ray diffraction (XRD) patterns of the material under different experimental conditions. There are multiple characteristic diffraction peaks in the XRD patterns, indicating that the material has a highly ordered crystal structure. The positions of the diffraction peaks can determine the lattice constant, crystallinity, and orientation of the material. The displacement or intensity change of the XRD peaks of different samples illustrates the regulation effect of different deposition conditions on the material structure. The diffraction peaks of Examples 1-5 are sharp, indicating that the material has higher crystallinity. The peak positions are stable, and the intervals between the diffraction peaks are uniform, indicating that the material structure is complete. The higher diffraction peak intensity indicates that the material has higher orientation and better interlayer stacking. The diffraction peak intensity of Comparative Example 1 is lower, indicating that there are more disorders or defects inside the material.

[0118] Figure 3 Raman spectra of the materials obtained under different experimental conditions are shown. The Raman spectra contain a D peak (located at about 1350 cm⁻¹) and a G peak (located at about 1580 cm⁻¹). The and ratios marked in the figure represent the graphitization degree and defect degree of the material. The of Comparative Example 1 is too low, indicating that the overall graphitization degree of the material is poor and the D peak is weak. The of Comparative Example 1 is too low. An appropriate amount of defects in graphene or graphite materials can introduce more electron migration paths into the material structure and provide active sites for the diffusion of lithium ions. of Comparative Example 1 is too low. Although the material structure integrity and mechanical strength are higher, the electron / ion migration rate may be limited. By comparing the ratios between different samples, the influence of preparation conditions on the material structure integrity and the number of defects can be judged. Examples 1–5 all show obvious G peaks and D peaks, indicating that the material has a graphite or graphene structure. The D peak and G peak signals of the comparative example are very weak, indicating that the material structure has serious defects, a large amount of disordered stacking appears, and the graphitization degree is poor.

[0119] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material, characterized in that the steps include: S1, coating asphalt on a graphite substrate to obtain coated graphite; S2, introducing a carbon source gas to perform chemical vapor deposition on the coated graphite, generating a graphite nano-bridge structure with a specific orientation on the surface of the coated graphite, and obtaining modified graphite; Step S2 includes: S2.1, the coated graphite is evenly laid in a quartz boat, and then the quartz boat is placed in a constant temperature zone of a tube furnace, the tube furnace is evacuated, and an inert gas is introduced; S2.2, raising the temperature to 500-1400°C at a heating rate of 0.5-5°C / min, maintaining the temperature and continuously introducing carbon source gas for chemical vapor deposition, adjusting the ambient pressure to 10-50Pa, controlling the deposition time to 30-120 minutes, generating a graphite nano-bridge structure oriented in the same direction as the gas flow, preheating the nitrogen-containing organic precursor at a preheating temperature of 300-400°C, obtaining a nitrogen-containing organic precursor gas, maintaining the pressure of the tubular furnace and adjusting the temperature in the tubular furnace to 500-800°C, maintaining the temperature and continuously introducing the nitrogen-containing organic precursor gas for chemical vapor deposition, the deposition time being 1-2 hours, generating a graphite phase carbon nitride film on the graphite nano-bridge structure, wherein the graphite phase carbon nitride film is 10-15nm, and the nitrogen-containing organic precursor comprises at least one of diurea diamine, urea, cyanamide, guanidine carbonate, and melamine; S2.3, after the deposition is completed, stop introducing the carbon source gas, introduce only the inert gas, keep the temperature for 1 to 20 hours, then slowly cool down to 100 to 800°C at a cooling rate of 0.5 to 5°C / min, and then naturally cool down to room temperature to obtain modified graphite; S3, preparing a silicon-carbon substrate and mixing it with the modified graphite to obtain a composite carbon layer-coated graphite-matched silicon-carbon material.

2. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: In step S2, The thickness control equation of the graphite nano-bridge structure is: in, is the thickness of the graphene nano-bridge structure, is the reference thickness of the graphene nano-bridge structure, indicating the critical temperature and critical pressure The deposition time is The thickness obtained when is the actual deposition temperature of the graphene nano-bridge structure, is the actual deposition pressure of the graphite nano-bridge structure, t is the deposition time of the graphite nano-bridge structure, is the empirical constant of graphene nano-bridge structure, reflecting the effect of temperature and pressure deviation on deposition rate. 0.5~1.2; The thickness control equation of graphite phase carbon nitride film is: in, is the thickness of graphite carbon nitride film, is the reference thickness of graphite phase carbon nitride film, indicating the critical temperature and critical pressure The deposition time is The thickness obtained when is the actual deposition temperature of graphite phase carbon nitride film, is the actual deposition pressure of graphite phase carbon nitride film, t is the deposition time of graphite phase carbon nitride film, is the empirical constant of graphite phase carbon nitride film, reflecting the effect of temperature and pressure deviation on deposition rate. It is 0.8~1.

5.

3. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: In step S1, the graphite substrate includes at least one of natural graphite, primary graphite particles, secondary graphite particles, needle coke graphite, petroleum coke graphite, raw coke graphite, and cooked coke graphite, and the asphalt includes β resin, and the content of the β resin in the asphalt is 10-80%.

4. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: Step S1 includes: S1.

1. Ultrasonic dispersion of asphalt in anhydrous ethanol for 15 to 60 minutes to form an asphalt emulsion; S1.2, transfer the asphalt emulsion to a constant temperature water bath, add the graphite substrate to the asphalt emulsion under the condition of controlling the temperature at 40-90°C, control the stirring speed at 300-500 rpm, and continue stirring for 1-3 hours until the anhydrous ethanol is completely evaporated; S1.

3. After stirring, transfer to a vacuum oven and continue vacuum drying at 60-80°C for 12-24 hours to obtain coated graphite.

5. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: Step S1 includes: S1.1, preheating the asphalt to 80-120°C and stirring for 30-90 minutes, while adding graphene or carbon nanotubes to obtain rheological asphalt; S1.

2. The rheological asphalt and the graphite substrate are mixed in the solid phase in a VC mixer. The revolution speed of the VC mixer is set to 30-150 r / min, the rotation speed is set to 50-200 r / min, and the mixing time is set to 0.5-5 hours. During the mixing process, ultrasonic assisted dispersion with a frequency of 20-40 kHz is intermittently used. The ultrasonic treatment time for each time is 10-20 minutes. After the mixing is completed, the coated graphite is obtained.

6. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 4 or 5, characterized in that: Calculated by weight percentage, in the coated graphite, the asphalt accounts for 10-40wt%, and the graphite substrate accounts for 60-90%.

7. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: In step S2, the inert gas includes at least one of nitrogen, argon, and hydrogen, the flow rate of the inert gas is 1~20L / min, and the carbon source gas includes at least one of ethylene and hydrogen in a volume ratio of 2:1, methane and hydrogen in a volume ratio of 4:1, and acetylene and hydrogen in a volume ratio of 1:

1.

8. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 1, characterized in that: Step S3 includes: S3.1, mixing the porous carbon precursor with the silicon source material, raising the temperature to 400-700°C at 2-5°C / min under the protection of an inert gas, and keeping the temperature for 2-4 hours to obtain a silicon-carbon substrate; S3.

2. Mix the silicon-carbon substrate and the modified graphite in a VC mixer at a specific mass ratio, set the VC mixer revolution speed to 20-120 r / min, rotation speed to 40-180 r / min, mix for 0.5-~4 hours, and obtain a composite carbon layer-coated graphite matching silicon-carbon material.

9. The method for preparing a composite carbon layer-coated graphite-matched silicon-carbon material according to claim 8, characterized in that: In step S3, the porous carbon precursor includes at least one of biomass carbon, asphalt carbon, and resin carbon, and the silicon source material includes at least one of sodium silicate, tetraethoxysilane, and nano-silicon powder. Calculated by mass ratio, the porous carbon precursor: the silicon source = (2~5): 1, and the silicon-carbon substrate includes internal pores and nano-silicon particles located in the internal pores. The size of the nano-silicon particles is 0.1~50nm, and the size of the internal pores is 0.1~100nm.

10. A composite carbon layer coated graphite matching silicon-carbon material, characterized in that: It is made by the preparation method of the composite carbon layer coated graphite matching silicon-carbon material according to any one of claims 1 to 9, wherein the composite carbon layer coated graphite matching silicon-carbon material comprises asphalt, a graphite substrate, a graphite nano-bridge structure, and a silicon-carbon substrate; wherein, The pitch is used to form a coated carbon layer and optimize the interface bonding between the coated carbon layer and the graphite substrate; The graphite substrate is used to provide a stable conductive skeleton and structural support; The graphite nano-bridge structure is used to strengthen the conductive network, enhance the overall structural stability and conductive properties of the material, and effectively buffer the stress of lithium ions during the charging and discharging process; The silicon-carbon substrate is used to increase the theoretical specific capacity of the entire material and buffer the volume expansion of silicon during the charge and discharge process.

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