Silicon-carbon composite material, preparation method and application thereof

Abstract

The application belongs to the field of battery materials, and discloses a silicon-carbon composite material, a preparation method and application thereof. The silicon-carbon composite material comprises a porous carbon matrix, silicon particles, silicon nanowires and a hard carbon layer. The silicon particles are distributed in the pores of the porous carbon matrix and are bonded to the porous carbon matrix through Si-O-C chemical bonds. The silicon nanowires grow on the surface of the porous carbon matrix, and the surface layer of the silicon nanowires is carburized to form silicon carbide. The hard carbon layer at least coats part of the surface of the particles formed by the porous carbon matrix, the silicon particles and the silicon nanowires. The silicon-carbon composite material provided by the application realizes step-by-step effective regulation of the volume expansion of silicon at the microscale through a multi-stage synergistic mechanism, establishes a radial grading stress management network from the inside of the particles to the surface, and significantly reduces the overall volume expansion rate of the material. The silicon-carbon composite material realizes the synergistic consideration of high specific capacity, low volume expansion, long cycle life and excellent rate characteristics.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and relates to a negative electrode material, specifically a silicon-carbon composite material and its preparation method and application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems. Silicon, with its extremely high theoretical specific capacity (approximately 4200 mAh / g), is considered one of the most promising candidate materials to replace traditional graphite anodes. However, silicon undergoes significant volume expansion (>300%) during lithium insertion / extraction, leading to pulverization of active particles, damage to the electrode structure, and repeated rupture of the solid electrolyte interface film. This ultimately results in rapid capacity decay, severely limiting its commercial application.

[0003] To alleviate the volume expansion of silicon, existing technologies mainly employ silicon-carbon composite strategies. Common approaches include dispersing nano-silicon in a porous carbon matrix, constructing a silicon core-carbon shell structure, or coating the silicon surface with carbon. However, these approaches still have inherent drawbacks: (1) Silicon and carbon matrix are mostly physically mixed or simply attached, resulting in insufficient interfacial bonding strength, and silicon particles are prone to detaching from the conductive network during cycling; (2) A single carbon coating layer lacks internal stress buffer design, and is prone to through-cracks under repeated silicon expansion, thus losing its protective function; (3) When pursuing high silicon content, the structure lacks reserved expansion space, leading to concentrated release of expansion stress and accelerating material failure. Summary of the Invention

[0004] Addressing the shortcomings and deficiencies of existing technologies: In a first aspect, the present invention provides a silicon-carbon composite material, comprising a porous carbon matrix, silicon particles, silicon nanowires, and a hard carbon layer; The silicon particles are distributed within the pores of the porous carbon matrix; and the silicon particles are bonded to the porous carbon matrix through Si-OC chemical bonds, and the particles formed by the silicon particles and the porous carbon matrix are the first intermediate particles. The silicon nanowires at least cover a portion of the surface of the first intermediate particle; the surface of the silicon nanowires is infiltrated with carbide to form amorphous silicon carbide, and the particle composed of the first intermediate particle and the silicon nanowires is the second intermediate particle. The hard carbon layer covers at least a portion of the surface of the second intermediate particle.

[0005] Preferably, the total mass content of silicon in the silicon-carbon composite material is 40wt% to 60wt%.

[0006] Preferably, the specific surface area of ​​the silicon-carbon composite material is 0.5~8m². 2 / g.

[0007] Preferably, the resistivity of the silicon-carbon composite material powder is 10~80 Ω·cm.

[0008] Preferably, the ratio of the volume of the silicon particles to the total pore volume of the porous carbon matrix is ​​0.3 to 0.7.

[0009] Preferably, the porous carbon matrix has a D50 of 2~8 μm and a pore volume of 0.5~1.0 cm³. 3 / g.

[0010] Preferably, the silicon nanowire has an average length of L and an average width of D, where 10 ≤ L / D ≤ ​​200.

[0011] Further optimization is achieved by setting L to 100 nm to 2 μm and D to 10 to 100 nm.

[0012] Preferably, the silicon nanowire coating area is Sn, and the surface area of ​​the first intermediate particle is Sc, where 0.3 ≤ Sn / Sc ≤ 0.9.

[0013] Secondly, the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps: Step 1, Surface functionalization: Ozone oxidation treatment of porous carbon matrix; Step 2, silicon deposition: The product from Step 1 is subjected to vapor phase deposition by introducing a mixture of silane and carrier gas to deposit silicon, thereby obtaining the first intermediate particles. Step 3, silicon nanowire growth: silicon nanowires are grown on the surface of the first intermediate particle by introducing a silane-carrier gas mixture through chemical vapor deposition to obtain the second intermediate particle. Step 4, carburizing to form an amorphous silicon carbide layer: The second intermediate particles are treated by chemical vapor deposition, and an acetylene-carrier gas mixture is introduced. The silicon nanowires are transformed in situ through the carburizing reaction to form an amorphous silicon carbide layer, thus obtaining the intermediate phase material. Step 5, Deposit hard carbon layer: Deposit hard carbon layer on the surface of mesophase material using chemical vapor deposition process, introduce acetylene-carrier gas mixture to deposit hard carbon layer on the surface of mesophase material, thus obtaining the silicon-carbon composite material.

[0014] Preferably, the porous carbon matrix used in step 1 is obtained by carbonizing and activating a carbon source precursor; the carbon source precursor is any one or more of phenolic resin, epoxy resin, polyacrylonitrile, asphalt, glucose, sucrose, cellulose and its derivatives, coconut shell, and fruit shell; the porous carbon matrix obtained after carbonizing and activating the carbon source precursor has a D50 of 2~8μm and a pore volume of 0.5~1.0cm³. 3 / g.

[0015] Preferably, in step 1, the surface functionalization process specifically involves: placing the porous carbon matrix in an ozone reactor, introducing a mixture of ozone and oxygen, controlling the ozone volume concentration to be 1%~10%, the gas flow rate to be 20~100 sccm, the reaction temperature to be 15~60℃, and the reaction time to be 10~40 min, thereby introducing oxygen-containing functional groups onto the surface of the porous carbon matrix.

[0016] Preferably, in step 2, the volume ratio of silane to carrier gas in the reaction system is 1:(2~10), the partial pressure of silane in the reaction system is 1~5kPa, the deposition temperature is 450~600℃, and the deposition time is 2~6h.

[0017] Preferably, in step 3, the silicon nanowire growth process specifically involves: depositing nano-metal catalytic particles as a catalyst on the surface of the first intermediate particle, and then growing silicon nanowires by introducing a silane-carrier gas mixture through a chemical vapor deposition process.

[0018] Preferably, in step 3, the silicon nanowire growth process employs oxygen-assisted PECVD (oxygen-assisted plasma-enhanced chemical vapor deposition) to deposit silicon nanowires.

[0019] Preferably, in step 4, the flow rate of the acetylene-carrier gas mixture is 50~200 sccm, the volume ratio of acetylene to carrier gas in the mixture is 1:(2~5), the carburizing temperature is 650~800℃, and the carburizing time is 10~30 min.

[0020] Preferably, in step 5, when preparing the hard carbon coating layer using chemical vapor deposition, a mixture of acetylene and carrier gas is continuously introduced into the reaction system. The flow rate of the acetylene-carrier gas is 50~300 sccm, the volume ratio of acetylene to carrier gas in the mixture is 1:(2~10), the deposition temperature is 400~550℃, and the deposition time is 1~4h.

[0021] Thirdly, the present invention provides a battery comprising the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0022] Compared with the prior art, one or more technical solutions provided by the present invention have at least one of the following beneficial effects: (1) The silicon-carbon composite material provided by the present invention achieves effective control of silicon volume expansion at the microscale through a multi-level synergistic mechanism of "chemical anchoring - one-dimensional flexible release - strong interface transition". The silicon particles, silicon nanowires, amorphous silicon carbide layer and hard carbon layer establish a radial hierarchical stress management network from the inside of the particles to the surface, which significantly reduces the overall volume expansion rate of the material; and greatly reduces the irreversible consumption of active lithium, and significantly improves the first coulombic efficiency; the four achieve a synergistic balance of high specific capacity, low volume expansion, long cycle life and excellent rate performance.

[0023] (2) Further optimize the silicon content in the silicon-carbon composite material, control the pore volume ratio of silicon particles and porous carbon matrix, the length and width parameters of silicon nanowires, and the coating area of ​​silicon nanowires, so as to further improve the electrochemical performance of the silicon-carbon composite material provided by the present invention. Attached Figure Description

[0024] Figure 1 A schematic diagram of a cross-sectional structure of the silicon-carbon composite material provided by the present invention; Figure 2 This is a cross-sectional electron microscope image of the silicon-carbon composite material prepared in Example 1; Figure 3 , Figure 4 This is an electron microscope image of the surface of the silicon-carbon composite material prepared in Example 1.

[0025] 1. Porous carbon matrix; 2. Silicon particles; 3. Silicon nanowires; 4. Hard carbon layer. Detailed Implementation

[0026] The present invention provides the following specific technical solutions.

[0027] In a first aspect, the present invention provides a silicon-carbon composite material, comprising a porous carbon matrix, silicon particles, silicon nanowires, and a hard carbon layer; The silicon particles are distributed within the pores of the porous carbon matrix; and the silicon particles are bonded to the porous carbon matrix through Si-OC chemical bonds, and the particles formed by the silicon particles and the porous carbon are the first intermediate particles. The silicon nanowires at least cover a portion of the surface of the first intermediate particle; the surface of the silicon nanowires is infiltrated with carbide to form amorphous silicon carbide, and the particle composed of the first intermediate particle and the silicon nanowires is the second intermediate particle. The hard carbon layer covers at least a portion of the surface of the second intermediate particle.

[0028] Figure 1 The diagram shows the structure of the silicon-carbon composite material provided by the present invention. The main body of the silicon-carbon composite material is a porous carbon matrix 1, in which multiple channels are distributed. Silicon particles 2 are distributed in the channels, silicon nanowires 3 are distributed on the surface of the porous carbon matrix 1, and a hard carbon layer 4 is coated on the outermost layer.

[0029] Research has revealed that the silicon-carbon composite material with a gradient silicon layer provided by this invention achieves effective step-by-step control of silicon volume expansion at the microscale through a multi-level synergistic mechanism of "chemical anchoring, one-dimensional flexible release, and strong interfacial transition," and has the following outstanding advantages: Silicon particles form Si-OC chemical bonds with the pore walls of the carbon matrix through in-situ chemical vapor deposition, solving the problem of silicon easily detaching from the conductive network in traditional physical filling. Silicon nanowires on the porous carbon matrix surface utilize the unique bending, twisting, and gap-accommodating capabilities of one-dimensional materials to transform anisotropic expansion stress into flexible deformation release, avoiding stress concentration and pulverization. Furthermore, silicon nanowires and silicon particles are integrated through lattice continuity or Si-Si bonds, eliminating the potential for physical interface delamination between inner and outer silicon layers. Amorphous silicon carbide formed by carburizing silicon nanowires has both chemical bonding interface and modulus transition functions. The amorphous silicon carbide (inner high-modulus brittle layer) and hard carbon layer (outer low-modulus tough layer) form a gradient matching structure from high modulus to low modulus and from brittle to tough. The inner side provides rigid mechanical constraints to maintain structural integrity, while the outer side absorbs and releases expansion stress through flexible deformation and avoids interlayer delamination and brittle fracture. This not only inhibits excessive expansion of silicon nanowires and alleviates stress abrupt changes, but also achieves seamless stress transfer from internal rigid constraints to external flexible buffers. The four components work together to establish a radially graded stress management network from the particle interior to the surface, significantly reducing the overall volumetric expansion rate of the material. This structure achieves a synergistic balance of high specific capacity, low volumetric expansion, long cycle life, and excellent rate capability.

[0030] Preferably, the total mass content of silicon in the silicon-carbon composite material is 40wt% to 60wt%.

[0031] Research has shown that controlling the total silicon content between 40wt% and 60wt% can ensure the high specific capacity of composite materials by relying on high silicon content, while avoiding the severe volume expansion, structural collapse and cycle decay caused by excessive silicon content, thus balancing high capacity, low expansion and long cycle performance.

[0032] Preferably, the specific surface area of ​​the silicon-carbon composite material is 0.5~8m². 2 / g.

[0033] Studies have shown that this specific surface area can reduce electrolyte side reactions, stabilize the SEI membrane, and simultaneously ensure ion transport efficiency, balancing cycle stability and rate performance.

[0034] Preferably, the resistivity of the silicon-carbon composite material powder is 10~80 Ω·cm.

[0035] Research has shown that by relying on an integrated conductive network consisting of a porous carbon matrix, continuous Si-Si bonded silicon nanowires, gradient silicon carbide, and hard carbon coating, a continuous electron transport pathway can be constructed, effectively reducing interfacial contact impedance. This avoids both excessively high resistivity leading to poor conductivity and increased polarization, and excessively low resistivity causing overly dense particles and hindered ion transport, thus synergistically improving the material's conductivity and electrochemical kinetics.

[0036] Preferably, the ratio of the volume of the silicon particles to the total pore volume of the porous carbon matrix is ​​0.3 to 0.7.

[0037] Research has shown that the optimal ratio of silicon particle volume to the total pore volume of the porous carbon matrix is ​​0.3 to 0.7. Combining the four-level gradient structure of porous carbon matrix, internally anchored silicon particles, surface silicon nanowires, amorphous silicon carbide, and hard carbon layer, this structure can not only utilize the carbon channels to reasonably reserve expansion buffer space and exert the rigid confinement effect within the inner pores to prevent excessive filling of silicon particles from cracking the carbon matrix, but also match a multi-level synergistic system of flexible expansion of outer silicon nanowires, tough interface of silicon carbide transition layer, and protection of hard carbon outer layer. This ensures high overall silicon capacity while progressively buffering stress, maintaining the integrity of the overall structure, and balancing the material's cycle stability and electrochemical capacity.

[0038] Preferably, the porous carbon matrix has a D50 of 2~8 μm and a pore volume of 0.5~1.0 cm³. 3 / g.

[0039] Preferably, the silicon nanowire has an average length of L and an average width of D, where 10 ≤ L / D ≤ ​​200.

[0040] Research has revealed that the optimized parameters of the aforementioned silicon nanowires are well-suited to a multi-level gradient stress buffer and structural stability design. This design endows the silicon nanowires with one-dimensional flexible deformation capabilities to efficiently release the anisotropic expansion stress of silicon, avoiding stress concentration caused by excessively short and thick wires or bending, breakage, and agglomeration caused by excessively long and thin wires. It also ensures the strong Si-Si covalent bond connection between the nanowires and the substrate silicon particles, reducing the risk of interlayer delamination and conductive network breakage. Furthermore, it is compatible with the uniform deposition of subsequent coating layers, ensuring the integrity of the protective layer to stabilize the SEI film and reduce lithium loss. Under the premise of not over-stabilizing, it increases the silicon loading capacity, achieving a synergistic balance of high specific capacity, low volume expansion, long cycle life, and excellent rate performance, which aligns with the multi-level synergistic mechanism of "chemical anchoring, one-dimensional flexible release, and strong interfacial transition".

[0041] Further optimization is achieved by setting L to 100 nm to 2 μm and D to 10 to 100 nm.

[0042] Preferably, the silicon nanowire coating area is Sn, and the surface area of ​​the first intermediate particle is Sc, where 0.3 ≤ Sn / Sc ≤ 0.9.

[0043] Research has shown that controlling the ratio of silicon nanowire coating area to the surface area of ​​the first intermediate particle to be between 0.3 and 0.9, combined with a multi-level structure of porous carbon-intrapore silicon particles-silicon nanowires-amorphous silicon carbide-hard carbon, can both leverage the moderately coated silicon nanowires to perform one-dimensional flexible expansion and construct ion-conducting channels, and retain reasonable exposed interfaces to facilitate the uniform composite coating of subsequent silicon carbide and hard carbon layers. This avoids insufficient stress relief and incomplete conductive network due to insufficient coating, while preventing excessive coating from clogging pores and limiting silicon expansion buffer space. The synergistic effect of inner carbon pore confinement, intermediate tough transition layer and outer hard carbon protection achieves synergistic optimization of structural stability, rate performance and cycle life.

[0044] Preferably, the ratio of the mass of silicon in the first intermediate particle to the mass of silicon in the second intermediate particle is (0.7~0.9):1.

[0045] Secondly, the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps: Step 1, Surface functionalization: Ozone oxidation treatment of porous carbon matrix; Step 2, silicon deposition: The product from Step 1 is subjected to vapor phase deposition by introducing a mixture of silane and carrier gas to deposit silicon, thereby obtaining the first intermediate particles. Step 3, silicon nanowire growth: silicon nanowires are grown on the surface of the first intermediate particle by introducing a silane-carrier gas mixture through chemical vapor deposition to obtain the second intermediate particle. Step 4, carburizing to form an amorphous silicon carbide layer: The second intermediate particles are treated by chemical vapor deposition, and an acetylene-carrier gas mixture is introduced. The silicon nanowires are transformed in situ through the carburizing reaction to form an amorphous silicon carbide layer, thus obtaining the intermediate phase material. Step 5, Deposit hard carbon layer: Deposit hard carbon layer on the surface of mesophase material using chemical vapor deposition process, introduce acetylene-carrier gas mixture to deposit hard carbon layer on the surface of mesophase material, thus obtaining the silicon-carbon composite material.

[0046] Preferably, the porous carbon matrix used in step 1 is obtained by carbonizing and activating a carbon source precursor; the carbon source precursor is any one or more of phenolic resin, epoxy resin, polyacrylonitrile, asphalt, glucose, sucrose, cellulose and its derivatives, coconut shell, and fruit shell; the porous carbon matrix obtained after carbonizing and activating the carbon source precursor has a D50 of 2~8μm and a pore volume of 0.5~1.0cm³. 3 / g.

[0047] In actual production, porous carbon substrates can be purchased through commercial channels or obtained by carbonizing and activating the aforementioned carbon source precursors, and then sieving to obtain porous carbon substrates with pore size, pore volume and pore structure that are adapted to the subsequent silicon loading and confinement requirements, providing an ideal carrier for silicon particle anchoring deposition and multi-level composite structure construction.

[0048] Preferably, in step 1, the surface functionalization process specifically involves: placing the porous carbon matrix in an ozone reactor, introducing a mixture of ozone and oxygen, controlling the ozone volume concentration to be 1%~10%, the gas flow rate to be 20~100 sccm, the reaction temperature to be 15~60℃, and the reaction time to be 10~40 min, thereby introducing oxygen-containing functional groups onto the surface of the porous carbon matrix.

[0049] Research has shown that this ozone oxidation parameter can mildly and controllably introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups uniformly into the inner walls and surface of porous carbon matrix channels. This can efficiently provide active binding sites for subsequent silicon particles, promote the stable bonding and anchoring of Si-OC chemical bonds, strengthen the bonding force of carbon-silicon interface, prevent silicon from falling off the conductive network, and optimize interface wettability, thus laying a good interface foundation for the subsequent construction of multi-level composite structures.

[0050] Preferably, in step 2, the volume ratio of silane to carrier gas in the reaction system is 1:(2~10), the partial pressure of silane in the reaction system is 1~5kPa, the deposition temperature is 450~600℃, and the deposition time is 2~6h.

[0051] Research has shown that a lower silane partial pressure can slow down the pyrolysis rate, which is conducive to the diffusion and nucleation of silicon atoms into the porous carbon channels, avoiding accumulation only on the surface. Controlling the silane partial pressure can maintain a stable precursor concentration and prevent it from being carried away by the gas flow before it has fully reacted. The deposition temperature can ensure effective pyrolysis of silane and protect the stability of the porous carbon framework structure. By coordinating the deposition time with the temperature, the amount of silicon filling in the pores can be precisely controlled, so that the ratio of silicon volume to the total pore volume of porous carbon is maintained at 0.3~0.7. This ensures high capacity while reserving sufficient expansion buffer space, providing a structural basis for subsequent multi-stage stress control.

[0052] Preferably, in step 3, the silicon nanowire growth process specifically involves: depositing nano-metal catalytic particles as a catalyst on the surface of the first intermediate particle, and then growing silicon nanowires by introducing a silane-carrier gas mixture through a chemical vapor deposition process.

[0053] Preferably, in step 3, the nano-metal catalytic particles are any one or more of Au, Sn, In, and Ga.

[0054] Research has shown that Au, Sn, In, and Ga metals can all form eutectic alloy droplets with silicon. By utilizing metal nanoparticles to form liquid microregions with silicon, silicon atoms are adsorbed from the gas. When supersaturated, crystals precipitate from the liquid-solid interface, and silicon nanowires are continuously grown.

[0055] Further optimization involves depositing nano-metal catalytic particles on the surface of the first intermediate particle using either radio frequency plasma deposition or impregnation-thermal reduction; then continuously introducing a silane-argon mixture to grow silicon nanowires; the volume ratio of silane to argon is 1:(2~10), the partial pressure of silane in the reaction system is 1~5 kPa, the deposition temperature is 400~550℃, and the deposition time is 15~50 min, thereby growing silicon nanowires on the surface of the first intermediate particle.

[0056] In actual production, the radio frequency plasma deposition process is as follows: the first intermediate particle is placed in the radio frequency plasma deposition chamber for deposition, and a metal target material (Au, Sn, In, Ga) with a purity higher than 99.99% is selected. The sputtering power is controlled at 50~150W, the sputtering time is 30~120s, and the sputtering temperature is 20~200℃.

[0057] When using the impregnation-thermal reduction method, the first intermediate particles are immersed in a metal salt solution, stirred and filtered sequentially, then vacuum dried at 50~80℃, and then heat-treated at 300~500℃ for 1~3h in an H2-Ar mixed atmosphere (H2 volume fraction of 3vol%~8vol%) to reduce the metal salt into nano-metal catalytic particles.

[0058] Radio frequency plasma deposition is a physical method that uses high-energy argon ions to bombard a metal target, causing atoms to adhere to the substrate surface. The resulting nano-metal catalytic particles have high purity and extremely uniform particle size, but weak bonding force. The impregnation-thermal reduction method is a chemical method that uses metal salt solution to impregnate the particles and then reduces them at high temperature with hydrogen, allowing the particles to grow in situ from the substrate surface and become tightly anchored. The particles have strong bonding force and can penetrate into the interior of porous carriers, resulting in high loading capacity.

[0059] Preferably, in step 3, the silicon nanowire growth process employs oxygen-assisted PECVD (oxygen-assisted plasma-enhanced chemical vapor deposition) to deposit silicon nanowires.

[0060] In actual production, oxygen-assisted PECVD deposition of silicon nanowires specifically involves: placing the first intermediate particle in a plasma-enhanced chemical vapor deposition chamber, controlling the oxygen concentration in the reaction chamber to be 0.1 vol%~0.5 vol%, the power of the radio frequency plasma power supply to be 200~300 W, the deposition temperature in the reaction chamber to be 500~600 °C, controlling the partial pressure of silane in the reaction chamber to be 6~8 kPa, and the deposition time to be 0.5~1 h.

[0061] Research has revealed that the process of first depositing nano-metal catalyst particles and then growing silicon nanowires is a "metal catalysis + gas-liquid-solid (VLS) mechanism." This requires pre-loading nano-metals such as Au and Sn onto the particle surface as catalysts, followed by the introduction of silane for silicon nanowire growth. The metal and silicon form eutectic droplets, thus directionally growing the nanowires. This method offers good controllability, high crystallinity, and uniform diameter. Oxygen-assisted PECVD deposition does not require an external metal catalyst; silane and oxygen are directly introduced into the PECVD chamber, and silicon nanowires are grown through an oxide-assisted mechanism under plasma conditions. This process is simpler, but the growth temperature is slightly higher, and the uniformity of nanowire diameter and orientation is generally slightly inferior to the metal-catalyzed VLS method. This invention focuses on achieving high crystallinity, controllable diameter, and tolerance to trace metal impurities, preferably using a metal-catalyzed VLS process combined with vapor deposition to prepare silicon nanowires.

[0062] Preferably, in step 4, the flow rate of the acetylene-carrier gas mixture is 50~200 sccm, the volume ratio of acetylene to carrier gas in the mixture is 1:(2~5), the carburizing temperature is 650~800℃, and the carburizing time is 10~30 min.

[0063] Research has shown that at 650-800℃, the active carbon atoms produced by acetylene cracking react chemically with silicon atoms on the surface of silicon nanowires to form silicon carbide. In actual production, the thickness of the amorphous silicon carbide layer is determined by the carburizing process parameters. By controlling the carburizing process, the thickness of the amorphous silicon carbide layer can be controlled. Under the above-mentioned optimized carburizing process, only the outer exposed area of ​​the silicon nanowire is carburized to transform into amorphous silicon carbide to adapt to silicon lithium intercalation / deintercalation deformation, effectively buffering interlayer stress and strengthening the interface bonding between the silicon phase and the outer hard carbon layer. A moderate thickness can form a complete and dense barrier layer to isolate the electrolyte and stabilize the SEI film, without hindering ion conduction and reducing the overall silicon capacity due to excessive thickness, or causing insufficient protection and interface reinforcement due to excessive thinness. This synergistically achieves structural toughness, interface stability, and excellent electrochemical performance.

[0064] Preferably, in step 5, when preparing the hard carbon coating layer using chemical vapor deposition, a mixture of acetylene and carrier gas is continuously introduced into the reaction system. The flow rate of the acetylene-carrier gas is 50~300 sccm, the volume ratio of acetylene to carrier gas in the mixture is 1:(2~10), the deposition temperature is 400~550℃, and the deposition time is 1~4h.

[0065] Research has shown that acetylene can undergo stable thermal decomposition at 400–550 °C, uniformly depositing a dense and complete hard carbon coating layer on the surface of the mesophase material. This temperature range is lower than the initial reaction temperature for silicon-acetylene reaction to form silicon carbide, thus avoiding the formation of additional silicon carbide impurities and achieving only a pure hard carbon coating. Simultaneously, the mild deposition temperature does not damage the inherent structure of the internal silicon nanowires and amorphous silicon carbide. Combined with a reasonable mixed gas flow rate and ratio, the thickness and density of the hard carbon layer can be precisely controlled. This not only prevents the electrolyte from directly eroding the internal silicon-based components and stabilizes the electrode interface and SEI film structure, but also improves the overall conductivity and structural integrity of the material, effectively buffering silicon charge-discharge volume deformation, reducing irreversible capacity loss, and enhancing initial coulombic efficiency and long-term cycling stability.

[0066] In practical applications, in steps 2 to 5, the carrier gas is any one or both of nitrogen and argon. In the specific embodiments of the present invention, argon is used as the carrier gas.

[0067] Thirdly, the present invention provides a battery comprising the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0068] To make the technical problems, technical solutions and technical advantages of the present invention clearer, a detailed description will be given below with reference to specific examples. However, the scope of protection of the present invention is not limited to the following specific embodiments.

[0069] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0070] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0071] Example 1: A method for preparing a silicon-carbon composite material includes the following steps: The porous carbon matrix used is phenolic resin-based porous carbon spheres with a pore volume of approximately 0.8 cm³. 3 / g, with a particle size D50 of 5μm.

[0072] Step 1: Place the porous carbon matrix in an ozone reactor and introduce a mixture of ozone and oxygen (ozone volume concentration of 5%) at a flow rate of 50 sccm. Treat at room temperature for 30 min to introduce oxygen-containing functional groups onto the surface of the porous carbon matrix.

[0073] Step 2: The porous carbon matrix containing oxygen-containing functional groups introduced in Step 1 is placed in a fluidized bed CVD reactor and heated to 550°C under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:4 and a flow rate of 100 sccm. The silane partial pressure within the reactor is controlled at 2 kPa. Silane undergoes pyrolysis to precipitate silicon, which preferentially deposits within the pores of the porous carbon matrix over a period of 4 hours. Step 2 controls the silicon deposition to account for 80 wt% of the target total silicon content, yielding the first intermediate particles.

[0074] Step 3: First, Au nanoparticles are loaded onto the surface of the first intermediate particle using radio frequency plasma sputtering. The target material is a high-purity Au target (purity ≥99.99%), the sputtering power is 100W, the sputtering time is 60s, and the sputtering temperature is room temperature. Then, a silane-argon mixture is continuously introduced to grow silicon nanowires. The volume ratio of silane to argon is 1:4, the partial pressure of silane in the reaction system is 2kPa, the deposition temperature is 550℃, and the deposition time is 30min. Silicon nanowires are grown on the surface of the first intermediate particle, thus obtaining the second intermediate particle. The resulting nanowires have an average diameter of 50nm, an average length of 1200nm, an aspect ratio L / D = 24, and a coverage Sn / Sc = 0.72. This step controls the silicon deposition amount to 20wt% of the target total silicon content.

[0075] Step 4: Place the second intermediate particle in a fluidized bed CVD reactor, introduce an acetylene-argon mixture at a flow rate of 100 sccm, and ensure the volume ratio of acetylene to argon in the mixture is 1:3. Heat the mixture to 700℃ for 15 min to deposit an amorphous silicon carbide layer on the surface of the second intermediate particle, thus obtaining the intermediate phase material.

[0076] Step 5: A hard carbon layer is deposited on the surface of the mesophase material by chemical vapor deposition. The mesophase material is placed in a reactor and an acetylene-argon mixture is continuously introduced. The volume ratio of acetylene to argon in the mixture is 1:5. The deposition temperature is 550℃ and the deposition time is 2h, thus obtaining the silicon-carbon composite material. The total silicon content in the silicon-carbon composite material is determined to be 48wt% by TGA (thermogravimetric analysis).

[0077] Figure 2 The images show cross-sectional electron microscopy images of the silicon-carbon composite material prepared in Example 1. As can be seen from the two images, the obtained silicon-carbon composite material has a regular spherical particle morphology with uniform particle size. The particle size matches the initial porous carbon matrix (about 5 μm). There is no obvious agglomeration or breakage. The particle surface is smooth and completely coated, indicating that the multi-level coating structure has been successfully constructed, providing a good structural basis for the subsequent electrochemical performance.

[0078] Figure 3 and Figure 4All images are surface electron microscopy (SEM) images of the mesophase material obtained in Example 1, from... Figures 3-4 It can be seen that silicon nanowires are interwoven in a relatively sparse form on the particle surface, with obvious open pores between the wires. The surface layer of silicon nanowires still maintains its nanowire morphology after carbonization treatment. The silicon nanowire array is not excessively densely packed, which leaves sufficient buffer space for the volume expansion of silicon. At the same time, the open pores are conducive to electrolyte penetration and rapid lithium ion transport.

[0079] Example 2: A method for preparing a silicon-carbon composite material differs from Example 1 in that the silicon content in the silicon-carbon composite material is increased to about 52 wt%, and the amount of silicon filling in the pores is increased by extending the silicon deposition time in steps 2 and 3.

[0080] The porous carbon matrix used is the same as in Example 1.

[0081] Step 1 is the same as in Example 1.

[0082] The specific operation and deposition parameters for step 2 are the same as those for step 2 in Example 1, except that the silicon deposition time is extended to 5.5 hours. This step controls the silicon deposition amount to account for 82% of the target total silicon content.

[0083] The specific operations and deposition parameters in step 3 are the same as in step 3 of Example 1, except that the silicon growth time is extended to 40 min. The resulting nanowires have an average diameter of 38 nm, an average length of 900 nm, an aspect ratio of L / D = 24, and a coverage of Sn / Sc = 0.72. This step controls the silicon deposition amount to 18% of the target total silicon content.

[0084] Steps 4 and 5 are the same as in Example 1.

[0085] Example 3: A method for preparing a silicon-carbon composite material differs from Example 1 in that it uses a smaller particle size porous carbon matrix, reduces the surface nanowire coverage, and increases the proportion of silicon mass within the pores.

[0086] The porous carbon matrix used was prepared by using phenolic resin as the carbon source precursor, and then carbonizing and activating it. The porous carbon matrix had a D50 particle size of 3 μm and a pore volume of approximately 0.7 cm³. 3 / g.

[0087] Step 1 is the same as in Example 1.

[0088] Step 2: The porous carbon matrix containing oxygen-containing functional groups introduced in Step 1 is placed in a fluidized bed CVD reactor and heated to 460℃ under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:4. The silane partial pressure in the reactor is controlled at 1.2 kPa, and the deposition time is 3.5 h. Step 2 controls the silicon deposition amount to 85 wt% of the target total silicon content, obtaining the first intermediate particles.

[0089] Step 3: First, Au nanoparticles are loaded onto the surface of the first intermediate particle using radio frequency plasma-assisted deposition. The target material is a high-purity Au target (purity ≥99.99%), the sputtering power is 80W, and the sputtering time is 60s. Then, a silane-argon mixture is continuously introduced for silicon nanowire growth. The volume ratio of silane to argon is 1:4, the silane partial pressure is 3kPa, the deposition temperature is 520℃, and the deposition time is 25min. Silicon nanowires are grown on the surface of the first intermediate particle, thus obtaining the second intermediate particle. The resulting nanowires have an average diameter of approximately 50nm, an average length of 750nm, an aspect ratio L / D = 15, and a coverage Sn / Sc = 0.48. This step controls the silicon deposition amount to 15wt% of the target total silicon content.

[0090] Steps 4 and 5 are the same as in Example 1.

[0091] Example 4: A method for preparing a silicon-carbon composite material differs from Example 1 in that: step 4, the carbonization heat treatment process, is adjusted to form a thicker amorphous silicon carbide intermediate interface layer.

[0092] Steps 1 through 3 are the same as in the example.

[0093] Step 4: Place the second intermediate particle in a fluidized bed CVD reactor, introduce an acetylene-argon mixture at a flow rate of 100 sccm, and maintain a volume ratio of acetylene to argon of 1:3. Heat the mixture to 750℃ for 25 min to deposit an amorphous silicon carbide layer on the surface of the second intermediate particle, thus obtaining the intermediate phase material.

[0094] Step 5 is the same as in Example 1.

[0095] Example 5: A method for preparing a silicon-carbon composite material differs from Example 1 in that the type of nano-metal catalyst in step 3 is adjusted, and Sn nanoparticles are used instead of Au as the catalyst.

[0096] The porous carbon matrix used is the same as in Example 1.

[0097] The preparation method is as follows: Steps 1 to 2 are the same as in Example 1.

[0098] Step 3: First, Sn nanoparticles are loaded onto the surface of the first intermediate particle using a SnCl2 impregnation-thermal reduction method. The first intermediate particle is impregnated in a 0.05 mol / L SnCl2 ethanol solution, stirred for 30 min, filtered, and vacuum dried at 60 °C for 4 h. Then, it is heat-treated at 400 °C for 2 h in an H2-Ar mixed atmosphere (H2 volume fraction 5%) to reduce SnCl2 to Sn nanoparticles. Next, a silane-argon mixed gas is continuously introduced for silicon nanowire growth. The volume ratio of silane to argon is 1:4, the silane partial pressure is 4 kPa, the deposition temperature is 530 °C, and the deposition time is 30 min. Silicon nanowires are grown on the surface of the first intermediate particle, thus obtaining the second intermediate particle. The obtained nanowires have an average diameter of 45 nm, an average length of 900 nm, an aspect ratio L / D = 20, and a coverage Sn / Sc = 0.65. This step controls the silicon deposition amount to 20 wt% of the target total silicon content.

[0099] Steps 4 and 5 are the same as in Example 1.

[0100] Example 6: A method for preparing a silicon-carbon composite material differs from Example 1 in that: in step 3, no external metal catalyst is added, and oxygen-assisted PECVD is used to deposit silicon nanowires.

[0101] The porous carbon matrix used is the same as in Example 1.

[0102] The preparation method is as follows: Steps 1 to 2 are the same as in Example 1.

[0103] Step 3: Without adding an external catalyst, the first intermediate particle is placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus. The oxygen concentration in the reaction chamber is controlled at 0.1–0.5 vol%, the RF plasma power supply is 250 W, the deposition temperature in the reaction chamber is 580 °C, the partial pressure of silane in the reaction chamber is 8 kPa, and the deposition time is 45 min. The resulting nanowires have a diameter of 55 nm, a length of approximately 1.1 μm, an L / D ratio of 20, and a coverage ratio of Sn / Sc of 0.55. Step 3 controls the silicon deposition amount to be 20 wt% of the target total silicon content.

[0104] Steps 4 and 5 are the same as in Example 1.

[0105] Example 7: A method for preparing a silicon-carbon composite material includes the following steps: The porous carbon matrix used is phenolic resin-based porous carbon spheres with a pore volume of approximately 0.5 cm³. 3 / g, with a particle size D50 of 2μm.

[0106] Step 1: Place the porous carbon matrix in an ozone reactor and introduce a mixture of ozone and oxygen (ozone volume concentration of 3%) at a flow rate of 30 sccm. Treat at room temperature for 20 min to introduce oxygen-containing functional groups onto the surface of the porous carbon matrix.

[0107] Step 2: The porous carbon matrix containing oxygen-containing functional groups introduced in Step 1 is placed in a fluidized bed CVD reactor and heated to 450°C under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:2. The silane partial pressure in the reactor is controlled at 1 kPa, and the deposition time is 2 hours. Step 2 controls the silicon deposition amount to be 50 wt% of the target total silicon content, obtaining the first intermediate particles.

[0108] Step 3: First, Au nanoparticles are loaded onto the surface of the first intermediate particle using radio frequency plasma-assisted deposition. A high-purity Au target (purity ≥99.99%) is used as the target material, with a sputtering power of 50W and a sputtering time of 30s. Then, a silane-argon mixture is continuously introduced for silicon nanowire growth. The volume ratio of silane to argon is 1:2, the silane partial pressure is 1 kPa, the deposition temperature is 400℃, and the deposition time is 15 min. Silicon nanowires are grown on the surface of the first intermediate particle, resulting in the second intermediate particle. The obtained nanowires have an average diameter of 10 nm, an average length of 240 nm, an aspect ratio L / D = 24, and a coverage Sn / Sc = 0.3. This step controls the silicon deposition amount to 50 wt% of the target total silicon content.

[0109] Step 4: Place the second intermediate particle in a fluidized bed CVD reactor, introduce an acetylene-argon mixture at a flow rate of 50 sccm, and maintain a volume ratio of acetylene to argon of 1:2. Heat the mixture to 650℃ for 10 min to deposit an amorphous silicon carbide layer on the surface of the second intermediate particle, thus obtaining the intermediate phase material.

[0110] Step 5: A hard carbon layer is coated onto the surface of the mesophase material by chemical vapor deposition. The mesophase material is placed in a reactor and an acetylene-argon mixture is continuously introduced. The ratio of acetylene to argon in the mixture is 1:2. The deposition temperature is 500°C and the deposition time is 1 hour to obtain the silicon-carbon composite material. The silicon content in the silicon-carbon composite material is 40 wt%.

[0111] Example 8: A method for preparing a silicon-carbon composite material includes the following steps: The porous carbon matrix used is phenolic resin-based porous carbon spheres with a pore volume of approximately 0.8 cm³. 3 / g, with a particle size D50 of 5μm.

[0112] Step 1: Place the porous carbon matrix in an ozone reactor, introduce a mixture of ozone and oxygen (ozone volume concentration of 8%) at a flow rate of 80 sccm, and treat at 40°C for 15 min to introduce oxygen-containing functional groups onto the surface of the porous carbon matrix.

[0113] Step 2: The porous carbon matrix containing oxygen-containing functional groups introduced in Step 1 is placed in a fluidized bed CVD reactor and heated to 550°C under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:4, and the silane partial pressure within the reactor is controlled at 2 kPa. Silane undergoes pyrolysis to precipitate silicon, which preferentially deposits within the pores of the porous carbon matrix over a period of 4 hours. Step 2 controls the silicon deposition to account for 82 wt% of the target total silicon content, yielding the first intermediate particles.

[0114] Step 3: First, Au nanoparticles were loaded onto the surface of the first intermediate particle using radio frequency plasma-assisted deposition. A high-purity Au target (purity ≥99.99%) was used as the target material, with a sputtering power of 150W, a sputtering time of 120s, and a substrate temperature of 200℃. Then, a silane-argon mixture was continuously introduced for silicon nanowire growth. The volume ratio of silane to argon in the mixture was 1:10. The partial pressure of silane in the reaction system was controlled at 5kPa, the deposition temperature was 550℃, and the deposition time was 50min. Silicon nanowires were grown on the surface of the first intermediate particle, resulting in the second intermediate particle. The obtained nanowires had an average diameter of 100nm, an average length of 2400nm, an aspect ratio of L / D = 24, and a coverage of Sn / Sc = 0.72. This step controlled the silicon deposition amount to 18wt% of the target total silicon content.

[0115] Step 4: Place the second intermediate particle in a fluidized bed CVD reactor, introduce an acetylene-argon mixture with a flow rate of 200 sccm, and a volume ratio of acetylene to argon of 1:3. Heat the mixture to 700℃ for 15 min to deposit an amorphous silicon carbide layer on the surface of the second intermediate particle, thus obtaining the intermediate phase material.

[0116] Step 5: A hard carbon layer is deposited onto the surface of the mesophase material via chemical vapor deposition. The mesophase material is placed in a reactor, and an acetylene-argon mixture is continuously introduced. The volume ratio of acetylene to argon in the mixture is 1:5. The deposition temperature is 450℃, and the deposition time is 2 hours, thus obtaining the silicon-carbon composite material. The silicon content in the silicon-carbon composite material is 60 wt%. Comparative Example 1: This comparative example provides a silicon-carbon composite material that differs from Example 1 in that it has no surface functionalization, no gradient structure, and no nanowire array.

[0117] The porous carbon matrix used is the same as in Example 1.

[0118] The preparation method is as follows: Step 1: The porous carbon matrix is ​​placed in a fluidized bed CVD reactor and heated to 550°C under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:4 and a silane partial pressure controlled at 2 kPa. Silane undergoes pyrolysis to precipitate silicon, which preferentially deposits within the pores of the porous carbon matrix over a period of 5.5 h.

[0119] Step 2: Place the above-mentioned silicon-containing porous carbon in a fluidized bed CVD reactor, introduce acetylene-argon gas with a volume ratio of 1:3 and a total flow rate of 100 sccm, heat to 700℃ for 15 min, deposit an amorphous silicon carbide layer on the particle surface with a thickness of about 5 nm, and obtain silicon carbide-coated silicon-containing porous carbon.

[0120] Step 3: A hard carbon layer is coated by chemical vapor deposition, with a continuous flow of an acetylene-argon mixture (volume ratio of acetylene to argon of 1:5), a deposition temperature of 550°C, and a deposition time of 2 hours, thus obtaining the silicon-carbon composite material. Comparative Example 2: This comparative example provides a silicon-carbon composite material, which differs from Example 1 in that step S4 is omitted and an amorphous silicon carbide layer is not provided.

[0121] The porous carbon matrix used is the same as in Example 1.

[0122] The preparation method is as follows: Steps 1 to 3 are the same as in Example 1.

[0123] Step 4 is omitted.

[0124] Step 5 is the same as in Example 1.

[0125] Comparative Example 3: This comparative example provides a silicon-carbon composite material, which differs from Example 1 in that: no hard carbon layer is provided, and step S5 is omitted.

[0126] The porous carbon matrix used is the same as in Example 1.

[0127] The preparation method is as follows: Steps 1 to 4 are the same as in Example 1.

[0128] Step 5 is omitted.

[0129] Comparative Example 4: This comparative example provides a silicon-carbon composite material, which differs from Example 1 in that the porous carbon matrix is ​​not surface-functionalized, and step 1 is omitted.

[0130] The porous carbon matrix used is the same as in Example 1.

[0131] The preparation method is as follows: Step 1 is omitted.

[0132] Steps 2 through 5 are the same as in Example 1.

[0133] Comparative Example 5: This comparative example provides a silicon-carbon composite material, which differs from Example 1 in that: nano-silicon is not deposited on the surface of the first intermediate particle, and step 3 is omitted.

[0134] The porous carbon matrix used is the same as in Example 1.

[0135] The preparation method is as follows: Step 1 is the same as in Example 1.

[0136] Step 2: The porous carbon matrix is ​​placed in a fluidized bed CVD reactor and heated to 550°C under an Ar atmosphere. A silane-argon mixture is introduced, with a silane to argon volume ratio of 1:4 and a silane partial pressure controlled at 2 kPa. Silane is pyrolyzed to precipitate silicon, which preferentially deposits inside the pores of the porous carbon matrix over a period of 5.5 h.

[0137] Step 3 is omitted.

[0138] Steps 4 and 5 are the same as in Example 1.

[0139] The silicon-carbon composite materials obtained in the examples and comparative examples were tested using the following testing methods.

[0140] Silicon content: determined by gravimetric method. Weigh about 1g of sample and ignite it in air at 1000℃ to constant weight. Calculate the carbon content from the mass difference before and after ignition, and the remainder is the silicon content.

[0141] Radial silicon content gradient: Cross-sections of silicon-carbon composite particles were prepared using argon ion polishing. The cross-sectional morphology of the particles was observed by SEM and combined with EDS line scan analysis. The proportions of silicon mass contributed by silicon particles to the total silicon mass of the particles (M1) and silicon mass contributed by silicon nanoparticles to the total silicon mass of the particles (M2) were calculated. The radial silicon content gradient was calculated as M1 / M2. The radial silicon content gradient was used to quantify the radial silicon content gradient. The larger the ratio, the more preferentially silicon is enriched in the porous regions inside the particles.

[0142] Aspect ratio of silicon nanowires: The average diameter D and average length L of silicon nanowires on the surface of the second intermediate particle were measured by SEM image analysis, and the aspect ratio L / D was calculated.

[0143] Coverage: The number of silicon nanowires per unit area was counted by analyzing SEM images to obtain the number density, and the coverage Sn / Sc of the silicon nanowire array was calculated by combining it with the total external surface area of ​​the carbon matrix.

[0144] Powder resistance: The four-probe method was used for measurement. Approximately 1g of powder was placed into a mold and pressed into a disc under a pressure of 10MPa. The resistance value was measured using a four-probe resistivity tester, and the resistivity (Ω·cm) was calculated.

[0145] Specific surface area: determined by nitrogen adsorption method (BET method). Approximately 0.5–1 g of sample was degassed under vacuum at 300 °C for 3 h. High-purity nitrogen was used as the adsorbate, and adsorption-desorption isotherms were measured at liquid nitrogen temperature (77 K). The specific surface area (m²) was calculated using the BET equation. 2 / g).

[0146] Using nitrogen adsorption, let the volume of silicon particles be V1 and the total pore volume of the porous carbon matrix be V2. Take the porous carbon matrix after surface functionalization in step 1 and measure its total pore volume V2 (cm). 3 / g); Take the first intermediate particle obtained in step 2 and determine its residual pore volume V3 (cm). 3 / g); the pore volume occupied by silicon particles V1=V2 V3 can be obtained by calculating the ratio of V1 to V2.

[0147] Table 1. Performance characterization of silicon-carbon composite materials prepared in Examples 1-8 and Comparative Examples 1-5 Examples 1-6 all exhibit excellent structure and physical properties adapted to the "multi-level gradient confinement network": First, the radial silicon content gradient is reasonable (4.0-5.7), reflecting the gradient distribution characteristics of silicon particles within the pores and silicon nanowires on the surface, laying the foundation for "first-level chemical anchoring confinement within the pores"; second, the aspect ratio (15-24) and coverage (0.48-0.72) of the silicon nanowires match the structural requirements of "second-level one-dimensional flexible release buffer," balancing flexible deformation capability and structural stability; third, the powder resistivity is low (20-30 Ω·cm), thanks to the continuous conductive network constructed by the porous carbon matrix, silicon nanowire array, silicon carbide layer, and hard carbon layer, effectively reducing interfacial contact impedance and ensuring rapid charge transport. The synergistic optimization of the above structure and physical properties is the core prerequisite for the material to achieve subsequent excellent electrochemical performance.

[0148] Comparing Example 1 and Comparative Example 1, Comparative Example 1, without silicon nanowire structure, exhibits a powder resistivity as high as 45 Ω·cm. Example 1 achieves silicon enrichment and gradient distribution within the pores through Si-OC chemical bonding, and, in conjunction with a silicon nanowire array, constructs a continuous conductive pathway, reducing the resistivity to 25 Ω·cm. This demonstrates that the radial silicon content gradient and one-dimensional nanowire structure are key to reducing material resistance and optimizing structural order.

[0149] Comparing Example 1 and Comparative Example 2, Comparative Example 2, which lacks an amorphous silicon carbide layer, has a similar radial gradient and nanowire parameters to Example 1, but its powder resistivity increases to 42 Ω·cm. Example 1, due to the strong transition effect of the silicon carbide interlayer, enhances the interlayer bonding and electronic conduction, resulting in a significantly lower resistivity, demonstrating the reinforcing effect of the silicon carbide layer on the integrity of the conductive network.

[0150] Comparing Example 1 and Comparative Example 3, Comparative Example 3, without an outer hard carbon coating, had a powder resistivity of 38 Ω·cm, higher than the 25 Ω·cm of Example 1. This indicates that the hard carbon outer layer not only provides mechanical constraint but also further improves the conductive network, enhancing the overall conductivity of the material. This verifies the positive contribution of the fourth-order outer mechanical constraint to the physical properties.

[0151] Comparing Example 1 and Comparative Example 4, Comparative Example 4 did not perform surface functionalization on the porous carbon matrix, resulting in a lack of Si-OC chemical bonding between silicon particles and carbon pore walls. The radial silicon content gradient decreased slightly to 3.5, and the powder resistivity increased to 32 Ω·cm. Example 1, through ozone oxidation treatment, introduced oxygen-containing functional groups, achieving chemical anchoring of silicon particles within the pores, enhancing the carbon-silicon interfacial bonding, and reducing interfacial contact impedance. This demonstrates the necessity of surface functionalization for constructing a stable conductive network and strengthening interfacial bonding.

[0152] Comparing Example 1 and Comparative Example 5, Comparative Example 5 did not grow a silicon nanowire array and lacked an external one-dimensional flexible buffer layer; all silicon was concentrated inside the channels, resulting in a powder resistivity of 35 Ω·cm, higher than the 25 Ω·cm of Example 1. Example 1, through the construction of continuous conductive channels and provision of flexible expansion space on the particle surface using a silicon nanowire array, significantly reduced the powder resistivity, verifying the crucial role of the silicon nanowire array in constructing a complete conductive network and optimizing the radial gradient distribution.

[0153] Electrode and half-cell preparation and electrochemical performance testing: The silicon-carbon composite materials prepared in Examples 1-8 and Comparative Examples 1-5 were used as negative electrode active materials to prepare negative electrode sheets. The electrode sheet composition was as follows: 90 wt% active material, 5 wt% SBR binder, 4.9 wt% conductive agent SP, and 0.1 wt% SWCNT. CR2032 coin cells were prepared using conventional methods for the negative electrode sheets, and the electrical performance of the cells was tested. The specific test methods were as follows: (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC∶DEC=1∶1), wherein the concentration of LiPF6 is 1mol / L. The battery was charged and discharged using the LAND battery testing system. (2) Capacity test: After the CR2032 button battery is left to stand for 6 hours, it is discharged at 0.1C to 0.005V, and then discharged at a constant voltage of 0.005V until the current is cut off at 0.01C. After standing for 5 minutes, it is charged at a constant current of 0.1C to 1.5V and the capacity is recorded. (3) Capacity retention rate test: After standing for 5 minutes, repeat the above charge and discharge steps twice; then discharge to 0.005V at 0.5C; after standing for 5 minutes, charge to 1.5V at 0.5C constant current, cycle 300 times; calculate the capacity retention rate by the charge specific capacity of the 300th cycle / the charge capacity of the 1st cycle × 100%. (4) Electrode expansion rate: After the CR2032 type button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C and then discharged to 0.005V at 0.01C. Then the button cell was disassembled in the glove box, the electrode was cleaned with DMC and the thickness of the electrode was measured. The expansion rate was calculated as: (thickness of electrode in the first fully charged state - thickness of fresh electrode) / thickness of fresh electrode × 100%. The test results are shown in Table 1.

[0154] Table 2 Electrochemical performance of batteries made from silicon-carbon composite materials prepared in Examples 1-8 and Comparative Examples 1-5 The electrochemical performance of Examples 1-8 is comprehensively superior to that of the comparative examples, demonstrating synergistic advantages of "high capacity, high first-efficiency, long cycling, and low expansion": the first-efficiency coulombic efficiency reaches 88.2%~91.0%, the specific capacity retention rate is as high as 88.5%~94.8%, and the electrode expansion rate is only 18%~32%. This excellent performance is due to the multi-level gradient confinement mechanism of "chemical anchoring, flexible release, strong and tough transition, and hard carbon confinement". Si-OC bonding and pore confinement inhibit silicon shedding and excessive expansion, the flexible release of stress by silicon nanowires avoids structural pulverization, and the silicon carbide layer and hard carbon layer synergistically block the electrolyte and stabilize the SEI film, ultimately achieving comprehensive optimization of electrochemical performance.

[0155] Comparing Examples 1 and 6, Example 1 showed better initial coulombic efficiency, 300-cycle capacity retention, and electrode expansion rate than Example 6. This indicates that the process of growing silicon nanowires using Au nanoparticles in Example 1, compared to the oxygen-assisted PECVD process without metal catalysts in Example 6, resulted in a silicon-carbon composite material with better structural stability. This process effectively improved the initial coulombic efficiency, delayed cycle capacity decay, and better suppressed electrode volume expansion, demonstrating the advantages of metal catalysis in constructing ordered silicon nanowire structures, optimizing stress buffering, and stabilizing the electrode interface.

[0156] Furthermore, the sample data from Example 7 demonstrates superior electrochemical performance. In Example 7, the silicon particle volume accounts for only 30% of the total pore volume of the porous carbon (V1 / V2=0.30), leaving ample expansion buffer space within the pores. Most of the lithium intercalation expansion is absorbed by the pore channels, significantly reducing the stress transmitted to the outer layer. Simultaneously, the total silicon content is 40wt%, resulting in a small absolute volume change. Under these conditions, the silicon nanowire array, with a sparse but still preferred surface, is sufficient to work in conjunction with the hard carbon layer to dissipate and ultimately confine residual stress, thereby achieving extremely low expansion and excellent cycling stability.

[0157] Comparing Example 1 and Comparative Example 1, Comparative Example 1, lacking a gradient structure, Si-OC bonding, and nanowire array, exhibits an initial coulombic efficiency of only 84.5%, a specific capacity retention of 74.5%, and an electrode expansion rate as high as 58%. Example 1, with its multi-level gradient structure, achieves a 5 percentage point improvement in initial efficiency, a 17 percentage point improvement in cycle retention, and a 33 percentage point reduction in expansion rate, demonstrating that gradient and integrated structures are the core technological path to solving the problems of poor cycle performance and large expansion in silicon-based materials.

[0158] Comparing Example 1 and Comparative Example 2, Comparative Example 2, lacking an amorphous silicon carbide layer, exhibited a first-efficiency coulombic efficiency of 87.0%, a specific capacity retention of 82.5%, and an electrode expansion rate of 38%, all inferior to Example 1 (89.5%, 91.5%, and 25%, respectively). This difference indicates that the silicon carbide interlayer effectively suppresses interfacial delamination and repeated SEI film regeneration, significantly improving interfacial stability, thereby enhancing first-efficiency and cycle performance and reducing expansion.

[0159] Comparing Example 1 and Comparative Example 3, Comparative Example 3, lacking an outer hard carbon coating, achieved an initial coulombic efficiency of only 82.0%, a specific capacity retention of 70.5%, and an electrode expansion rate of 52%. Example 1, due to the dense barrier and mechanical constraint of the hard carbon layer, achieved a 7.5% improvement in initial efficiency, a 21% improvement in cycle retention, and a 27% reduction in expansion rate, highlighting the indispensability of the hard carbon outer layer in stabilizing the electrode interface and inhibiting electrolyte erosion.

[0160] Comparing Example 1 and Comparative Example 4, Comparative Example 4 did not perform surface functionalization on the porous carbon matrix, resulting in the absence of Si-OC chemical bonding. Its initial coulombic efficiency (86.5%), specific capacity retention (85.0%), and electrode expansion rate (32%) were all inferior to Example 1 (89.5%, 91.5%, and 25%, respectively). Example 1 introduced oxygen-containing functional groups through ozone oxidation treatment, achieving chemical anchoring of silicon particles within the pores, enhancing the carbon-silicon interface bonding, improving initial efficiency by 3%, cycle retention by 6.5%, and reducing expansion rate by 7%, demonstrating the crucial role of surface functionalization and chemical bonding in interface stability and structural integrity.

[0161] Comparing Example 1 and Comparative Example 5, Comparative Example 5, lacking a silicon nanowire array and an external one-dimensional flexible buffer layer, exhibited significantly lower initial coulombic efficiency (86.0%), specific capacity retention (78.5%), and electrode expansion rate (45%) compared to Example 1 (89.5%, 91.5%, and 25%, respectively). Example 1, through the bending, torsion, and gap-accommodating capabilities of the silicon nanowire array, flexibly released expansion stress, resulting in a 3.5% improvement in initial efficiency, a 13% improvement in cycle retention, and a 20% reduction in expansion rate. This verifies the irreplaceable role of the silicon nanowire array as a second-level flexible buffer layer in suppressing volume expansion and improving cycle stability.

[0162] The above-described embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope of the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, It includes a porous carbon matrix, silicon particles, silicon nanowires, and a hard carbon layer; The silicon particles are distributed within the pores of the porous carbon matrix; and the silicon particles are bonded to the porous carbon matrix through Si-OC chemical bonds, and the particles formed by the silicon particles and the porous carbon matrix are the first intermediate particles. The silicon nanowires at least cover a portion of the surface of the first intermediate particle; the particle formed by the first intermediate particle and the silicon nanowires is the second intermediate particle; The silicon nanowires are carburized to form an amorphous silicon carbide layer. The specific process is as follows: the second intermediate particles are treated by chemical vapor deposition, and an acetylene-carrier gas mixture is introduced. The silicon nanowires are transformed in situ through the carburizing reaction to form an amorphous silicon carbide layer, thus obtaining the intermediate phase material. The carburizing temperature is 650~800℃ and the carburizing time is 10~30min. The hard carbon layer covers at least part of the surface of the mesophase material; the specific process is as follows: a hard carbon layer is deposited on the surface of the mesophase material by chemical vapor deposition, an acetylene-carrier gas mixture is introduced, and a hard carbon layer is deposited on the surface of the mesophase material at a deposition temperature of 400~550℃ and a deposition time of 1~4h; thus, the silicon-carbon composite material is obtained.

2. The silicon-carbon composite material as described in claim 1, characterized in that, The total mass content of silicon in the silicon-carbon composite material is 40wt%~60wt%; The specific surface area of ​​the silicon-carbon composite material is 0.5~8m². 2 / g; The resistivity of the silicon-carbon composite material powder is 10~80 Ω·cm.

3. The silicon-carbon composite material as described in claim 1 or 2, characterized in that, The ratio of the volume of the silicon particles to the total pore volume of the porous carbon matrix is ​​0.3 to 0.

7. The porous carbon matrix has a D50 of 2–8 μm and a pore volume of 0.5–1.0 cm³. 3 / g; The silicon nanowires have an average length of L and an average width of D, where 10 ≤ L / D ≤ ​​200. The silicon nanowire coating area is Sn, and the surface area of ​​the first intermediate particle is Sc, where 0.3 ≤ Sn / Sc ≤ 0.9; The ratio of the mass of silicon in the first intermediate particle to the mass of silicon in the second intermediate particle is (0.7~0.9):

1.

4. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: Step 1, Surface functionalization: The porous carbon matrix is ​​subjected to ozone oxidation treatment; specifically, the porous carbon matrix is ​​placed in an ozone reactor, and a mixture of ozone and oxygen is introduced to introduce oxygen-containing functional groups on the surface of the porous carbon matrix. Step 2, silicon deposition: The product from Step 1 is subjected to vapor phase deposition by introducing a mixture of silane and carrier gas to deposit silicon, thereby obtaining the first intermediate particles. Step 3, silicon nanowire growth: Silicon nanowires are grown on the surface of the first intermediate particle by introducing a silane-carrier gas mixture through chemical vapor deposition to obtain the second intermediate particle; The silicon nanowire growth process is as follows: nano-metal catalytic particles are deposited on the surface of the first intermediate particle as a catalyst, and then silicon nanowires are grown by introducing a silane-carrier gas mixture through chemical vapor deposition. Alternatively, oxygen-assisted plasma-enhanced chemical vapor deposition can be used to deposit silicon nanowires. Step 4, carburizing to form an amorphous silicon carbide layer: The second intermediate particles are treated by chemical vapor deposition, and an acetylene-carrier gas mixture is introduced. The silicon nanowires are transformed in situ through the carburizing reaction to form an amorphous silicon carbide layer, thus obtaining the intermediate phase material; the carburizing temperature is 650~800℃, and the carburizing time is 10~30min. Step 5, Deposit hard carbon layer: Deposit hard carbon layer on the surface of mesophase material by chemical vapor deposition process, introduce acetylene-carrier gas mixture to deposit hard carbon layer on the surface of mesophase material, the deposition temperature is 400~550℃, the deposition time is 1~4h; thus, the silicon-carbon composite material is obtained.

5. The method for preparing the silicon-carbon composite material as described in claim 4, characterized in that, In step 1, the porous carbon matrix has a D50 of 2~8 μm and a pore volume of 0.5~1.0 cm³. 3 / g; The surface functionalization process is as follows: a porous carbon matrix is ​​placed in an ozone reactor, a mixture of ozone and oxygen is introduced, the ozone volume concentration is controlled at 1% to 10%, the gas flow rate is 20 to 100 sccm, the reaction temperature is 15 to 60℃, and the reaction time is 10 to 40 min, thereby introducing oxygen-containing functional groups on the surface of the porous carbon matrix.

6. The method for preparing the silicon-carbon composite material as described in claim 4 or 5, characterized in that, In step 2, the volume ratio of silane to carrier gas in the reaction system is 1:(2~10), the partial pressure of silane in the reaction system is 1~5kPa, the deposition temperature is 450~600℃, and the deposition time is 2~6h.

7. The method for preparing the silicon-carbon composite material as described in claim 4, characterized in that, In step 4, the flow rate of the acetylene-carrier gas mixture is 50~200 sccm, and the volume ratio of acetylene to carrier gas in the mixture is 1:(2~5).

8. The method for preparing the silicon-carbon composite material as described in claim 4 or 5, characterized in that, In step 5, the flow rate of the acetylene-carrier gas mixture is 50~300 sccm, and the volume ratio of acetylene to carrier gas in the mixture is 1:(2~10).

9. A battery, characterized in that, The silicon-carbon composite material includes the silicon-carbon composite material according to any one of claims 1 to 3 or the silicon-carbon composite material prepared by any one of claims 4 to 8.

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