Silicon-carbon composite material and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly discloses a silicon-carbon composite material and a preparation method thereof.The preparation method comprises the following steps that porous carbon is placed in a rotary furnace and heated to 600-1000 DEG C in an inert atmosphere, and heteroatom gas is introduced for modification; then, silane mixed gas is introduced at the temperature of 450-600 DEG C to deposit nano silicon, and a silicon-carbon intermediate is obtained; and finally, mixing organic lithium, inorganic lithium, a cross-linking agent and a passivating agent, and coating the surface of the silicon-carbon intermediate with the mixture through physical vapor deposition to form a composite coating layer, thereby obtaining the silicon-carbon composite material. According to the method, the porous carbon structure is optimized through heteroatom doping, and the uniform and compact composite coating layer is combined, so that the volume expansion and side reaction of the silicon-carbon composite material in the charging and discharging process are effectively inhibited, the gas production rate is remarkably reduced, and the first coulombic efficiency, the cycling stability and the high-temperature storage performance of the material are improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon composite material and its preparation method. Background Technology

[0002] Silicon-carbon composite materials, as a high-energy-density anode material, typically consist of a porous carbon matrix, nano-silicon deposited in its pores, and a surface passivation layer. However, porous carbon itself has low compressive strength, making it prone to particle breakage due to external pressure during battery charging and discharging, which can lead to gas generation. Furthermore, its high specific surface area and abundant defects exacerbate side reactions, resulting in poor material performance during storage and at high temperatures.

[0003] To suppress gas production and improve cycle stability, structural optimization is needed in two aspects: first, modifying the porous carbon core to reduce its surface defects; and second, enhancing the mechanical strength of the material through external coating to mitigate volume changes and capacity decay during charging and discharging.

[0004] Although previous studies have attempted to reduce interfacial side reactions through surface coating, such as introducing amorphous silicon into porous carbon via chemical vapor deposition followed by passivation agents and gradient thermal treatment to form a passivation layer on the surface, thereby suppressing side reactions, the uniformity of the coating layer prepared by this method is still not ideal, the coating strength is limited, and the porous carbon core itself has not been modified or optimized, resulting in insufficient suppression of side reactions. Summary of the Invention

[0005] In view of this, this application provides a silicon-carbon composite material and a method for preparing the same, which solves the technical problem of poor cycle stability of silicon-carbon composite materials in the prior art.

[0006] To achieve one or more of the above objectives or other objectives, one aspect of this application provides a method for preparing a silicon-carbon composite material, specifically including the following steps: Step S1: Porous carbon is added to a rotary kiln, and after inert gas is introduced into the rotary kiln to purge air, the rotary kiln is heated to 600-1000°C, and then heteroatom gas is introduced for 30-300 minutes to obtain modified porous carbon.

[0007] Step S2: The rotary kiln temperature is maintained at 450-600℃, and a silane mixed gas is introduced. After 10-200 minutes, the temperature inside the rotary kiln is cooled to room temperature to obtain a silicon-carbon intermediate.

[0008] Step S3: Organic lithium, inorganic lithium, crosslinking agent and passivating agent are mixed evenly to obtain a coating material, and the coating material is deposited on the surface of the silicon-carbon intermediate by physical vapor deposition to obtain the silicon-carbon composite material.

[0009] In step S1, porous carbon undergoes pyrolysis and structural recombination in a high-temperature region of 600-1000℃, ensuring that heteroatom gases are fully decomposed and effectively doped into the porous carbon lattice, forming stable chemical bonds and thus optimizing the conductivity and electrochemical activity of the carbon framework. Too low a temperature (e.g., below 600℃) results in insufficient doping, while too high a temperature (e.g., above 1000℃) may lead to carbon structure collapse. By utilizing the template effect of porous carbon, the degree of heteroatom doping and the size, distribution, and loading of nano-silicon were controlled through temperature, time, and flow rate, achieving a preliminary balance between high capacity and structural stability.

[0010] In step S1, the flow rate of heteroatom gas is controlled at 1-5 L / min. Through a "slow, thorough, and uniform" reaction strategy, precise, effective, and uniform heteroatom chemical modification of porous carbon cores is achieved.

[0011] Steps S2 / S3 utilize PVD technology, employing parameters such as thickness, rate, and vacuum level, to construct a multifunctional coating layer on the surface of the silicon-carbon intermediate. This layer can both replenish lithium to improve efficiency, mechanically confine volume expansion, and chemically passivate the surface, forming a stable outer shell.

[0012] When introducing the silane mixed gas in step S2, the pressure is typically controlled at 0.1-0.15 MPa, and the flow rate at 10-50 L / min. Within the mid-temperature range of 450-600℃, silane gas chemical vapor deposition (CVD) ensures precise control over the nano-silicon deposition process (including its location, size, distribution, and morphology) by optimizing the transport behavior of the reactant gases, while maintaining safety. This ultimately yields a silicon-carbon composite anode material with stable structure and excellent electrochemical performance. Temperatures that are too low (e.g., below 450℃) result in incomplete silane decomposition, while temperatures that are too high (e.g., above 600℃) can lead to excessively large silicon particles or melting.

[0013] Preferably, the mass-to-volume ratio of the porous carbon, the heteroatom gas, and the silane mixture is 1 kg: (1-10) L: (500-2000) L.

[0014] Insufficient silane gas results in low silicon loading and underutilization of pores, leading to low energy density. Conversely, excessive silane gas clogs pores, causing silicon particles to agglomerate and grow, affecting cycle life and reducing rate performance. By precisely controlling the amount of silicon deposited, smaller and more uniformly distributed nano-silicon particles were obtained. This maximized the buffering effect of porous carbon without excessively sacrificing specific capacity, significantly improving the cycle life, structural stability, and overall electrochemical performance of silicon-carbon composites.

[0015] Insufficient heteroatom gas leads to inadequate doping, resulting in a small improvement in conductivity, uneven silicon distribution, and poor cycle performance. Excessive heteroatom gas, on the other hand, damages the porous carbon structure, causing a decrease in mechanical strength and rapid capacity decay.

[0016] The mass-to-volume ratio of the porous carbon, the heteroatom gas, and the silane mixture in this application is an optimized ratio that can simultaneously avoid the aforementioned adverse conditions.

[0017] Preferably, the mass ratio of the organic lithium, the inorganic lithium, the crosslinking agent, the passivating agent and the silicon-carbon intermediate is (5-20):(5-20):(1-5):(1-5):500.

[0018] This application combines the flexibility and high lithium replenishment capacity of organic lithium with the rigidity and high ionic conductivity of inorganic lithium to form an ideal coating structure that balances rigidity and flexibility. Too low an organic lithium content leads to insufficient pre-lithiation, resulting in an excessively thick / loose coating layer with poor toughness, resulting in insignificant initial efficiency gains, weakened buffering capacity against volume expansion, and significant capacity loss. Too high an organic lithium content increases ineffective weight, reduces energy density, increases internal resistance, and increases side reactions. Too low an inorganic lithium content results in insufficient coating strength and low ionic conductivity; too high an inorganic lithium content increases coating brittleness and weakens core bonding.

[0019] By using a small but crucial amount of crosslinking and passivating agents, the structural integrity and interfacial stability of the coating layer are significantly improved without substantially increasing its thickness and impedance. Too little crosslinking agent results in weak adhesion of the coating layer formed by physical vapor deposition, making it prone to pulverization and detachment during cycling. Too much crosslinking agent leads to a loss of flexibility, failing to effectively buffer volume changes and instead causing breakage; excessive crosslinking may also affect lithium-ion transport within the coating layer. Passivating agents maintain interfacial stability. Too little passivating agent results in an unstable interface, failing to form an effective protective layer, leading to continuous electrolyte decomposition, rapid consumption of organic / inorganic lithium, and poor cycle life. Too much passivating agent results in excessive interfacial impedance, severely hindering lithium-ion migration, increasing polarization, and a sharp decline in capacity and rate performance.

[0020] By precisely controlling the proportions of each functional component, a composite coating layer with triple functions of "lithium replenishment," "crosslinking enhancement," and "interface passivation" was constructed using PVD technology. This coating layer not only actively compensates for initial capacity loss but also passively protects the silicon-carbon core with its excellent mechanical strength and chemical stability, thereby synergistically achieving a comprehensive improvement in the initial efficiency, cycle life, and safety of silicon-carbon composite materials.

[0021] Preferably, the heteroatom gas is an organic heteroatom gas, which is formed by vaporizing at least one of pyridine, quinoline, pyrimidine, pyrrole, indole, imidazole, purine, furan, and thiophene. Alternatively, the silane mixture is formed by mixing at least one of silane, disilane, dichlorosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride with nitrogen in a volume ratio of (1-3):10.

[0022] These molecules cleave at 600-1000℃, generating active free radicals containing N, S, and O. The resulting abundant defects and active sites induce uniform nucleation and fine distribution of nano-silicon, making the structure of silicon-carbon composite materials more stable.

[0023] Silane gas is diluted with a large amount of nitrogen to control the reaction rate and achieve uniform silicon deposition while ensuring a certain silicon loading. Too little silane gas (<1 / 13, i.e., far below 1:10) will result in a slow deposition rate, low production efficiency, insufficient silicon loading, and the formation of discontinuous silicon layers, leading to a low specific capacity of the final composite material and failing to fully utilize the high capacity advantage of silicon. Too much silane gas (>3 / 13, i.e., far above 3:10) can easily lead to gas-phase nucleation and silicon particle agglomeration, severely clogging pores and forming an unstable "core-shell" structure, affecting cycle life.

[0024] Preferably, the organolithium is at least one of lithium stearate, lithium lactate, lithium acrylate, lithium citrate, and lithium acetate.

[0025] In the PVD process, organic lithium compounds can act as "binders" or "matrixes" to better mix and co-deposit with inorganic lithium, passivators and other components, which helps to form a more uniform and dense composite coating film.

[0026] Preferably, the inorganic lithium is at least one selected from lithium fluoride, lithium carbonate, lithium oxide, and lithium nitride. Alternatively, the crosslinking agent is at least one of azodicarbonamide, azobisisobutyramidine hydrochloride, diethyl azodicarbonate, azobenzenesulfonic acid, azobisisobutyronitrile, and 4-aminoazobenzene.

[0027] Inorganic lithium can enhance the mechanical strength and chemical stability of the casing, reduce ongoing side reactions during cycling, and improve cycle life.

[0028] Preferably, the passivating agent is at least one selected from CoF3, MnF3, FeF3, VF3, TiF3, NiF2, FeF2, CuF2, CuF, SnF2, and AgF.

[0029] The metal fluoride passivation layer can provide lithium nucleation sites, guide the uniform deposition of lithium ions, and greatly suppress the growth of lithium dendrites, thereby improving the battery's safety performance and fast charging capability.

[0030] Preferably, in step S3, physical vapor deposition is performed using vacuum evaporation technology, wherein the temperature is 50℃~150℃ and the vacuum degree is 2.0×10⁻⁶. -4 Pa ~ 4.0 × 10 -4 The deposition time is 30-300 minutes, and the deposition rate is 1 g / min to 10 g / min. A high-vacuum environment is used to achieve pure, uniform, dense, and contamination-free deposition while maximizing the protection of the silicon-carbon core activity and the functionality of the coating material. Too short a time (less than 30 minutes) or too slow a rate (less than 1 g / min) results in incomplete coating; too fast a rate (more than 10 g / min) results in a loose coating layer that is prone to detachment. By precisely controlling the rate and time, a composite coating layer with optimal thickness and structure is obtained, thereby synergistically improving the overall electrochemical performance of the silicon-carbon composite material.

[0031] Another aspect of this application provides a silicon-carbon composite material, which is prepared by the above-described method for preparing silicon-carbon composite materials, and has the following specific composition: A silicon-carbon composite material includes a core and a shell. The core is a composite material composed of nano-silicon and heteroatoms deposited on a porous carbon surface. The shell is an amorphous carbon and a composite material deposited on the amorphous carbon by physical vapor deposition after uniformly mixing organic lithium, inorganic lithium, crosslinking agent and passivating agent.

[0032] Preferably, the thickness of the outer shell is 100nm to 500nm.

[0033] This thickness provides sufficient mechanical support for the silicon-carbon core to buffer volume expansion and create efficient ion / electron transport channels without excessively sacrificing energy density. Too thin and the protection is insufficient; too thick and the internal resistance increases, reducing capacity.

[0034] Beneficial effects: 1. Heteroatom deposition on porous carbon cores can effectively reduce their surface activity and specific surface area, thereby reducing the occurrence of side reactions. Simultaneously, heteroatom modification helps guide the uniform deposition of nano-silicon within the porous carbon core, thereby improving the material's storage performance and suppressing gas generation.

[0035] 2. Constructing a protective layer on the surface of a silicon-carbon intermediate via physical vapor deposition (PVD) serves a dual purpose: firstly, this coating improves the integrity of the core silicon-carbon intermediate, reducing direct exposure of nano-silicon to the electrolyte and thus suppressing gas generation; secondly, the protective layer contains an artificial SEI component composed of organic and inorganic lithium, which can replenish lithium-ion losses during charging and discharging, reduce side reactions, and enhance the lithium-ion diffusion rate. Furthermore, the introduction of a crosslinking agent creates a network structure in the outer layer, enhancing the structural stability of the coating and effectively suppressing volume expansion during charging and discharging, further reducing side reactions and gas generation. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] in: Figure 1 This is a diagram illustrating a method for preparing a silicon-carbon composite material according to one embodiment. Figure 2 A schematic diagram of a silicon-carbon composite material prepared in one embodiment using scanning electron microscopy. Detailed Implementation

[0038] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0040] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0041] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0042] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same.

[0043] In this application, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "multiple" means two or more. This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0044] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way may include end values ​​or not.

[0045] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0048] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0049] Example 1 This embodiment proposes a method for preparing silicon-carbon composite materials, such as... Figure 1 As shown, the specific steps include the following: Step S1: Porous carbon modification Porous carbon is added to a rotary kiln, and after inert gas is introduced into the kiln to purge the air, the kiln is heated to 600-1000℃, and then heteroatom gas is introduced for 30-300 minutes to obtain modified porous carbon.

[0050] The heteroatom gas is an organic heteroatom gas, which is formed by vaporizing at least one of pyridine, quinoline, pyrimidine, pyrrole, indole, imidazole, purine, furan, and thiophene.

[0051] Step S2: Preparation of silicon-carbon intermediate The rotary kiln temperature is maintained at 450-600℃, and a silane mixed gas is introduced. After 10-200 minutes, the temperature inside the rotary kiln is cooled to room temperature to obtain a silicon-carbon intermediate.

[0052] The silane mixture is composed of at least one of silane, silane, dichlorosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride mixed with nitrogen, in a volume ratio of (1-3):10.

[0053] Step S3: Preparation of silicon-carbon composite material Organic lithium, inorganic lithium, crosslinking agent, and passivating agent are uniformly mixed to obtain a coating material. The coating material is then deposited on the surface of the silicon-carbon intermediate by physical vapor deposition to obtain a silicon-carbon composite material. Specifically, vacuum evaporation technology is used for physical vapor deposition, with the following technical parameters: temperature 50℃~150℃, vacuum degree 2.0×10-4Pa~4.0×10-4Pa, deposition time 30-300 minutes, and deposition rate 1g / min~10g / min.

[0054] The organic lithium is at least one of lithium stearate, lithium lactate, lithium acrylate, lithium citrate, and lithium acetate; the inorganic lithium is at least one of lithium fluoride, lithium carbonate, lithium oxide, and lithium nitride; the crosslinking agent is at least one of azodicarbonamide, azobisisobutyramidine hydrochloride, diethyl azodicarbonate, azobenzenesulfonic acid, azobisisobutyronitrile, and 4-aminoazobenzene; and the passivating agent is at least one of CoF3, MnF3, FeF3, VF3, TiF3, NiF2, FeF2, CuF2, CuF, SnF2, and AgF. The mass ratio of organic lithium, inorganic lithium, crosslinking agent, passivating agent, and silicon-carbon intermediate is (5-20):(5-20):(1-5):(1-5):500.

[0055] Heteroatom deposition on porous carbon cores can effectively reduce their surface activity and specific surface area, thereby reducing the occurrence of side reactions. Simultaneously, heteroatom modification helps guide the uniform deposition of nano-silicon within the porous carbon core, thereby improving the material's storage performance and suppressing gas generation.

[0056] Constructing a protective layer on the surface of a silicon-carbon intermediate using physical vapor deposition (PVD) serves a dual purpose: firstly, this coating improves the integrity of the core silicon-carbon intermediate, reducing direct exposure of nano-silicon to the electrolyte and thus suppressing gas generation; secondly, the protective layer contains an artificial SEI component composed of organic and inorganic lithium, which can replenish lithium-ion losses during charging and discharging, reduce side reactions, and enhance the lithium-ion diffusion rate. Furthermore, the introduction of a crosslinking agent creates a network structure in the outer layer, enhancing the structural stability of the coating and effectively suppressing volume expansion during charging and discharging, further reducing side reactions and gas generation.

[0057] Example 2 This embodiment prepares a silicon-carbon composite material using the method described in this application, including the following steps: Step S1: Porous carbon modification 1 kg of porous carbon was added to the rotary kiln, and nitrogen gas was introduced to purge the air from the tubes.

[0058] The furnace body is heated to 850°C in a nitrogen atmosphere.

[0059] While maintaining a stable temperature, pyridine gas was continuously introduced at a flow rate of 3 L / min for 150 minutes to modify the carbon material, resulting in modified porous carbon.

[0060] Step S2: Preparation of silicon-carbon intermediates Stop the flow of pyridine and lower the system temperature to 500°C.

[0061] Under a positive pressure of 0.12 MPa, a silane mixture consisting of silane and nitrogen in a volume ratio of 2:10 was introduced at a flow rate of 30 L / min for 75 minutes.

[0062] After the reaction was completed, the system was cooled to room temperature under an argon protective atmosphere to obtain a silicon-carbon intermediate.

[0063] Step S3: Silicon-carbon composite material coating treatment Weigh out 10 g of lithium stearate, 10 g of lithium fluoride, 3 g of azodicarbonamide and 3 g of CoF3 respectively, mix them evenly and use them as coating materials.

[0064] 500 g of the silicon-carbon intermediate obtained in step S2 was spread evenly on the bottom of the vapor phase furnace as a deposition substrate.

[0065] Deposition was performed using physical vapor deposition (PVD) under the following process conditions: Heating temperature: 100℃; System vacuum level: 3.0 × 10⁻⁶ -4 Pa; Deposition rate: 5 g / min; Deposition time: 150 minutes; Deposition thickness: 300 nm; After deposition, the final product is obtained – a silicon-carbon composite material.

[0066] Example 3 This embodiment uses the method for preparing silicon-carbon composite materials described in this application to prepare a silicon-carbon composite material, including the following steps: Step S1: Porous carbon modification 1 kg of porous carbon was added to the rotary kiln, and nitrogen gas was introduced to purge the air from the tubes.

[0067] The furnace body is heated to 600°C in a nitrogen atmosphere.

[0068] While maintaining a stable temperature, pyrrole gas was continuously introduced at a flow rate of 1 L / min for 300 minutes to obtain modified porous carbon.

[0069] Step S2: Preparation of silicon-carbon intermediates Stop the flow of pyrrole gas and lower the system temperature to 450°C.

[0070] Under a positive pressure of 0.1 MPa, a mixed gas consisting of silane and nitrogen in a volume ratio of 1:10 was introduced, with a flow rate of 10 L / min, for 100 minutes.

[0071] After the reaction was completed, the system was cooled to room temperature under an argon protective atmosphere to obtain a silicon-carbon intermediate.

[0072] Step S3: Silicon-carbon composite material coating treatment Weigh out 5 g of lithium lactate, 20 g of lithium carbonate, 1 g of azobisisobutyramidine hydrochloride and 1 g of MnF3 respectively, mix them evenly and use them as coating materials.

[0073] 500 g of the silicon-carbon intermediate obtained in step S1 was spread evenly on the bottom of the vapor phase furnace as a deposition substrate.

[0074] Deposition was performed using physical vapor deposition (PVD) under the following process conditions: Heating temperature: 50℃; System vacuum level: 2.0 × 10⁻⁶ -4 Pa; Deposition rate: 1 g / min; Deposition time: 300 minutes; Deposition thickness: 100 nm; After deposition, the final product is obtained – a silicon-carbon composite material.

[0075] Example 4 This embodiment uses the method for preparing silicon-carbon composite materials described in this application to prepare a silicon-carbon composite material, including the following steps: Step S1: Porous carbon modification 1 kg of porous carbon was added to the rotary kiln, and nitrogen was introduced to purge air from the system.

[0076] The furnace body is heated to 1000°C in a nitrogen atmosphere.

[0077] While maintaining a stable temperature, quinoline gas was continuously introduced at a flow rate of 5 L / min for 30 minutes to obtain modified porous carbon.

[0078] Step S2: Preparation of silicon-carbon intermediates Stop the flow of quinoline gas and lower the system temperature to 600°C.

[0079] Under a positive pressure of 0.15 MPa, a mixed gas consisting of dichlorosilane and nitrogen in a volume ratio of 3:10 is introduced, with a flow rate of 50 L / min, for 50 minutes.

[0080] After the reaction was completed, the system was cooled to room temperature under a nitrogen protective atmosphere to obtain a silicon-carbon intermediate.

[0081] Step S3: Silicon-carbon composite material coating treatment Weigh out 20 g of lithium acrylate, 5 g of lithium oxide, 5 g of diethyl azodicarbonate and 5 g of FeF3 respectively, mix them evenly and use them as coating materials.

[0082] 500 g of the silicon-carbon intermediate obtained in step S1 was spread evenly on the bottom of the vapor phase furnace as a deposition substrate.

[0083] Deposition was performed using physical vapor deposition (PVD) under the following process conditions: Heating temperature: 150℃; System vacuum level: 4.0 × 10⁻⁶ -4 Pa; Deposition rate: 10 g / min; Deposition time: 300 minutes; Deposition thickness: 500 nm; After deposition, the final product is obtained – a silicon-carbon composite material.

[0084] Comparative Example 1: Unlike Example 2, pyridine gas is not introduced in step S1, but otherwise it is the same as Example 1.

[0085] Comparative Example 2: The main difference between this comparative example and Example 2 is that, in step S3, physical vapor deposition is not used; instead, a liquid phase method is employed for coating. The specific preparation process is as follows: 10g of lithium stearate, 10g of lithium fluoride, 3g of azodicarbonamide and 3g of CoF3 were placed in 1000g of cyclohexane organic solvent and dispersed evenly to form a coating solution.

[0086] Add 500g of the silicon-carbon intermediate obtained in step S2 to the above solution and stir thoroughly to disperse it evenly.

[0087] The mixture was spray-dried to obtain a pre-coated powder.

[0088] The powder was heat-treated and carbonized at 800°C for 3 hours under an inert atmosphere to obtain a silicon-carbon composite material.

[0089] Comparative Example 3: Unlike Example 2, CoF3 is not added in step S3, but everything else is the same as in Example 1.

[0090] Comparative Example 4: The difference between this comparative example and Example 2 is that 10g of lithium stearate is not added in step S3, while the rest is the same as in Example 1.

[0091] Comparative Example 5: In this comparative example, lithium fluoride is not added in step S3, but everything else is the same as in Example 2.

[0092] Comparative Example 6: The difference between this comparative example and Example 2 is that in step S3, 30g of lithium stearate and 1g of lithium fluoride are used, while the rest is the same as in Example 1.

[0093] Comparative Example 7: Unlike Example 2, step S3 involves adding 50g of lithium fluoride; otherwise, it is the same as Example 1.

[0094] Scanning electron microscopy imaging test: Figure 2 The image shows a SEM image of the silicon-carbon composite material prepared in Example 2. The results show that the material exhibits a regular blocky structure with a uniform particle size distribution, mainly concentrated between 5 and 10 μm.

[0095] Performance testing of silicon-carbon composite materials: The silicon-carbon composite materials prepared in the examples and comparative examples were systematically characterized. The test items included: particle size, tap density, specific surface area, silicon grain size, powder resistivity, gas generation behavior, specific capacity, and initial coulombic efficiency.

[0096] The testing method is as follows: Powder resistivity: measured using a four-probe tester.

[0097] Coating integrity: The material surface was analyzed by Raman spectroscopy.

[0098] Gas production test: Accurately weigh m1g of powder material, immerse it in 10% sodium hydroxide aqueous solution, keep it at a constant temperature of 45℃ for 48h, measure the volume of gas produced V1, and calculate it according to the formula "Gas production = (V1 / m1) × 100%".

[0099] Other items: All tests were conducted in accordance with the methods specified in the national standard GB / T 38823-2020 "Silicon Carbon".

[0100] Table 1 According to the data in Table 1, Examples 2-4 show significant advantages over Comparative Examples 1-7 in key structural parameters such as tap density, specific surface area, silicon grain size, coating integrity, and powder resistivity. These structural features stem from the "core heteroatom doping + surface PVD coating" composite modification strategy adopted in this application, and the specific technical effects are as follows: Constructing a highly efficient conductive network enhances charge transport efficiency. Core heteroatom doping effectively modulates the electronic structure of porous carbon, enhancing intrinsic electronic conductivity. Simultaneously, the lithium salt component in the PVD coating forms an interface phase rich in highly ionic conductors after electrochemical activation. These two elements synergistically construct an "electron-ion" dual-continuous conductive network, significantly reducing powder resistivity and improving electrode rate performance and fast-charging capability.

[0101] Forming a dense coating layer enhances interface and structural stability. PVD technology achieves nanoscale thickness, uniformity, and density of artificial coating layers, with significantly better coverage integrity than traditional liquid-phase methods. This coating layer effectively blocks direct contact between the electrolyte and the highly active silicon-carbon core, greatly reducing side reactions, suppressing gas generation, and providing mechanical constraint on silicon volume expansion during cycling, thereby improving the structural integrity of the material.

[0102] The synergistic design of "core doping + surface coating" optimizes the overall electrochemical performance, improving conductivity and stabilizing the interface structure, while jointly promoting the comprehensive improvement of silicon-carbon composite materials in terms of specific capacity, first coulombic efficiency and long cycle life, demonstrating significant system performance advantages.

[0103] Example 5 The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-7 were used to assemble coin cells to evaluate their electrochemical performance and structural stability. The specific methods are as follows: Electrode preparation: The silicon-carbon composite materials were mixed with binder (LA132), conductive agent (SP) and solvent (NMP) in a mass-volume ratio of 95g : 1g : 4g : 220mL. After stirring and slurry preparation, the mixture was uniformly coated onto copper foil, dried and rolled to obtain the negative electrode sheet.

[0104] Battery Assembly: In an argon-filled glove box, a coin cell was assembled using the prepared negative electrode as the working electrode, a lithium metal sheet as the counter electrode, and a polypropylene (PP) membrane as the separator. The electrolyte was a 1 mol / L LiPF6 solution, and the solvent was a 1:1 volume mixture of EC and DEC.

[0105] Performance testing: Electrochemical performance: Charge and discharge tests were conducted on the Wuhan Landian CT2001A battery testing system, with a voltage range of 0.005–2.0 V and a charge / discharge rate of 0.1C. The results are shown in Table 2.

[0106] Full charge expansion rate: The initial thickness of the negative electrode sheet after rolling (D1) was measured. After the battery was charged to 100% SOC, it was dissected and the thickness of the negative electrode sheet under full charge (D2) was measured. The full charge expansion rate was calculated according to the formula "full charge expansion rate = (D2-D1) / D1 × 100%". The results are shown in Table 2.

[0107] Table 2 As shown in Table 2, the silicon-carbon composite materials prepared in Examples 2-4 of this application outperform the samples in Comparative Examples 1-7 in both initial coulombic efficiency and full charge expansion rate. This performance advantage mainly stems from the synergistic optimization of the material structure and composition. The dense coating effectively suppresses volume expansion. The lithium compound coating layer constructed on the material surface by physical vapor deposition (PVD) technology has the characteristics of dense structure, uniformity and strong bonding. It can form a stable mechanical constraint on the outer layer, effectively buffering the volume expansion of silicon during lithium intercalation, thereby significantly reducing the full charge expansion rate of the electrode.

[0108] Multidimensional conductive networks improve charge transport efficiency The porous carbon core is doped with heteroatoms to enhance electronic conductivity; at the same time, the lithium compounds in the outer shell form an interface phase with high ionic conductivity after electrochemical activation. Together, they construct a conductive network with synergistic "electron-ion" dual pathways, which improves the apparent diffusion coefficient of lithium ions and thus improves the material's first coulombic efficiency and rate performance.

[0109] Pouch cell fabrication and performance testing The silicon-carbon composite materials corresponding to the above embodiments and comparative examples were mixed with artificial graphite at a mass ratio of 10% to prepare negative electrode sheets as negative electrode active materials. Ternary materials (LiNi) were also used. 0.8 Co 0.1 Mn 0.1 Using O2 as the positive electrode and Celgard 2400 as the separator, a pouch cell with a rated capacity of 5 Ah is assembled. The electrolyte is a 1.3 mol / L LiPF6 solution, and the solvent is EC / DEC (volume ratio 1:1).

[0110] The following performance tests were conducted on each pouch battery, and the results are summarized in Table 3.

[0111] a. High-temperature storage performance test Charge the battery to full capacity at 45°C, then discharge it to 2.5V.

[0112] Charge it to 4.2 V at a rate of 0.33 C, and record its capacity A0.

[0113] Store a fully charged battery at 45°C for 30 days.

[0114] After storage, discharge at a rate of 0.33 C, record the discharge capacity A1, and calculate the charge retention rate (A1 / A0×100%).

[0115] Then charge at a rate of 0.33 C, record the charging capacity A2, and calculate the capacity recovery rate (A2 / A1× 100%).

[0116] b. Ratio Performance Testing The constant current ratio of the battery at a 2C rate is calculated using the following formula: Constant current ratio = 2C constant current capacity / (2C constant current capacity + 0.1C constant voltage compensation capacity) c. Cyclic performance testing Under an environment of 25 ± 3.0℃, constant current charge-discharge tests were conducted at a rate of 1.0 C within a voltage range of 2.5 V–4.2 V, and the capacity retention rate of the battery after 500 cycles was recorded.

[0117] Table 3 As shown in Table 3, the soft-pack lithium-ion batteries assembled using the silicon-carbon composite materials of Examples 2-4 exhibit significantly better performance than those of Comparative Examples 1-7 in terms of high-temperature storage, rate capability, and cycle life. This performance advantage is mainly attributed to the following material structural features: High specific surface area promotes electrolyte wetting The material has a suitable high specific surface area, which effectively improves the electrode's liquid absorption capacity and electrolyte wetting efficiency, providing a sufficient working interface for ion transport.

[0118] Low resistance and high diffusion coefficient work together to improve fast charging capability The material has low powder resistivity and high lithium-ion diffusion coefficient, which together form an efficient charge transport path and significantly improve rate performance, specifically manifested in a higher constant current ratio in 2C testing.

[0119] Dense coating inhibits interfacial side reactions The uniform and complete surface coating effectively blocks direct contact between the active material and the electrolyte, reducing side reactions under high temperature conditions, thereby significantly improving the battery's charge retention rate and capacity recovery rate.

[0120] The foregoing has provided a detailed description of a silicon-carbon composite material, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0121] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with the claims of this application shall still fall within the scope of this application.

Claims

1. A method for producing a silicon-carbon composite material, characterized by, The method comprises the following steps, Step S1: adding porous carbon into a rotary furnace, discharging air into the rotary furnace, heating the rotary furnace to 600-1000℃, then introducing heteroatomic gas for 30-300 minutes to obtain modified porous carbon; Step S2: keeping the temperature of the rotary furnace at 450-600℃, introducing silane mixed gas, cooling the temperature of the rotary furnace to room temperature after 10-200 minutes to obtain a silicon-carbon intermediate; Step S3: mixing organic lithium, inorganic lithium, cross-linking agent and passivation agent to obtain coating material, depositing the coating material on the surface of the silicon-carbon intermediate by physical vapor deposition to obtain the silicon-carbon composite material.

2. The method for preparing a silicon-carbon composite material according to claim 1, wherein The mass-volume ratio of the porous carbon, the heteroatomic gas and the silane mixed gas is 1 kg: (1-10) L: (500-2000) L.

3. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, The mass ratio of the organic lithium, the inorganic lithium, the cross-linking agent, the passivation agent and the silicon-carbon intermediate is (5-20):(5-20):(1-5):(1-5):

500.

4. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, The heteroatomic gas is organic heteroatomic gas, which is vaporized from at least one of pyridine, quinoline, pyrimidine, pyrrole, indole, imidazole, purine, furan and thiophene. Alternatively, the silane mixed gas is mixed from at least one of monosilane, disilane, dichlorosilane, trichlorosilane, silicon tetrachloride and silicon tetrafluoride and nitrogen, and the volume ratio is (1-3):

10.

5. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, The organic lithium is at least one of lithium stearate, lithium lactate, lithium acrylate, lithium citrate and lithium acetate.

6. The method of claim 1, wherein the silicon-carbon composite material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon composite material. The inorganic lithium is at least one of lithium fluoride, lithium carbonate, lithium oxide and lithium nitride. Alternatively, the cross-linking agent is at least one of azobisformamide, azobisdimethylamid hydrochloride, azobisdimethylate, azobenzenesulfonic acid, azobisdimethyl nitrile and 4-aminoazobenzene.

7. The method for preparing the silicon-carbon composite material as described in claim 1, characterized in that, The passivation agent is at least one of CoF3, MnF3, FeF3, VF3, TiF3, NiF2, FeF2, CuF2, CuF, SnF2 and AgF.

8. The method of claim 1, wherein the silicon-carbon composite material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; heating the mixture to form a silicon-carbon composite material; and annealing the silicon-carbon composite material. In step S3, physical vapor deposition is performed by vacuum evaporation technique, wherein the temperature is 50-150°C, the vacuum degree is 2.0 x 10 -4 Pa, the deposition time is 30-300 minutes, and the deposition rate is 1-10 g / min. - 4 Pa, the deposition time is 30-300 minutes, and the deposition rate is 1-10 g / min.

9. A silicon-carbon composite material, characterized by, The composite material is prepared by the method of any one of claims 1-8, which comprises an inner core and an outer shell, the inner core is a composite of nano-silicon and heteroatoms deposited on the surface of porous carbon, and the outer shell is amorphous carbon and a composite deposited on the amorphous carbon by physical vapor deposition after mixing organic lithium, inorganic lithium, cross-linking agent and passivation agent.

10. The silicon-carbon composite of claim 9, wherein, The thickness of the outer shell is 100-500 nm.

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