Fluorinated silver composite silicon-carbon material, and preparation method and application thereof

Abstract

This invention provides a silver fluoride composite silicon-carbon material, its preparation method, and its application, relating to the field of silicon-carbon material technology. The preparation method includes: mixing a silicon-carbon matrix, a silver source, and a carbon source in a liquid environment, followed by evaporating the solvent to obtain a composite precursor; heat-treating the composite precursor in an inert atmosphere at 400℃-600℃ to obtain a composite intermediate; and fluorinating the composite intermediate to obtain the silver fluoride composite silicon-carbon material. This invention, by coating the surface of the silicon-carbon matrix with a buffer layer containing nano-silver fluoride particles, helps to constrain the volume expansion of silicon during cycling and maintain the integrity of the electrode structure. Furthermore, the heterojunction formed between the buffer layer and the silicon-carbon matrix can reduce interfacial impedance and induce the formation of a dense lithium fluoride-based SEI film, effectively improving structural stability. Simultaneously, the formation of C-F bonds enhances interfacial bonding and promotes lithium-ion migration, contributing to improved cycling performance.

Description

Technical Field

[0001] This invention relates to the field of silicon-carbon materials technology, and in particular to a silver fluoride composite silicon-carbon material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and large-scale energy storage power stations, lithium batteries, as efficient and clean energy storage carriers, are seeing their application scenarios continuously expand. However, the commonly used anode material for lithium batteries is currently graphite, whose theoretical specific capacity of 372 mAh / g severely restricts the development of high-energy-density, high-performance lithium batteries. Silicon, due to its higher theoretical specific capacity, has become the most promising alternative anode material. However, in practical applications, silicon anodes undergo drastic volume expansion during charging and discharging, leading to the pulverization and shedding of the surface active material. This also continuously damages the stability of the SEI film, causing continuous decomposition of the electrolyte and irreversible consumption of lithium ions, resulting in rapid capacity decay and shortened cycle life.

[0003] To address the volume expansion issue of silicon anodes during charging and discharging, common methods include silicon material nanofiberization, composite structure design, and interface engineering. In silicon material nanofiberization, silicon is fabricated into nanoparticles, nanowires, or nanofilms, utilizing the nanoscale effect to shorten the lithium-ion diffusion path and using the gaps between particles to buffer volume changes. In composite structure design, the most common approach is to combine silicon with carbon materials to construct silicon-carbon composites, using the carbon matrix to improve overall conductivity and provide elastic support space for silicon volume expansion. In interface engineering, the main approach involves coating or pre-lithiating the surface of silicon materials to enhance the stability of the SEI film and reduce side reactions.

[0004] However, while silicon nanomaterials can alleviate the volume expansion problem to some extent, their preparation process is relatively complex and costly. The high specific surface area of ​​silicon nanoparticles can also exacerbate side reactions, leading to low initial efficiency. In silicon-carbon composites, due to the interfacial bonding problem between silicon and carbon, interfacial delamination is prone to occur during long-term cycling. In silicon material interface engineering, the uniformity, density, and electrochemical performance of the surface coating layer directly affect the overall cycling performance of the material. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a silver fluoride composite silicon-carbon material, its preparation method, and its application. By coating the surface of a silicon-carbon matrix with a buffer layer containing nano-silver fluoride particles, it helps to constrain the volume expansion of silicon during cycling and maintain the integrity of the electrode structure. In addition, the heterojunction formed by the buffer layer and the silicon-carbon matrix can reduce the interfacial impedance and induce the formation of a dense lithium fluoride-based SEI film, which can effectively improve the structural stability. At the same time, the formation of CF bonds can also enhance the interfacial bonding force and promote the migration of lithium ions, which helps to improve cycling performance.

[0006] In a first aspect, the present invention provides a method for preparing a silver fluoride composite silicon-carbon material, comprising: mixing a silicon-carbon matrix, a silver source, and a carbon source in a liquid environment and then evaporating the solvent to obtain a composite precursor; heat-treating the composite precursor in an inert atmosphere at 400℃-600℃ to obtain a composite intermediate; and fluorinating the composite intermediate to obtain a silver fluoride composite silicon-carbon material.

[0007] Optionally, the silver source includes one of silver acetate, silver nitrate, silver oxide, silver chloride, and silver sulfate.

[0008] Optionally, the carbon source includes one of citric acid, glucose, urea, and phenolic resin.

[0009] Optionally, the liquid environment includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, dichloromethane, and N,N-dimethylacetamide.

[0010] Optionally, the mass ratio of the silver source to the carbon source is 8:(5-7).

[0011] Optionally, the mass concentration of the silver source in the liquid environment is 0.3%-1.5%.

[0012] Optionally, the mass concentration of the silicon-carbon matrix in the liquid environment is 5%-15%.

[0013] Optionally, the solvent can be evaporated at 50°C-80°C.

[0014] Optionally, the solvent is evaporated and then dried to obtain the composite precursor.

[0015] Optionally, a dispersant is dissolved in the liquid environment.

[0016] Optionally, the concentration of the dispersant in the liquid environment is 1wt%-10wt%.

[0017] Optionally, the dispersant includes one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

[0018] Optionally, after the dispersant is dissolved in a liquid environment by stirring, a silicon-carbon matrix, a silver source, and a carbon source are added and ultrasonically mixed.

[0019] Optionally, the composite precursor is heated at a rate of 1℃ / min to 20℃ / min.

[0020] Optionally, heat treatment for 1-3 hours.

[0021] Optionally, the inert atmosphere includes either an argon atmosphere or a nitrogen atmosphere.

[0022] Optionally, the flow rate of the inert atmosphere is 1 L / min to 20 L / min.

[0023] Optionally, the pressure of the inert atmosphere is 0.1 MPa-1 MPa.

[0024] Optionally, the composite intermediate is mixed with a fluorine source and then fluorinated at high temperature in a protective atmosphere at 200℃-400℃ to obtain silver fluoride composite silicon-carbon material.

[0025] Optionally, the fluorine source includes at least one of ammonium bifluoride, trifluoroacetic acid, and ammonium fluoride.

[0026] Optionally, the mass ratio of the composite intermediate to the fluorine source is 1:(0.01-0.15).

[0027] Optionally, fluorination can be carried out at high temperature for 2-4 hours.

[0028] Optionally, the method for preparing the silicon-carbon matrix includes: depositing nano-silicon within a porous carbon framework to obtain a silicon-carbon precursor; graphitizing the silicon-carbon precursor at 1200℃-1400℃ for 1 min-5 min to obtain a silicon-carbon intermediate; and surface modifying the silicon-carbon intermediate to obtain a silicon-carbon matrix.

[0029] Optionally, the porous carbon framework includes a porous carbon framework doped with heterogeneous elements or undoped.

[0030] Optionally, the pore size of the porous carbon framework is 1 nm to 100 nm.

[0031] Optionally, the heteroelement includes one of nitrogen, sulfur, boron, phosphorus, and fluorine.

[0032] Alternatively, the porous carbon framework can be chemically vapor-deposited in a silicon source gas.

[0033] Optionally, the silicon-carbon intermediate is subjected to surface silane treatment to obtain a silicon-carbon matrix.

[0034] Secondly, the present invention also provides a silver fluoride composite silicon-carbon material prepared by any of the above-mentioned optional preparation methods, comprising a silicon-carbon matrix and a composite buffer layer formed on the surface of the silicon-carbon matrix, wherein the composite buffer layer comprises a carbon-based coating layer and nano-silver fluoride particles doped in the carbon-based coating layer.

[0035] Thirdly, the present invention also provides an application of silver fluoride composite silicon-carbon material prepared by any of the above-mentioned optional preparation methods in lithium batteries.

[0036] The method for preparing silver fluoride composite silicon-carbon material provided by this invention has at least one of the following beneficial technical effects compared with the prior art: 1. By loading a silver source and a carbon source together on the surface of a silicon-carbon matrix, the carbon source undergoes pyrolysis and carbonization during heat treatment, thereby forming a continuous and dense carbon-based coating layer on the surface of the silicon-carbon matrix. This layer can not only uniformly coat the surface of the silicon-carbon matrix, but also interlock with the carbon skeleton in the silicon-carbon matrix, thereby improving the interfacial bonding stability and reducing the interfacial impedance. At the same time, the silver source dispersed in the coating layer is reduced in situ by carbothermal treatment at high temperature, generating silver nanoparticles embedded in the coating layer. After fluorination, uniformly dispersed and stably bonded silver fluoride nanoparticles are formed in the coating layer. 2. By coating the surface of the silicon-carbon matrix with a buffer layer containing silver fluoride nanoparticles, the volume expansion of silicon during cycling can be constrained, maintaining the structural integrity of the electrode structure during cycling. At the same time, the interlocking between the buffer layer and the carbon skeleton of the silicon-carbon matrix forms a heterojunction that helps reduce interfacial impedance and induces the formation of a dense lithium fluoride-based SEI film, which helps improve the stability of the electrode structure. Furthermore, CF bonds can be generated at the interface, further enhancing the interfacial bonding force, promoting lithium ion movement, and improving cycling performance. Attached Figure Description

[0037] Figure 1 A flowchart illustrating the preparation method of the silver fluoride composite silicon-carbon material provided by the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the silver fluoride composite silicon-carbon material prepared in Example 1 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0039] See Figure 1 This invention provides a method for preparing silver fluoride composite silicon-carbon material, comprising the following steps: S1. The silicon-carbon matrix, silver source and carbon source are mixed in a liquid environment and the solvent is evaporated to obtain the composite precursor. S2. The composite precursor is heat-treated in an inert atmosphere at 400℃-600℃ to obtain the composite intermediate. S3. Fluoride the composite intermediate to obtain silver fluoride composite silicon-carbon material.

[0040] In fact, the preparation method provided by the present invention involves coating a silver source and a carbon source together on the surface of a silicon-carbon matrix. After high-temperature heat treatment, the carbon source decomposes to form a carbon framework, and the silver source is reduced by carbothermal reduction to generate silver nanoparticles. At the same time, the silver nanoparticles can be uniformly doped into the carbon framework, which helps the silver fluoride nanoparticles to be uniformly distributed on the surface of the silicon-carbon matrix after fluorination treatment. It can also improve the structural stability of the silver fluoride nanoparticles generated by in-situ fluorination within the carbon framework.

[0041] In some embodiments, the silver source used in step S1 includes one of silver acetate, silver nitrate, silver oxide, silver chloride, and silver sulfate. In practice, the silver source can be a soluble silver salt, such as silver acetate, silver nitrate, silver chloride, or silver sulfate; or it can be insoluble silver-containing particles, such as nano-sized silver oxide. Specifically, soluble silver salts need to dissolve in a liquid environment to form a stable and homogeneous solution, while when using insoluble silver-containing particles, their particle size can be 10 nm-500 nm, and they can be uniformly dispersed in a liquid environment using methods such as ultrasonic dispersion.

[0042] In some embodiments, the silver source used in step S1 is preferably a soluble silver source, which can improve the dispersion uniformity of silver on the surface of the composite precursor, thereby improving the dispersion uniformity of the silver fluoride nanoparticles on the surface of the final silicon-carbon material. In fact, when the silver source is selected as insoluble silver-containing particles, surface treatment methods commonly used in the art can be used to improve the dispersion uniformity of insoluble silver-containing particles in a liquid environment, such as using a coupling agent to treat the silver-containing particles to prevent them from agglomerating and settling in a liquid environment.

[0043] In some embodiments, the carbon source used in step S1 includes one of citric acid, glucose, urea, and phenolic resin. In practice, a soluble carbon source is preferred, such as a carbon-containing organic compound or a polymer, which dissolves the carbon source in a liquid environment to form a carbon-containing solution. This facilitates the formation of a highly uniform mixed solution with the silver source, thereby improving the uniformity and density of the carbon skeleton formed on the silicon-carbon matrix surface after heat treatment.

[0044] In fact, the structure and properties of the carbon coating layer formed on the surface of the composite silicon-carbon material vary depending on the type of carbon source used in step S1. For example, when urea is used as a carbon source and composited on the surface of the silicon-carbon matrix, and then carbonized by heat treatment, the urea undergoes pyrolysis and polycondensation, thereby generating graphitic carbon nitride (g-C3N4) in situ on the surface of the silicon-carbon matrix. This allows the nitrogen-rich g-C3N4 to anchor the silicon-carbon particles and induce the formation of a stable interface film, while effectively improving the flexibility of the buffer layer and its ability to transport lithium ions.

[0045] In some embodiments, the liquid environment used in step S1 includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, dichloromethane, and N,N-dimethylacetamide. In practice, the liquid environment used must be sufficient to dissolve the carbon source without reacting with the carbon source, silver source, or silicon-carbon matrix. Furthermore, the mass concentration of the silver source in the liquid environment is 0.3%-1.5%, and the mass concentration of the silicon-carbon matrix is ​​5%-15%. In fact, adjusting the concentration of the silver source in the liquid environment helps to adjust the loading of silver fluoride nanoparticles on the composite silicon-carbon surface. Further, the mass ratio of the silver source to the carbon source is 8:(5-7).

[0046] In some embodiments, in step S1, the silicon-carbon material can be first dispersed in a portion of the liquid environment to form a silicon-carbon suspension, and the silver source and carbon source can be stirred, dispersed, and / or dissolved in the remaining liquid environment to form a carbon-silver mixture. Then, the silicon-carbon suspension and the carbon-silver mixture are uniformly mixed. Further, the mass concentration of the silicon-carbon matrix in the silicon-carbon suspension can be 15%-20%, and the mass concentration of the silver source in the carbon-silver mixture can be 1%-3%. Thus, the silicon-carbon suspension and the carbon-silver mixture can be mixed at a mass ratio of 1:(0.5-0.8).

[0047] In some embodiments, when mixing the silicon-carbon matrix, silver source, and carbon source in a liquid environment in step S1, commonly used dispersion-promoting methods in the art can be employed, such as mechanical stirring, physical vibration, and ultrasonic treatment. Furthermore, after mixing in the liquid environment, the solvent can be evaporated at 50°C-80°C, and the mixture can be dried to constant weight to obtain the composite precursor. In practice, the temperature used for evaporating the solvent is necessary to ensure sufficient evaporation of the solvent in the liquid environment.

[0048] In fact, the liquid environment used in step S1 also contains 1wt%-10wt% of a dispersant. This dispersant helps improve the uniformity of the silicon-carbon matrix dispersion in the liquid environment, preventing the silicon-carbon material from agglomerating and settling during solvent evaporation, thereby improving the uniformity of the coating layer on the surface of the silicon-carbon matrix. Furthermore, the dispersant used includes one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol. In fact, during solvent evaporation, the polymeric dispersant helps prevent component segregation of the silver salt dispersion and can be completely carbonized and participate in the construction of the carbon framework during heat treatment.

[0049] In some embodiments, in step S1, the dispersant can be first stirred and dissolved in a liquid environment to form a dispersant solution, and then the silicon-carbon matrix, silver source, and carbon source can be added to the dispersant solution for ultrasonic mixing. In fact, ultrasonic treatment helps to eliminate microbubbles adhering to the surface of the silicon-carbon matrix, and can promote the dispersant solution to fully wet the surface and pores of the silicon-carbon matrix, which helps to improve the dispersion uniformity of the carbon source adhering to the surface during solvent evaporation.

[0050] In some embodiments, the silicon-carbon matrix used in step S1 can be a commercially available conventional product, such as silicon-based anode materials (models GS45, GS50, and GS60) purchased from Shanghai Shanshan Technology Co., Ltd., or a silicon-carbon matrix prepared using methods commonly used in the art, such as chemical vapor deposition, mechanical ball milling, and spray drying. In fact, coating the surface of the silicon-carbon matrix with a carbon buffer layer containing silver fluoride nanoparticles helps to slow down the volume expansion of the silicon material during cycling, thereby improving the structural stability of the electrode material and thus enhancing electrochemical performance.

[0051] Furthermore, the method for preparing the silicon-carbon matrix used in step S1 may include: Z1. Silicon-carbon precursors were prepared by depositing nano-silicon within a porous carbon framework. Z2. The silicon-carbon precursor was graphitized at 1200℃-1400℃ for 1 min-5 min to obtain the silicon-carbon intermediate. Z3. Surface modification of silicon-carbon intermediates to obtain silicon-carbon matrix.

[0052] In fact, when preparing silicon-carbon matrix, depositing nano-silicon within a porous carbon framework can effectively limit the volume expansion of silicon and prevent its aggregation by confining it with the carbon framework. At the same time, short-term graphitization treatment helps to improve the electronic conductivity of the silicon-carbon matrix and the positional stability of the nano-silicon within the matrix. Surface modification helps to improve the surface activity of the silicon-carbon matrix, thereby improving the uniformity of carbon and silver sources coated on its surface.

[0053] In some embodiments, the porous carbon framework used in step Z1 includes a heteroelement-doped or undoped porous carbon framework. In fact, introducing heteroelement doping into the porous carbon framework helps improve its intrinsic electronic conductivity and enhances its surface reactivity, thereby improving its interfacial bonding with nano-silicon and effectively suppressing the peeling off of nano-silicon during cycling. Specifically, heteroelement doping in the porous carbon framework can be performed using doping techniques commonly used in the art. Specifically, heteroelements that can be doped into the porous carbon framework include one of nitrogen, sulfur, boron, phosphorus, and fluorine.

[0054] In some embodiments, the pore size of the porous carbon framework used in step Z1 is 1 nm-100 nm. In fact, by depositing nano-silicon within a porous carbon framework with nanoscale pores, the nano-silicon particles can be effectively constrained and buffered, while also facilitating the impregnation of the silver and carbon sources into the pores and surface of the porous carbon framework in step S1. Specifically, the porous carbon framework used in step Z1 can be spherical porous carbon, and can use commercially available conventional products, such as porous carbon frameworks purchased from Kingboard Carbon Co., Ltd. with brand names KBC / PC-1, KBC / PC-2, and KBC / PC-3, or prepared using methods commonly used in the art.

[0055] In some embodiments, chemical vapor deposition (CVD) can be performed on the porous carbon framework in a silicon source gas in step Z1. Specifically, the silicon source gas used includes one of silane, dichlorosilane, and dichlorosilane. Further, the CVD process includes: heating the porous carbon framework to a target temperature, passing it through a silicon source gas and an inert carrier gas, causing the silicon source gas to thermally decompose on the surface and inside the pores of the porous carbon framework, thereby depositing nano-silicon, stopping the passage of silicon source gas, holding at the temperature, and then cooling to obtain a silicon-carbon precursor. In practice, the target temperature is related to the decomposition temperature of the silicon source gas used, and the silicon source concentration after mixing the silicon source gas and the inert carrier is 1 vol%-10 vol.

[0056] In some embodiments, after depositing nano-silicon in a silicon source gas via chemical vapor deposition in step Z1, a carbon-containing gas is then introduced to deposit an amorphous carbon layer on the surface via chemical vapor deposition. This helps to improve the structural stability of the nano-silicon within the porous carbon framework. At the same time, when the nano-silicon expands in volume, the amorphous carbon layer on its surface can effectively absorb the expansion stress, preventing the nano-silicon particles from breaking during cycling. Furthermore, the amorphous carbon framework and the porous carbon framework can be stably connected to form a connected three-dimensional conductive network, thereby improving electron transport efficiency.

[0057] In some embodiments, in step Z2, the silicon-carbon precursor is transferred into the furnace chamber of a tube furnace. After gas replacement with a protective gas, the precursor is subjected to a short-term heat treatment at 1200°C-1400°C to graphitize its surface. This helps improve the conductivity of the silicon-carbon matrix and further enhances the bonding stability between the amorphous carbon layer and the porous carbon framework in the precursor. In practice, the protective gas used includes either argon or helium, and the pressure during the short-term graphitization treatment can be standard atmospheric pressure.

[0058] In some embodiments, the silicon-carbon intermediate can be surface-silanized in step Z3 to obtain a silicon-carbon matrix. This improves the uniformity of the adhesion of the silver and carbon sources on the surface of the silicon-carbon matrix, thereby enhancing the bonding stability between the two interface layers in the silver fluoride silicon-carbon composite material. Simultaneously, the active groups grafted onto the surface of the silicon-carbon matrix during heat treatment do not introduce impurities. Specifically, a silane coupling agent, such as KH550 or KH560, can be used for surface silane treatment. Further, during silane treatment, the material can be impregnated and dispersed in an environment of 50°C-60°C with stirring / ultrasound, followed by separation and drying.

[0059] In some embodiments, the inert atmosphere used in step S2 includes either an argon atmosphere or a nitrogen atmosphere, with a flow rate of 1 L / min-20 L / min and a pressure of 0.1 MPa-1 MPa. In practice, during the heat treatment in a high-temperature, inert atmosphere, the carbon source in the coating layer composed of a carbon source and a silver source, which coats the surface of the composite precursor, undergoes pyrolysis to form a carbon-based coating layer. Simultaneously, during pyrolysis, a carbothermic reduction reaction occurs between the silver source and the carbon framework to generate silver nanoparticles. These silver nanoparticles can then be embedded in the carbon framework of the carbon-based coating layer, forming a uniformly dispersed and stable composite buffer layer.

[0060] In some embodiments, during step S2, the composite intermediate can be pre-transferred into the furnace chamber of a tube furnace. After multiple gas replacements of the furnace chamber by introducing inert gas, the tube furnace is heated at a rate of 1°C / min-20°C / min and then heat-treated at 400°C-600°C for 1-3 hours. After cooling to room temperature with the furnace, the composite intermediate is obtained. In practice, the composite intermediate includes a silicon-carbon matrix and a composite intermediate formed on the surface of the silicon-carbon matrix. The composite intermediate consists of a carbon-based coating layer and silver nanoparticles doped within the carbon-based coating layer.

[0061] In some embodiments, during step S3, the composite intermediate and a fluorine source are mixed at a mass ratio of 1:(0.01-0.15), and then fluorinated at a protective atmosphere at 200°C-400°C for 2-4 hours to obtain a silver fluoride composite silicon-carbon material. In fact, during the high-temperature fluorination process, the fluorine source can release active fluorine species and react with the nano-silver particles on the surface of the composite intermediate to generate silver fluoride nanoparticles in situ. These silver fluoride nanoparticles then form a continuous conductive network on the surface of the silicon-carbon material with the carbon coating layer, which is beneficial for promoting lithium-ion migration and thus improving the cycle performance of the battery. Simultaneously, silver fluoride can participate in the formation of a more stable SEI film, contributing to improved battery cycle life. In fact, the fluorine source used in step S3 includes at least one of ammonium hydrogen fluoride, trifluoroacetic acid, and ammonium fluoride.

[0062] Furthermore, the present invention also provides a silver fluoride composite silicon-carbon material prepared by the preparation method in any of the above embodiments, comprising a silicon-carbon matrix and a composite buffer layer formed on the surface of the silicon-carbon matrix, wherein the composite buffer layer comprises a carbon-based coating layer and nano-silver fluoride particles doped in the carbon-based coating layer. In addition, the present invention also provides an application of the above-mentioned silver fluoride composite silicon-carbon material in lithium batteries.

[0063] Preparation Example 1: A method for preparing a silicon-carbon matrix, comprising the following steps: Z1. The porous carbon framework (KBC / PC-1 from Jinbo Co., Ltd.) was transferred to the CVD reaction chamber. After purging with argon, the temperature was increased to 600℃ at 10℃ / min. Then, a mixed gas containing 5 vol% silane was introduced and kept at this temperature for 2 hours to allow the silane to undergo thermal decomposition in the reaction chamber and deposit nano-silicon in the porous carbon framework. After stopping the introduction of silane, the temperature was increased to 850℃ at a rate of 5℃ / min. Then, a mixed gas containing 10 vol% acetylene was introduced and kept at this temperature for 2 hours to deposit an amorphous carbon layer on the surface of the porous carbon framework. After stopping the introduction of acetylene, the furnace was cooled to room temperature in an argon atmosphere to obtain the silicon-carbon precursor. Z2. The temperature in the reaction chamber of the chemical vapor deposition equipment is raised to 1200℃ at a rate of 20℃ / min, held at that temperature for 3min for short-term graphitization treatment, and then cooled to room temperature to obtain a silicon-carbon intermediate. Z3. The silicon-carbon intermediate was ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 0.05 g / mL to prepare a mixed suspension. KH550 silane coupling agent (the mass ratio of silicon-carbon intermediate to KH550 is 1:0.18) was added to the mixed suspension and stirred to dissolve. After ultrasonic dispersion in a 60℃ water bath for 15 min, the mixture was filtered and separated. After drying at 50℃, the silicon-carbon matrix was obtained.

[0064] Preparation Example 2: A method for preparing a silicon-carbon matrix, which differs from Preparation Example 1 in that step Z2 is not performed, and in step Z3 the silicon-carbon precursor obtained in step Z1 is subjected to surface silanization treatment to obtain the silicon-carbon matrix.

[0065] Preparation Example 3: A method for preparing a silicon-carbon matrix, which differs from Preparation Example 1 in that step Z3 is not performed, and the silicon-carbon intermediate obtained in step Z2 is the silicon-carbon matrix.

[0066] Example 1: A method for preparing a silver fluoride composite silicon-carbon material, comprising the following steps: S1. The silicon-carbon matrix prepared in Preparation Example 1 was added to anhydrous ethanol and ultrasonically dispersed to obtain a silicon-carbon suspension with a concentration of 15%. Silver nitrate crystals and urea were mixed at a mass ratio of 4:3 and added to anhydrous ethanol to obtain a carbon-silver mixture with a silver nitrate concentration of 2%. The silicon-carbon suspension and the carbon-silver mixture were mixed at a mass ratio of 1:0.6, and 6% polyvinylpyrrolidone (PVP, Boai Xinkaiyuan Pharmaceutical K30) was added and ultrasonically mixed. The mixture was stirred in a 70°C water bath for 3 hours until the anhydrous ethanol evaporated to dryness. The solid was then dried in a 70°C forced-air drying oven for 12 hours to obtain the composite precursor. S2. The composite precursor is transferred to the furnace chamber of a tube furnace. Argon gas is introduced for gas circulation and replacement. The flow rate of argon gas is controlled at 10 L / min and the gas pressure is stabilized at 0.5 MPa. The tube furnace is heated to 500℃ at a rate of 10℃ / min and then heat-treated for 2 hours. After cooling to room temperature with the furnace, the composite intermediate is obtained. S3. The composite intermediate and ammonium bifluoride are mixed at a mass ratio of 1:0.1 and put into a ball mill jar. After ball milling for 3 hours in an argon atmosphere with a ball-to-material ratio of 5:1, the ball-milled mixture is transferred to a high-temperature tube furnace. The temperature is raised to 300°C at a rate of 10°C / min in an argon atmosphere and held for 3 hours. Then, the mixture is cooled to room temperature in the furnace to obtain silver fluoride composite silicon-carbon material.

[0067] Example 2: A method for preparing a silver fluoride composite silicon-carbon material, which differs from Example 1 in that the silicon-carbon matrix obtained in Preparation Example 2 is used in step S1.

[0068] Example 3: A method for preparing a silver fluoride composite silicon-carbon material, which differs from Example 1 in that the silicon-carbon matrix obtained in Preparation Example 3 is used in step S1.

[0069] Example 4: A method for preparing a silver fluoride composite silicon-carbon material, which differs from Example 1 in that, in step S1, silicon-carbon material of model GS45 from Shanghai Shanshan Technology Co., Ltd. is used as the silicon-carbon matrix.

[0070] Example 5: A method for preparing a silver fluoride composite silicon-carbon material, which differs from Example 1 in that, in step S1, silver nitrate crystals and glucose are mixed in anhydrous ethanol at a mass ratio of 4:3 to obtain a carbon-silver mixture with a silver nitrate concentration of 2%.

[0071] Example 6: A method for preparing silver fluoride composite silicon-carbon material, which differs from Example 1 in that, in step S2, the tube furnace is heated to 400°C at a rate of 10°C / min and then heat-treated for 2 hours.

[0072] Example 7: A method for preparing silver fluoride composite silicon-carbon material, which differs from Example 1 in that, in step S2, the tube furnace is heated to 600°C at a rate of 10°C / min and then heat-treated for 2 hours.

[0073] Comparative Example 1: A method for preparing a nano-silver composite silicon-carbon material, which differs from Example 1 in that step S3 is not performed, and the composite intermediate obtained in step S2 is the nano-silver composite silicon-carbon material.

[0074] Comparative Example 2: A method for preparing a silver fluoride composite silicon-carbon material, which differs from Example 1 in that, in step S1, silver nitrate crystals are added to anhydrous ethanol and ultrasonically dispersed to obtain a silver nitrate suspension, and the silicon-carbon suspension and the silver nitrate suspension are mixed at a mass ratio of 1:0.6.

[0075] Structural characterization: The silver fluoride composite silicon-carbon material prepared in Example 1 was characterized by SEM as follows: Figure 2 As shown, from Figure 2 As can be seen, silver fluoride nanoparticles and graphitic carbon nitride form a continuous and dense composite coating layer on the surface of silicon-carbon matrix. Its microstructure is relatively rough and has flexible buffering properties, which can effectively anchor the silicon-carbon matrix and alleviate the volume expansion of silicon, thereby improving the stability and electrochemical performance of the electrode structure.

[0076] Performance testing: The silicon-carbon matrix prepared in Preparation Example 1 was used as a blank example. The silicon-carbon materials in the blank example, Examples 1 to 7, and Comparative Examples 1 to 2 were used as active materials. They were mixed with binder (LA136D) and conductive agent (Super P) in a ratio of 8:1:1 to prepare active slurries. The active slurries were coated on copper current collectors, vacuum dried, and rolled into composite sheets. Lithium metal was used as the counter electrode, lithium hexafluorophosphate as the electrolyte, and polypropylene microporous membrane as the separator. The cells were assembled into coin cells in a glove box. After activation at a current density of 0.05C for three cycles, the cells were cycled at a current density of 0.5C at room temperature for 200 cycles. The initial reversible specific capacity, initial coulombic efficiency, and capacity retention rate after 200 cycles were calculated. The results are shown in Table 1 below.

[0077] Table 1 Electrochemical performance test data of coin cells

[0078] Based on Examples 1 to 3, Table 1 shows that short-term graphitization followed by surface silane treatment of the silicon-carbon matrix helps improve the structural stability of the silicon-carbon matrix during battery cycling. It also improves the uniformity of the loading of the silver fluoride buffer layer on the surface of the silicon-carbon matrix, thereby synergistically improving the capacity retention of the silicon-carbon material during long cycles. Examples 1 and 4 show that coating the surface of commercially available silicon-carbon materials with a silver fluoride buffer layer can also effectively improve electrochemical performance. Examples 1 and 5 show that using urea as a carbon source and forming a g-C3N4 buffer layer on the surface of the silicon-carbon matrix helps improve the cycling stability of the silicon-carbon material. Examples 1, Comparative Examples 1 and 2 show that fluorination of the nano-silver in the buffer layer helps improve cycling stability, and the surface-coated carbon layer / g-C3N4 layer helps improve cycling stability and the loading of silver fluoride nanoparticles.

[0079] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preparing a silver fluoride composite silicon-carbon material, characterized in that, include: The composite precursor is obtained by mixing silicon-carbon matrix, silver source and carbon source in a liquid environment and then evaporating the solvent. The composite precursor is heat-treated in an inert atmosphere at 400℃-600℃ to obtain a composite intermediate; the composite intermediate is fluorinated to obtain silver fluoride composite silicon-carbon material.

2. The preparation method according to claim 1, characterized in that: The silver source includes one of silver acetate, silver nitrate, silver oxide, silver chloride, and silver sulfate; and / or, the carbon source includes one of citric acid, glucose, urea, and phenolic resin; and / or, the liquid environment includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, dichloromethane, and N,N-dimethylacetamide.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the silver source to the carbon source is 8:(5-7); and / or, the mass concentration of the silver source in the liquid environment is 0.3%-1.5%; and / or, the mass concentration of the silicon-carbon matrix in the liquid environment is 5%-15%; and / or, the solvent is evaporated at 50℃-80℃; and / or, the composite precursor is obtained after evaporating the solvent and drying.

4. The preparation method according to claim 1, characterized in that: The liquid environment contains a dispersant; wherein the concentration of the dispersant in the liquid environment is 1wt%-10wt%; and / or, the dispersant includes one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol; and / or, after the dispersant is stirred and dissolved in the liquid environment, a silicon-carbon matrix, a silver source, and a carbon source are added and ultrasonically mixed.

5. The preparation method according to claim 1, characterized in that: The composite precursor is heated at a rate of 1℃ / min to 20℃ / min; and / or, heat-treated for 1h to 3h; and / or, the inert atmosphere includes either argon or nitrogen; and / or, the flow rate of the inert atmosphere is 1L / min to 20L / min; and / or, the pressure of the inert atmosphere is 0.1MPa to 1MPa.

6. The preparation method according to claim 1, characterized in that: The composite intermediate is mixed with a fluorine source and then fluorinated at high temperature in a protective atmosphere at 200℃-400℃ to obtain silver fluoride composite silicon-carbon material; wherein: the fluorine source includes at least one of ammonium hydrogen fluoride, trifluoroacetic acid, and ammonium fluoride; and / or, the mass ratio of the composite intermediate to the fluorine source is 1:(0.01-0.15); and / or, the high-temperature fluorination is carried out for 2h-4h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The method for preparing the silicon-carbon matrix includes: depositing nano-silicon within a porous carbon framework to obtain a silicon-carbon precursor; graphitizing the silicon-carbon precursor at 1200℃-1400℃ for 1 min-5 min to obtain a silicon-carbon intermediate; and surface modifying the silicon-carbon intermediate to obtain a silicon-carbon matrix; wherein the porous carbon framework includes a porous carbon framework doped with heterogeneous elements or undoped.

8. The preparation method according to claim 7, characterized in that: The porous carbon framework has a pore size of 1 nm to 100 nm; and / or, the heteroelement includes one of nitrogen, sulfur, boron, phosphorus, and fluorine; and / or, the porous carbon framework is subjected to chemical vapor deposition in a silicon source gas; and / or, the silicon-carbon intermediate is subjected to surface silane treatment to obtain a silicon-carbon matrix.

9. A silver fluoride composite silicon-carbon material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It includes a silicon-carbon matrix and a composite buffer layer formed on the surface of the silicon-carbon matrix, wherein the composite buffer layer includes a carbon-based coating layer and nano-silver fluoride particles doped in the carbon-based coating layer.

10. The application of a silver fluoride composite silicon-carbon material prepared by any one of claims 1 to 8 in a lithium battery.

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