Silicon-carbon negative electrode material, preparation method thereof and automobile

Abstract

The embodiment of the invention provides a silicon-carbon negative electrode material, a preparation method thereof and an automobile, and belongs to the field of lithium ion battery negative electrode materials. The preparation method comprises the following steps: mixing porous carbon with silicone oil to obtain a first mixture; sequentially carrying out stirring and ultrasonic treatment on the first mixture to obtain a precursor material; mixing the precursor material with molten salt and a reducing agent, and reacting to obtain a second mixture; and sequentially washing, drying and grinding the second mixture to obtain the silicon-carbon negative electrode material. The preparation method provided by the invention has the characteristics of simple process flow, low cost, high safety and high production efficiency.

Description

Silicon-carbon anode materials and their preparation methods in automobiles Technical Field

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

[0002] The anode material has a significant impact on the energy density and cycle performance of lithium-ion batteries. Graphite, with its excellent conductivity, is the most common anode material, but its specific capacity is low, only 372 mAh / g, limiting the performance of the resulting lithium-ion batteries. Silicon, on the other hand, has a theoretical specific capacity of 4200 mAh / g. By combining graphite and silicon to prepare silicon-carbon anode materials, the specific capacity of the anode material can be improved, thereby increasing the energy density of lithium-ion batteries. However, silicon-carbon anode materials suffer from volume expansion during the charge and discharge process of lithium-ion batteries. Specifically, lithium-ion insertion into silicon significantly increases the volume of the silicon material, while lithium-ion extraction causes a significant shrinkage. This volume change leads to structural instability in the silicon-carbon anode material, affecting the cycle performance of lithium-ion batteries. Furthermore, the volume expansion of silicon also increases the internal pressure of the battery, posing a safety hazard to lithium-ion batteries.

[0003] In existing technologies, some researchers prepare silicon-carbon anode materials using chemical vapor deposition (CVD). This method involves introducing silane gas into a porous carbon framework to react and obtain a silicon-carbon precursor containing nano-silicon. Then, an organic gas is introduced for surface carbonization, allowing the nano-silicon to be stably distributed within the pores of the porous carbon framework. Silicon-carbon anode materials prepared using this method exhibit the property of suppressing the volume expansion of silicon materials. However, silane is flammable and explosive, posing significant safety hazards to this method. Furthermore, CVD has low production efficiency and high preparation costs, making large-scale production difficult.

[0004] There is currently no good solution to the above problems. Summary of the Invention

[0005] This application provides a silicon-carbon anode material, its preparation method, and an automobile, to at least solve the problem of volume expansion in existing silicon-carbon anode materials, as well as the technical problems of significant safety hazards, low production efficiency, and high preparation cost associated with CVD preparation of silicon-carbon anode materials.

[0006] According to one aspect of the embodiments of this application, a method for preparing a silicon-carbon anode material is provided, comprising:

[0007] Porous carbon is mixed with silicone oil to obtain the first mixture;

[0008] The first mixture was sequentially stirred and ultrasonicated to obtain the precursor material;

[0009] The precursor material is mixed with molten salt and reducing agent, and reacted to obtain a second mixture;

[0010] The second mixture was washed, dried and ground in sequence to obtain silicon-carbon anode material.

[0011] Furthermore, the mass ratio of porous carbon to silicone oil is 1:(0.5~5).

[0012] Furthermore, the silicone oil is selected from at least one of methyl silicone oil, ethyl silicone oil, and phenyl silicone oil. Preferably, the silicone oil is methyl silicone oil.

[0013] Furthermore, the number-average molecular weight of the silicone oil is 3780 g / mol to 9430 g / mol.

[0014] Furthermore, the viscosity of the silicone oil is 50 mPa·s to 200 mPa·s.

[0015] Furthermore, the pore volume of the porous carbon is 0.116 mL / g to 0.287 mL / g.

[0016] Furthermore, the average pore size of the porous carbon is 10 nm to 40 nm.

[0017] Furthermore, the specific surface area of ​​porous carbon is 168 m². 2 / g~369m 2 / g.

[0018] Furthermore, the temperature for ultrasonic treatment is 20℃~40℃.

[0019] Furthermore, the ultrasonic treatment time is 0.5h to 2h.

[0020] Furthermore, the mass ratio of the precursor material, molten salt, and reducing agent is 1:(5~30):(1~5).

[0021] Furthermore, the molten salt is a metal chloride. Preferably, the metal chloride is selected from at least one of aluminum trichloride, ferric trichloride, magnesium chloride, calcium chloride, and zinc chloride.

[0022] Furthermore, the reducing agent is a metal hydride. Preferably, the metal hydride is selected from at least one of calcium hydride and sodium hydride.

[0023] Furthermore, the reaction temperature is 200℃~400℃.

[0024] Furthermore, the reaction time is 1 to 5 hours.

[0025] Furthermore, the reaction is carried out in nitrogen and / or an inert gas. Preferably, the inert gas is selected from at least one of helium and argon.

[0026] Furthermore, the steps of washing and drying the second mixture sequentially satisfy the following: the second mixture is washed with distilled water and / or ethanol.

[0027] Furthermore, the steps of washing and drying the second mixture sequentially satisfy the following condition: the number of washing cycles is 2 to 4.

[0028] Furthermore, the steps of washing and drying the second mixture sequentially satisfy the condition that the drying is vacuum drying.

[0029] Furthermore, the steps of washing and drying the second mixture sequentially satisfy the following: the drying temperature is 60℃~120℃.

[0030] Furthermore, the steps of washing and drying the second mixture sequentially satisfy the following: the drying time is 8h~16h.

[0031] Furthermore, after grinding the dried material, the preparation method of silicon-carbon anode material also includes: mixing the ground material with a carbon source to obtain a mixed material, and calcining the mixed material in an inert atmosphere to obtain silicon-carbon anode material.

[0032] Preferably, the calcination temperature is 500℃~900℃.

[0033] Preferably, the calcination time is 2h to 4h.

[0034] Preferably, the carbon source is 1-butyl-3-methylimidazolium acetate.

[0035] According to another aspect of the embodiments of this application, a silicon-carbon anode material is also provided, which is prepared according to any of the preparation methods of silicon-carbon anode materials in the foregoing technical solutions.

[0036] According to another aspect of the embodiments of this application, a car is also provided, the car including a battery, the battery including the silicon-carbon anode material of the aforementioned solution.

[0037] In this embodiment, utilizing the fluidity of silicone oil, a stirring and ultrasonic treatment method is used to fill the pores of porous carbon with silicone oil to obtain a precursor material. Subsequently, the silicone oil in the precursor material is reduced in situ to nanoscale silicon particles (nano-silicon) under a molten salt reduction system. After a series of post-processing steps such as washing, drying, and grinding, a silicon-carbon anode material is obtained. The nano-silicon obtained from the in-situ reduction is distributed within the pore structure of the porous carbon, giving the porous carbon a confinement effect on the nano-silicon, which helps to suppress the volume expansion of the silicon material, thereby improving the cycle performance and safety of the lithium-ion battery. The preparation method provided in this application has the characteristics of simple process flow, low cost, high safety, and high production efficiency, possessing the potential for industrial production. It solves the problem of volume expansion in existing silicon-carbon anode materials, as well as the significant safety hazards, low production efficiency, and high preparation cost associated with CVD preparation methods for silicon-carbon anode materials. Attached Figure Description

[0038] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0039] Figure 1 is a flowchart of the preparation method of the silicon-carbon anode material provided by the present invention;

[0040] Figure 2 is a first charge-discharge curve of the silicon-carbon anode material provided in Example 9;

[0041] Figure 3 is a cycle performance curve of the silicon-carbon anode material provided in Example 9 after 100 cycles at a current density of 0.1 A / g;

[0042] Figure 4 is a cycle performance curve of the silicon-carbon anode material provided in Example 9 after 2500 cycles at a current density of 2A / g. Detailed Implementation

[0043] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0044] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0045] As described in the background section, existing silicon-carbon anode materials suffer from volume expansion, and the CVD preparation method for silicon-carbon anode materials presents significant safety hazards, low production efficiency, and high preparation costs. To address these technical problems, this application provides a typical embodiment of a method for preparing silicon-carbon anode materials, as shown in Figure 1, comprising:

[0046] S1. Mix porous carbon with silicone oil to obtain a first mixture;

[0047] S2. The first mixture is stirred and ultrasonically treated sequentially to obtain the precursor material;

[0048] S3. The precursor material is mixed with molten salt and reducing agent, and the mixture is reacted to obtain a second mixture;

[0049] S4. The second mixture is washed, dried and ground in sequence to obtain silicon-carbon anode material.

[0050] In this invention, the fluidity of silicone oil is utilized to fill the pores of porous carbon with silicone oil through stirring and ultrasonic treatment, yielding a precursor material. Subsequently, the silicone oil in the precursor material is reduced in situ to nanoscale silicon particles (nano-silicon) under a molten salt reduction system. After a series of post-processing steps including washing, drying, and grinding, a silicon-carbon anode material is obtained. The nano-silicon is distributed within the pore structure of the porous carbon, giving the porous carbon a confining effect on the nano-silicon, which helps suppress the volume expansion of the silicon material, thereby improving the cycle performance and safety of the lithium-ion battery.

[0051] In the above preparation method, silicone oil is not only highly safe but also inexpensive; the molten salt reduction system composed of molten salt and reducing agent has the characteristic of in-situ reduction, which can directly reduce the silicone oil in the pores of porous carbon to nano-silicon, thereby using the porous carbon framework to suppress the volume expansion of silicon materials; the molten salt reduction system is suitable for liquid phase reduction and has a low reduction temperature, which helps to reduce the difficulty of preparing silicon-carbon anode materials; in addition, the above preparation process does not require expensive equipment or instruments and the process is short, thus it has the characteristics of simple process, low cost, high safety and high production efficiency, and has the potential for industrial production.

[0052] In some embodiments, the mass ratio of porous carbon to silicone oil is 1:(0.5~5). Typical, but not limiting, mass ratios of porous carbon to silicone oil are 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or any range of two such values. Preferably, the mass ratio of porous carbon to silicone oil is 1:(1~2).

[0053] In the above embodiments of this application, by limiting the mass ratio of porous carbon to silicone oil, the reduction effect can be improved, and the silicon-carbon ratio in the silicon-carbon anode material can be effectively controlled, thereby balancing the conductivity and specific capacity of the silicon-carbon anode material. Furthermore, the distribution state and size of nano-silicon in the porous carbon framework can be controlled, thereby regulating the microstructure of the silicon-carbon anode material. By controlling the conductivity, specific capacity, and microstructure of the silicon-carbon anode material, the cycle performance of lithium-ion batteries can be further improved.

[0054] In some embodiments, the silicone oil is selected from at least one of methyl silicone oil, ethyl silicone oil, and phenyl silicone oil. Preferably, the silicone oil is methyl silicone oil. More preferably, the silicone oil is dimethyl silicone oil.

[0055] In the above embodiments of this application, by limiting the type of silicone oil, it is helpful to utilize its fluidity and chemical stability to efficiently penetrate into the pores of porous carbon. In addition, the silicone oil is easily reduced in the molten salt reduction system, and thus can be fully and efficiently reduced to nano-silicon.

[0056] In some embodiments, the number-average molecular weight of the silicone oil is 3780 g / mol to 9430 g / mol.

[0057] Number-average molecular weight primarily reflects the average length of polymer chains and significantly affects the viscosity, surface tension, and stability of silicone oil. In the embodiments described above, limiting the number-average molecular weight to the aforementioned range helps improve the permeability of silicone oil to porous carbon, promotes the uniform distribution of silicone oil within the pores of porous carbon, and thus enhances the stability of the silicon-carbon anode material's performance. Furthermore, silicone oil within the aforementioned range is relatively stable and less volatile, which helps improve reaction efficiency and reaction stability.

[0058] In some implementations, the viscosity of the silicone oil is 50 mPa·s to 200 mPa·s.

[0059] Viscosity refers to the internal friction of a liquid, mainly reflecting the ease or difficulty of liquid flow. It is determined by multiple factors, including number-average molecular weight, molecular weight distribution, degree of branching, and degree of crosslinking. In the embodiments described above, limiting the viscosity of the silicone oil to the aforementioned range helps to control its flowability and permeability, making it easier for the silicone oil to enter the porous carbon pores.

[0060] By limiting the number-average molecular weight and viscosity of the silicone oil to the above range, the silicon content in the silicone oil can also be controlled within a suitable range, thereby effectively improving the specific capacity of silicon-carbon anode materials.

[0061] In some embodiments, the pore volume of the porous carbon is 0.116 mL / g to 0.287 mL / g.

[0062] The pore volume of porous carbon refers to the total volume of all pores in a unit mass of porous carbon. In the above embodiments of this application, by limiting the pore volume of porous carbon within the above range, it is helpful to control the volume of silicone oil entering the pores of porous carbon. On the one hand, this helps to balance the conductivity and specific capacity of silicon-carbon anode materials, and on the other hand, it helps to use the porous carbon framework to suppress the volume expansion of silicon materials and improve cycle performance.

[0063] In some embodiments, the average pore size of the porous carbon is 10 nm to 40 nm.

[0064] In the above embodiments of this application, by limiting the pore size of the porous carbon, it is helpful to promote the rapid entry of silicone oil into the interior of the porous carbon, while ensuring the stability of the porous carbon framework.

[0065] In some embodiments, the specific surface area of ​​porous carbon is 168 m². 2 / g~369m 2 / g.

[0066] In the above embodiments of this application, limiting the specific surface area of ​​porous carbon to the above range helps to increase the contact area between silicone oil and porous carbon, ensuring that silicone oil can penetrate and fill the pores of porous carbon more effectively; on the other hand, it helps to increase the reaction area, ensuring that silicone oil is fully reduced to nano-silicon.

[0067] Simultaneously controlling the pore volume, average pore size, and specific surface area of ​​porous carbon within the aforementioned range helps to promote the penetration of silicone oil into the porous carbon framework before its reduction, allowing the reduced nano-silicon to embed into the pores of the porous carbon, thereby effectively suppressing the volume expansion of silicon materials and improving the cycle performance of silicon-carbon anode materials.

[0068] In some implementations, the stirring time is 10 min to 60 min.

[0069] In the above embodiments of this application, the stirring time has no significant effect on the prepared silicon-carbon anode material. It is sufficient to stir the porous carbon and silicone oil to fully disperse and uniformly mix them.

[0070] In some embodiments, the temperature of ultrasonic treatment is 20°C to 40°C.

[0071] In the above embodiments of this application, ultrasonic treatment helps to uniformly disperse and mix silicone oil and porous carbon. By limiting the temperature of ultrasonic treatment within the above range, it helps to promote the uniform penetration of silicone oil into porous carbon, while ensuring the stability of silicone oil during the dispersion and penetration process.

[0072] In some implementations, the ultrasonic treatment time is 0.5h to 2h.

[0073] In the above embodiments of this application, limiting the ultrasonic treatment time within the above range helps to ensure that the silicone oil is fully filled into the pores of the porous carbon, while saving process time, reducing energy consumption, and improving process efficiency.

[0074] In some embodiments, the mass ratio of the precursor material, molten salt and reducing agent is 1:(5~30):(1~5).

[0075] In the above embodiments of this application, a molten reduction system is constructed using molten salt and a reducing agent to reduce the silicone oil in the precursor material to elemental silicon. By limiting the mass ratio of the precursor material, molten salt, and reducing agent to the above range, it is helpful to fully reduce the silicone oil in the precursor material, thereby obtaining a silicon-carbon composite structure.

[0076] In some embodiments, the molten salt is a metal chloride. Preferably, the metal chloride is selected from at least one of aluminum trichloride, ferric trichloride, magnesium chloride, calcium chloride, and zinc chloride.

[0077] In the embodiments described above, a suitable molten salt not only provides a stable high-temperature environment for the reaction but also simultaneously regulates the pH and redox potential of the reaction system, thereby helping to improve the reaction rate and selectivity. Limiting the type of molten salt to the above range ensures that the molten salt remains stable at high temperatures and can efficiently and selectively reduce the silicone oil in the precursor material to elemental silicon, thereby improving the silicon-carbon composite structure.

[0078] In some embodiments, the reducing agent is a metal hydride. Preferably, the metal hydride is selected from at least one of calcium hydride and sodium hydride. More preferably, the metal hydride is calcium hydride.

[0079] In the embodiments described above in this application, limiting the reducing agent to a metal hydride with strong reducing properties helps to fully and efficiently reduce silicone oil to elemental silicon. Among them, calcium hydride has the best reduction effect, which not only helps to improve the microstructure of silicon-carbon anode materials and enhance their electrochemical performance, but also has good safety.

[0080] In some embodiments, the reaction temperature is 200°C to 400°C.

[0081] In the above embodiments of this application, by limiting the reaction temperature within the above range, it helps to provide sufficient energy for the reaction to improve reaction efficiency; on the other hand, it helps to improve reaction selectivity and reduce the occurrence of side reactions.

[0082] In some implementations, the reaction time is 1 hour to 5 hours.

[0083] In the above embodiments of this application, by limiting the reaction time within the above range, it helps to provide sufficient time for the reaction so that the silicone oil in the precursor material can be fully reduced to elemental silicon.

[0084] In some embodiments, the reaction is carried out in nitrogen and / or an inert gas. Preferably, the inert gas is selected from at least one of helium and argon.

[0085] In the above embodiments of this application, limiting the reaction conditions can effectively isolate air, reduce the probability of side reactions, and help to stabilize and control the reaction temperature and pressure within a suitable range, thereby improving reaction efficiency and reaction stability.

[0086] In some embodiments, the steps of washing and drying the second mixture sequentially satisfy the following: the second mixture is washed with distilled water and / or ethanol.

[0087] In the above embodiments of this application, washing with distilled water or ethanol can remove impurities from the second mixture, resulting in a silicon-carbon anode material with high purity.

[0088] In some embodiments, the steps of washing and drying the second mixture sequentially satisfy the following: the number of washing cycles is 2 to 4. Preferably, the washing time for each cycle is 3 to 5 hours.

[0089] In the above embodiments of this application, thorough washing helps to remove impurities, thereby further improving purity and enhancing the performance of silicon-carbon anode materials.

[0090] In some embodiments, the steps of washing and drying the second mixture sequentially satisfy the condition that the drying is vacuum drying.

[0091] In the above embodiments of this application, vacuum drying can isolate oxygen and remove moisture rapidly at a relatively low temperature, so that the structure of the second mixture remains stable during the drying process.

[0092] In some embodiments, the steps of washing and drying the second mixture sequentially satisfy the following: the drying temperature is 60°C to 120°C.

[0093] In the above embodiments of this application, limiting the drying temperature to the above range helps to quickly remove moisture from the second mixture while reducing energy consumption.

[0094] In some embodiments, the steps of washing and drying the second mixture sequentially satisfy the following: the drying time is 8h to 16h.

[0095] In the above embodiments of this application, limiting the drying time to the above range helps to reduce energy consumption and shorten process time while ensuring sufficient drying.

[0096] In some embodiments, after grinding the dried material, the preparation method of the silicon-carbon anode material further includes: mixing the ground material with a carbon source to obtain a mixed material, and calcining the mixed material in nitrogen and / or an inert gas to obtain the silicon-carbon anode material. Preferably, the calcination temperature is 500℃~900℃. Preferably, the calcination time is 2h~4h. Preferably, the carbon source is 1-butyl-3-methylimidazolium acetate. Preferably, the inert gas is selected from at least one of helium and argon.

[0097] In the above embodiments of this application, the material obtained from grinding is mixed with a carbon source and then calcined to coat the surface of the ground material with a carbon layer. This method helps to reduce the exposed area of ​​nano-silicon and form a denser silicon-carbon composite structure, thereby enhancing the suppression of silicon volume expansion. Furthermore, carbon coating also helps to strengthen the conductive structure of the silicon-carbon anode material, thereby improving the rate performance of lithium-ion batteries. 1-Butyl-3-methylimidazolium acetate is an ionic liquid with good stability and fluidity at room temperature. It can uniformly coat the surface of the ground material without the need for additional solvents, and then be stably carbonized at high temperatures to form a uniform carbon coating layer. In addition, 1-Butyl-3-methylimidazolium acetate has low volatility and toxicity, making the coating process more controllable. The imidazole in the 1-Butyl-3-methylimidazolium acetate molecule can be converted into nitrogen dopant in the silicon-carbon anode material during carbonization, enhancing the material's structural stability and improving electron transport efficiency.

[0098] In some embodiments, the preparation method of silicon-carbon anode material further includes: first cooling the second mixture to 20°C~40°C, then washing and drying the second mixture in sequence, and then grinding the dried material to obtain silicon-carbon anode material.

[0099] In the above embodiments of this application, the purpose of grinding the dried material is to break down the large particles formed by agglomeration in the second mixture into smaller particles, thereby obtaining a silicon-carbon anode material with uniform particle size.

[0100] In another typical embodiment of the present invention, a silicon-carbon anode material is provided, which is prepared according to any of the preparation methods for silicon-carbon anode materials described in the foregoing technical solutions. Specifically, the silicon-carbon anode material has a porous carbon framework, in which nano-silicon is distributed within the pore structure of the porous carbon framework.

[0101] In the above embodiments of this application, nano-silicon is embedded in a porous carbon framework and forms a composite structure therewith. On the one hand, nano-silicon helps to improve the specific capacity of silicon-carbon anode materials; on the other hand, porous carbon helps to improve the conductivity of silicon-carbon anode materials, while also limiting the volume expansion of nano-silicon.

[0102] In yet another typical embodiment of the present invention, an automobile is provided, the automobile including a battery, the battery including the silicon-carbon anode material of the aforementioned scheme.

[0103] In the above embodiments of this application, the composite structure of the aforementioned silicon-carbon anode material helps to improve the energy density, cycle stability, and safety of the battery, thereby improving the range and safety of the vehicle.

[0104] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0105] Some of the materials used in the examples and comparative examples are as follows:

[0106] Porous carbon-1: pore volume is 0.116 mL / g, average pore size is 20 nm, and specific surface area is 227 m². 2 / g, purchased from Green Bamboo Charcoal Co., Ltd.

[0107] Porous carbon-2: pore volume is 0.051 mL / g, average pore size is 5 nm, and specific surface area is 100 m². 2 / g, homemade rice husk activated carbon.

[0108] Porous carbon-3: pore volume is 0.225 mL / g, average pore size is 10 nm, and specific surface area is 168 m². 2 / g, purchased from Tianbang New Materials.

[0109] Porous carbon-4: pore volume is 0.287 mL / g, average pore size is 40 nm, and specific surface area is 369 m². 2 / g, purchased from Tianbang New Materials.

[0110] Dimethyl silicone oil-1: 201-100 is a dimethyl silicone oil with a number average molecular weight of 5970 g / mol and a viscosity of 100 mPa·s, purchased from Dow Corning.

[0111] Dimethyl silicone oil-2: 201-10 dimethyl silicone oil, with a number average molecular weight of 700 g / mol and a viscosity of 10 mPa·s, was purchased from Dow Corning.

[0112] Dimethyl silicone oil-3: 201-50 dimethyl silicone oil, with a number average molecular weight of 3780 g / mol and a viscosity of 50 mPa·s, was purchased from Dow Corning.

[0113] Dimethyl silicone oil-4: 201-200 dimethyl silicone oil, with a number average molecular weight of 9430 g / mol and a viscosity of 200 mPa·s, purchased from Dow Corning.

[0114] Sodium hydride: Product number S817935, purchased from Maclean's.

[0115] Example 1

[0116] This embodiment provides a method for preparing a silicon-carbon anode material, the preparation steps of which include:

[0117] S1. Porous carbon-1 and dimethyl silicone oil-1 are mixed at a mass ratio of 1:1.5 to obtain the first mixture.

[0118] S2. Stir the first mixture for 20 minutes, then sonicate it at 30°C for 1 hour to obtain the precursor material.

[0119] S3. The precursor material is mixed with aluminum trichloride (molten salt) and calcium hydride (reducing agent) in a mass ratio of 1:10:2 and reacted at 250°C in a nitrogen atmosphere for 2.5 h. The aluminum trichloride and calcium hydride form a molten salt reduction system. During the reaction, the silicone oil in the precursor material can be reduced to elemental silicon using the molten salt reduction system to obtain the second mixture.

[0120] S4. Wash the second mixture three times with distilled water, each time for 4 hours. Then place the washed product in a vacuum environment at 60°C for 16 hours to obtain the dried material. Finally, grind the dried material for 30 minutes to obtain the silicon-carbon anode material.

[0121] This embodiment also provides a silicon-carbon anode material, which is prepared by the method provided in this embodiment. The silicon-carbon anode material has a porous carbon framework, and nano-silicon is distributed in the pore structure of the porous carbon framework.

[0122] Examples 2-5

[0123] Examples 2-5 provide a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that the mass ratio of porous carbon-1 to dimethyl silicone oil-1 is 1:0.5 (Example 2), 1:1 (Example 3), 1:2 (Example 4), and 1:5 (Example 5), respectively.

[0124] Example 6

[0125] Example 6 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that the reducing agent is sodium hydride.

[0126] Comparative Example 1

[0127] Comparative Example 1 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that molten salt is not used in step S3. Specifically, in step S3, the precursor material and calcium hydride (reducing agent) are mixed at a mass ratio of 1:2 and reacted at 250°C in a nitrogen atmosphere for 2.5 hours. The reducing agent is used to reduce the silicone oil in the precursor material to elemental silicon, resulting in a second mixture.

[0128] Example 7

[0129] Example 7 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that dimethyl silicone oil-1 in step S1 is replaced with dimethyl silicone oil-2.

[0130] Example 8

[0131] Example 8 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that porous carbon-1 in step S1 is replaced with porous carbon-2.

[0132] Example 9

[0133] Example 9 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that step S4 further includes carbon coating of the ground material, with 1-butyl-3-methylimidazolium acetate as the carbon source. Specifically, in step S4, after grinding the dried material for 30 minutes, the ground material is mixed with 1-butyl-3-methylimidazolium acetate to obtain a mixed material. The mixed material is then calcined in nitrogen at 800°C for 3 hours to obtain the silicon-carbon anode material.

[0134] Example 10

[0135] Example 10 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and that of Example 1 is that step S4 further includes carbon coating of the ground material, with microcrystalline cellulose (MCC) as the carbon source. Specifically, in step S4, the dried material is ground for 30 minutes, and then the ground material is mixed with MCC to obtain a mixed material. The mixed material is then calcined in nitrogen at 800°C for 3 hours to obtain the silicon-carbon anode material.

[0136] Example 11

[0137] Example 11 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that the preparation steps include:

[0138] S1. Porous carbon-3 and dimethyl silicone oil-3 are mixed at a mass ratio of 1:1.5 to obtain the first mixture.

[0139] S2. Stir the first mixture for 10 min, then sonicate it at 40°C for 0.5 h to obtain the precursor material.

[0140] S3. The precursor material is mixed with ferric chloride (molten salt) and calcium hydride (reducing agent) in a mass ratio of 1:5:1 and reacted at 200°C in an argon atmosphere for 5 hours. Ferric chloride and calcium hydride form a molten salt reduction system. During the reaction, the silicone oil in the precursor material can be reduced to elemental silicon using the molten salt reduction system to obtain the second mixture.

[0141] S4. Wash the second mixture four times with ethanol for 3 hours each time. Then place the washed product in a vacuum environment at 90°C for 12 hours to obtain the dried material. Finally, grind the dried material for 40 minutes to obtain the silicon-carbon anode material.

[0142] This embodiment also provides a silicon-carbon anode material, which is prepared by the method provided in this embodiment. The silicon-carbon anode material has a porous carbon framework, and nano-silicon is distributed in the pore structure of the porous carbon framework.

[0143] Example 12

[0144] Example 12 provides a method for preparing a silicon-carbon anode material and the silicon-carbon anode material obtained by the aforementioned method. The difference between the preparation method and Example 1 is that the preparation steps include:

[0145] S1. Porous carbon-4 and dimethyl silicone oil-4 are mixed at a mass ratio of 1:1.5 to obtain the first mixture.

[0146] S2. Stir the first mixture for 60 min, then sonicate it at 20°C for 2 h to obtain the precursor material.

[0147] S3. Mix the precursor material with magnesium chloride (molten salt) and calcium hydride (reducing agent) at a mass ratio of 1:30:5, and react at 400°C in a helium atmosphere for 1 hour. Magnesium chloride and calcium hydride form a molten salt reduction system. During the reaction, the silicone oil in the precursor material can be reduced to elemental silicon using the molten salt reduction system to obtain the second mixture.

[0148] S4. Wash the second mixture twice with distilled water, each time for 5 hours. Then place the washed product in a vacuum environment at 120°C for 8 hours to obtain the dried material. Finally, grind the dried material for 20 minutes to obtain the silicon-carbon anode material.

[0149] This embodiment also provides a silicon-carbon anode material, which is prepared by the method provided in this embodiment. The silicon-carbon anode material has a porous carbon framework, and nano-silicon is distributed in the pore structure of the porous carbon framework.

[0150] Comparative Example 2

[0151] Comparative Example 2 provides a method for preparing a silicon-carbon anode material. The difference from Example 1 is that the silicon-carbon anode material is prepared by chemical vapor deposition.

[0152] The cost comparison between Example 1 and Comparative Example 2 is shown in Table 1.

[0153]

[0154] Performance testing

[0155] The rate performance and cycle performance of the silicon-carbon anode materials provided in Examples 1-12 and Comparative Example 1 were tested respectively.

[0156] The performance testing method is as follows:

[0157] Button-type half-cells were prepared using the silicon-carbon anode materials provided in Examples 1-12 and Comparative Example 1, respectively. The preparation method included: uniformly mixing sodium alginate binder, acetylene black, and silicon-carbon anode material at a mass ratio of 1:1:3 to obtain a negative electrode slurry; then uniformly coating the negative electrode slurry onto the surface of a copper foil using a coater; and finally drying the copper foil coated with the negative electrode slurry in a vacuum drying oven to obtain a negative electrode sheet. The negative electrode sheet was then cut and set aside. The compaction density of the negative electrode sheet was 1.4 g / cm³. 3 Next, LB315 electrolyte was dropped onto the surfaces of the negative electrode and the spring sheet under a dry, inert atmosphere. Then, the negative electrode, two separators, lithium sheet, and spring sheet were assembled to obtain a button-type half-cell.

[0158] The method for measuring the compaction density of the negative electrode sheet is as follows: weigh the negative electrode sheet with a balance, then immerse the negative electrode sheet in water and measure the water level change to obtain the volume of the negative electrode sheet. Finally, divide the mass of the negative electrode sheet by the volume of the negative electrode sheet to obtain the compaction density.

[0159] (1) Test the first discharge specific capacity and the first charge-discharge efficiency.

[0160] The initial discharge specific capacity of the prepared button-type half-cell at a current density of 0.1 A / g was tested using a Newway testing system at 25 °C, and the initial coulombic efficiency was calculated. The cell was charged to 3 V at a current density of 0.1 A / g and then discharged to 0.01 V at a current density of 0.1 A / g. The charge and discharge capacity values ​​were recorded, and the initial coulombic efficiency was calculated using the following formula:

[0161] Initial coulombic efficiency (%) = initial discharge capacity / initial charge capacity × 100%.

[0162] (2) Test cycle performance

[0163] The prepared button-type half-cells were subjected to constant current charge-discharge at a constant current of 0.1 A / g. The charging cutoff voltage was 3V, followed by a 10-minute rest period. The discharging cutoff voltage was 0.01V, followed by a 10-minute rest period. This constitutes one cycle. The aforementioned steps were repeated to test the charge-discharge capacity of the button-type half-cells after 5 and 100 cycles at a current density of 0.1 A / g, after 5, 50, and 100 cycles at a current density of 1 A / g, and after 5 and 2500 cycles at a current density of 2 A / g. Then, the discharge capacity retention rate of the battery after n cycles was calculated using the following formula:

[0164] Discharge capacity retention rate (%) = discharge capacity after n cycles / initial discharge capacity × 100%.

[0165] The performance test results are shown in Table 2. The first charge-discharge curve of the silicon-carbon anode material of Example 9 at a current density of 0.1 A / g is shown in Figure 2. The performance curve after 100 cycles at a current density of 0.1 A / g is shown in Figure 3. The performance curve after 2500 cycles at a current density of 2 A / g is shown in Figure 4.

[0166]

[0167] As shown in Figures 2 to 4, and in conjunction with Table 1, this application utilizes the fluidity of silicone oil to fill the pores of porous carbon, and then reduces the silicone oil in situ to nano-silicon under a molten salt reduction system. Finally, the silicon-carbon anode material prepared by a series of post-processing processes has good specific capacity, rate performance and cycle performance, and the silicon-carbon anode material prepared in Example 10 has the best performance.

[0168] Comparing Examples 1-5, Examples 2 and 5 showed relatively low initial discharge specific capacities, and Example 5 exhibited relatively poor cycle performance, indicating that the optimal ratio of porous carbon to silicone oil is 1:(1-2). This is because insufficient silicone oil results in less nano-silicon obtained from the reduction, limiting the performance improvement of the anode material. Excessive silicone oil leads to insufficient contact between the silicone oil and the molten salt and reducing agent, affecting the reduction effect. Furthermore, excessive nano-silicon filling reduces the stability of the anode material structure, thereby affecting cycle performance.

[0169] Compared with Example 1, Example 6 showed relatively poor performance. This is because sodium hydride is highly reactive, making the reaction relatively difficult to control. Furthermore, the commercially available sodium hydride contained paraffin, which hindered the complete reduction reaction. Although the paraffin in sodium hydride can serve as a carbon source, it produces numerous byproducts during high-temperature decomposition and is difficult to decompose into a uniform, high-purity carbon layer, resulting in poor carbon coating and thus limited improvement in the performance of the silicon-carbon anode material.

[0170] The results of Examples 7 and 8 were all worse than those of Example 1, indicating that the choice of porous carbon and silicone oil significantly affects the performance of the prepared silicon-carbon anode material. Specifically, when the number-average molecular weight and viscosity of the silicone oil are low, although the fluidity is good, the silicon content is low, resulting in a limited amount of nano-silicon obtained from the reduction, thus limiting the specific capacity improvement of the silicon-carbon anode material. When the pore volume, average pore size, and specific surface area of ​​the porous carbon are low, more silicone oil cannot enter the pores of the porous carbon but instead deposits on the surface, limiting the effect of the porous carbon in inhibiting volume expansion, thus resulting in relatively poor cycle performance.

[0171] Comparing Examples 9 and 10, it can be seen that 1-butyl-3-methylimidazolium acetate has a better coating effect when used as a carbon source, which helps to further improve the performance of silicon-carbon anode materials.

[0172] In Comparative Example 1, no molten salt was added. Under these conditions, it was not only difficult to break the silicon-oxygen bond, but also to result in insufficient material contact, making it difficult to reduce the silicone oil to elemental silicon. Therefore, the silicon-carbon anode material produced had poor performance.

[0173] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, include: Porous carbon and silicone oil are mixed to obtain a first mixture; the first mixture is then stirred and ultrasonically treated sequentially to obtain a precursor material. The precursor material is mixed with molten salt and reducing agent and reacted to obtain a second mixture; the second mixture is then washed, dried and ground in sequence to obtain the silicon-carbon anode material.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The mass ratio of the porous carbon to the silicone oil is 1:(0.5~5).

3. The method for preparing the silicon-carbon anode material according to claim 1 or 2, characterized in that, The silicone oil is selected from at least one of methyl silicone oil, ethyl silicone oil and phenyl silicone oil; preferably, the silicone oil is methyl silicone oil; and / or, the number average molecular weight of the silicone oil is 3780 g / mol to 9430 g / mol; and / or, the viscosity of the silicone oil is 50 mPa·s to 200 mPa·s.

4. The method for preparing silicon-carbon anode material according to claim 1 or 2, characterized in that, The porous carbon has a pore volume of 0.116 mL / g to 0.287 mL / g; and / or, the average pore size of the porous carbon is 10 nm to 40 nm; and / or, the specific surface area of ​​the porous carbon is 168 m². 2 / g~369m 2 / g.

5. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, The temperature of the ultrasonic treatment is 20℃~40℃; and / or the time of the ultrasonic treatment is 0.5h~2h.

6. The method for preparing the silicon-carbon anode material according to claim 1 or 5, characterized in that, The mass ratio of the precursor material, the molten salt, and the reducing agent is 1:(5~30):(1~5); and / or, the molten salt is a metal chloride; preferably, the metal chloride is selected from at least one of aluminum trichloride, ferric trichloride, magnesium chloride, calcium chloride, and zinc chloride; and / or, the reducing agent is a metal hydride; preferably, the metal hydride is selected from at least one of calcium hydride and sodium hydride; and / or, the reaction temperature is 200℃~400℃; and / or, the reaction time is 1h~5h; and / or, the reaction is carried out in nitrogen and / or an inert gas; preferably, the inert gas is selected from at least one of helium and argon.

7. The method for preparing the silicon-carbon anode material according to claim 6, characterized in that, The washing and drying steps of the second mixture in sequence satisfy at least one of the following conditions: (1) the second mixture is washed with distilled water and / or ethanol; (2) the washing is performed 2 to 4 times; (3) the drying is vacuum drying; (4) the drying temperature is 60°C to 120°C; (5) the drying time is 8h to 16h.

8. The method for preparing silicon-carbon anode material according to claim 1 or 7, characterized in that, After grinding the dried material, the method for preparing the silicon-carbon anode material further includes: mixing the ground material with a carbon source to obtain a mixed material, and calcining the mixed material in an inert atmosphere to obtain the silicon-carbon anode material; preferably, the calcination temperature is 500℃~900℃; and / or, the calcination time is 2h~4h; and / or, the carbon source is 1-butyl-3-methylimidazolium acetate.

9. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material is prepared by the method for preparing silicon-carbon anode materials according to any one of claims 1 to 8.

10. A car, characterized in that, The vehicle includes a battery, the battery including the silicon-carbon anode material as described in claim 9.

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