Preparation methods of carbon-silicon composite materials, carbon-silicon composite materials, negative electrodes and batteries

Abstract

The application discloses a preparation method of carbon-silicon composite material, the carbon-silicon composite material, a negative electrode and a battery. The preparation method comprises the following steps: preparing a hydroxylated nano-silicon material, preparing a gel precursor mixed solution, preparing a gel containing the nano-silicon material, freeze-drying the gel containing the nano-silicon material, calcining and grinding and refining, and obtaining the carbon-silicon composite material. The nano-silicon material is subjected to hydroxylization treatment, the nano-silicon particles with rich hydroxyl groups on the surface generate hydrogen bond action with the gel, the nano-silicon material is added into a precursor solution of the gel and is ultrasonically dispersed, then a crosslinking agent is added to perform crosslinking and curing of the gel, the nano-silicon material can be uniformly distributed in the skeleton of the gel, the contact between the nano-silicon material and the carbon material is enhanced, the electronic conductivity of the nano-silicon is effectively improved, the nano-silicon does not lose the electrical contact by being separated from the carbon material in a plurality of charging and discharging processes, and the electrochemical performance of the battery negative electrode can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a method for preparing a carbon-silicon composite material, the carbon-silicon composite material, a negative electrode, and a battery. Background Technology

[0002] With the booming development of the new energy industry, people have placed higher demands on the energy density of batteries. Currently, the theoretical specific capacity of widely used graphite anodes is 372 mAh / g, which has reached a capacity bottleneck, necessitating the development of anode materials with higher capacity. Silicon, with its theoretical specific capacity of 4200 mAh / g, is considered the most promising next-generation anode material for lithium-ion batteries. However, the severe volume change (up to 300%) of silicon during charge and discharge, the formation of an unstable solid electrolyte interphase (SEI) film, and its poor electronic conductivity hinder its use as a lithium-ion battery anode. Although reducing the size of silicon and preparing nanoscale silicon materials can alleviate the volume expansion problem, it is still insufficient for practical applications.

[0003] To address the above issues, researchers have conducted extensive modification work. Preparing silicon-carbon composites is an effective way to improve the performance of silicon materials as anodes in lithium-ion batteries. However, in conventional silicon-carbon materials, the composite of silicon and carbon substrate is only a simple physical contact; during electrochemical reactions, nano-silicon particles easily detach and lose electrical contact. In the process of modifying silicon materials through silicon-carbon preparation, the small particle size of nano-silicon particles makes them prone to agglomeration, resulting in poor modification effects. While commonly used spray and vapor deposition methods can effectively disperse nano-silicon particles, they are costly.

[0004] Therefore, there is an urgent need to provide a method for preparing carbon-silicon composite materials that can prevent the agglomeration of nano-silicon particles, prevent the shedding of nano-silicon particles during electrochemical reactions, and has a low cost. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a carbon-silicon composite material, a carbon-silicon composite material, a negative electrode, and a battery, which prevents the agglomeration of nano-silicon particles and prevents nano-silicon particles from falling off the carbon material during the electrochemical reaction of charging and discharging, while reducing costs.

[0006] On one hand, the present invention provides a method for preparing a carbon-silicon composite material, comprising:

[0007] The preparation of hydroxylated silicon nanomaterials includes: dispersing silicon nanoparticles in deionized water, adding a hydroxylation reagent, performing ultrasonic dispersion, and hydroxylating the silicon nanoparticles to obtain hydroxylated silicon nanomaterials.

[0008] The preparation of a gel precursor mixed solution includes: dissolving a gel precursor and a crosslinking agent to obtain a gel precursor mixed solution;

[0009] The preparation of a gel containing nano-silicon materials includes: adding hydroxylated nano-silicon materials to a gel precursor mixture solution, heating to a preset temperature to initiate a curing reaction, and obtaining a gel containing nano-silicon materials;

[0010] Freeze-drying a gel containing nano-silicon materials yields a composite nano-silicon particle gel.

[0011] The composite nano-silicon particle gel was calcined and then ground to obtain a carbon-silicon composite material.

[0012] Optionally, the particle size of the nano-silicon particles ranges from 50 nm to 300 nm. If the particle size is too small, severe agglomeration will occur between the silicon particles, resulting in a smaller specific surface area of ​​the material and affecting the electrochemical performance of the material. If the particles are too large, the silicon particles are easily broken and pulverized during charging and discharging, and the electrochemical performance will rapidly decline.

[0013] Optionally, the hydroxylating agent includes at least one of trichlorosilane, trimethoxysilane, ethoxytrimethylsilane, chloromethyltriethoxysilane, ammonia, phytic acid, formaldehyde, methanol, ethanol, sodium hydroxide, and potassium hydroxide.

[0014] Optionally, in the step of preparing hydroxylated silicon nanoparticles, the mass ratio of the hydroxylating agent to the silicon nanoparticles is 1:5 to 1:30. Optional ratios include 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:20, 1:25, or 1:30. A ratio lower than 1:30 will result in fewer hydroxyl groups on the surface of the silicon nanoparticles, leading to insignificant hydroxylation and hindering subsequent bonding between the silicon powder and the gel via hydrogen bonding. A ratio higher than 1:5 will waste the hydroxylating agent. A ratio of 1:5 to 1:30 allows for effective hydroxylation of the silicon nanoparticles; adding excessive hydroxylating agent has little impact on the hydroxylation process and only wastes the agent.

[0015] Optionally, the gel precursor includes at least one of sodium acrylate, acrylamide, vinyl alcohol, methyl methacrylate, and sodium carboxymethyl cellulose;

[0016] The crosslinking agent includes at least one of N,N-thionyldicarboxamide, ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, ethylene oxide, glutaraldehyde, silica, and N,N-methylenebisacrylamide;

[0017] The mass ratio of gel precursor to crosslinking agent is from 100:1 to 1000:1, optionally 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, or 1000:1. Insufficient crosslinking agent will lead to gel preparation failure, as the aqueous solution dissolving the gel precursor will not form a gel-like solid. Excessive crosslinking agent will cause the polymerization reaction of the gel precursor to complete rapidly, resulting in poor gel uniformity and inconsistent local polymerization, leading to variations in gel properties.

[0018] Optionally, dissolving the gel precursor involves adding it to deionized water at a mass ratio of 1:10 to 1:50. Optional ratios include 1:10, 1:20, 1:30, 1:40, or 1:50. Adding too much gel precursor will result in incomplete dissolution, affecting the preparation of a homogeneous gel. Adding too much deionized water will decrease the average concentration of the gel precursor, preventing gel formation.

[0019] Optionally, in the step of preparing a gel containing nano-silicon materials:

[0020] The mass ratio of hydroxylated silicon nanomaterial to gel precursor is 1:2 to 1:20. Optionally, the mass ratio of hydroxylated silicon nanomaterial to gel precursor is 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18, or 1:20. The hydroxylated silicon nanomaterial is added to the gel precursor mixture solution, ultrasonically dispersed until uniform, and heated at 60℃ to 120℃ for 6h to 12h.

[0021] If too few hydroxylated silicon nanoparticles are added (below the minimum value), the specific capacity of the prepared silicon-carbon composite material will be too low, failing to exhibit the high capacity characteristics of silicon-carbon anodes. If too many hydroxylated silicon nanoparticles are added, the gel cannot effectively encapsulate the nanoparticles, leaving too many exposed nanoparticles, or even unloaded onto the gel framework. This fails to improve the electrochemical performance of the silicon nanoparticles, leading to rapid performance degradation of the prepared silicon-carbon anode material.

[0022] Optionally, the gel may include at least one of sodium polyacrylate gel, polyacrylamide gel, polyvinyl alcohol gel, polymethyl methacrylate gel, and sodium carboxymethyl cellulose gel. Optionally, the gel may also be gelatin.

[0023] Optionally, the freeze-drying temperature is -60℃ to -40℃, the freeze-drying pressure is 0.5kPa to 50kPa, and the freeze-drying time is 48h to 72h.

[0024] Freeze-drying temperatures range from -60℃ to -40℃, with selectable options including -60℃, -55℃, -50℃, -45℃, or -40℃. Temperatures below -60℃ slow down the rate at which moisture sublimates directly from a solid to a gaseous state, leading to longer drying cycles and reduced efficiency. Prolonged operation of the freeze dryer, especially below its optimal operating temperature, may increase equipment wear and energy consumption. Temperatures above -40℃ may cause the sample surface to dry too quickly while the interior dries slowly, resulting in uneven drying and affecting product quality.

[0025] The freeze-drying pressure ranges from 0.5 kPa to 50 kPa, with selectable pressures including 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, or 50 kPa. Pressures below 0.5 kPa increase equipment load, requiring the vacuum pump to perform more work to maintain the high vacuum, leading to increased energy consumption and a shortened pump lifespan. At extremely high vacuum levels, gases in the sample may rapidly expand and escape, potentially damaging the product's microstructure. In some cases, excessively high vacuum levels may reduce the drying rate because the rate of water vapor escaping from the product surface may exceed the rate of internal moisture migration to the surface. Pressures above 50 kPa slow the sublimation of moisture from the product, reducing drying efficiency. Moisture in the product may not be effectively removed, resulting in a final product with excessively high moisture content, affecting product stability. If the temperature exceeds the maximum value by too much, the system temperature may approach or exceed the melting point of ice, causing the ice crystals to melt into water, resulting in changes to the sample structure and loss of active ingredients. At lower negative pressures, maintaining a certain drying rate may require increasing the drying chamber temperature, thus increasing energy consumption.

[0026] Freeze-drying time ranges from 48 to 72 hours, with selectable times of 48, 50, 55, 60, 65, or 70 hours. Excessive drying time increases equipment uptime, leading to higher energy consumption and costs. It also prolongs the entire production cycle and reduces efficiency. Insufficient drying time results in higher moisture content in the product, making it more susceptible to spoilage during storage. Products with high moisture content exhibit poor stability during long-term storage and may degrade. Furthermore, inadequate drying can lead to poor solubility upon rehydration, affecting usability.

[0027] Optionally, the composite nano-silicon particle gel is calcined and ground to obtain a carbon-silicon composite material, including:

[0028] The composite nano-silicon particle gel was placed in a crucible and then placed in a tube furnace under an inert gas atmosphere for calcination at a temperature of 500℃ to 1200℃ for 4 hours to 10 hours.

[0029] The calcination temperature can be selected as 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃ or 1200℃. The calcination time can be 4h, 5h, 6h, 7h, 8h, 9h or 10h.

[0030] The calcined product was refined using a grinding mill to obtain a carbon-silicon composite material.

[0031] Optionally, the crucible capacity can be from 100 mL to 500 mL, and the inert gas can include nitrogen, helium, argon, a 5% argon-hydrogen mixture, etc. The sand mill can be a MicroMedia Invicta.

[0032] On the other hand, the present invention also provides a carbon-silicon composite material prepared using the aforementioned method for preparing silicon composite materials. In the carbon-silicon composite material, nano-silicon particles are embedded within the framework structure of carbon materials.

[0033] On the other hand, the present invention also provides a negative electrode containing a carbon-silicon composite material, including the carbon-silicon composite material prepared by the above method.

[0034] On the other hand, the present invention also provides a battery comprising a positive electrode, an electrolyte membrane and a negative electrode stacked in sequence, wherein the negative electrode is the aforementioned negative electrode containing a carbon-silicon composite material.

[0035] Compared with existing technologies, the preparation method of the carbon-silicon composite material, the carbon-silicon composite material, the negative electrode, and the battery provided by this invention achieve at least the following beneficial effects:

[0036] This invention uses hydrogen bonding to uniformly disperse hydroxylated silicon nanoparticles in a gel solution, avoiding the aggregation of silicon nanoparticles. After the gel solidifies and forms, the silicon nanoparticles can be stably contained in the gel skeleton, and subsequent manufacturing processes will not cause the silicon nanoparticles to aggregate.

[0037] During the gel formation process, nano-silicon is encapsulated within the gel. After high-temperature pyrolysis, the nano-silicon embeds into the carbon framework. Compared to existing methods involving silicon-carbon mixing and silicon deposition on a carbon substrate, the interaction between the nano-silicon and the carbon framework is stronger in this invention. The nano-silicon does not detach from the carbon framework during the electrochemical reactions of charge and discharge. The embedding of nano-silicon within the carbon framework enhances the contact between the nano-silicon particles and the carbon material, effectively improving the electronic conductivity of the nano-silicon particles. Furthermore, it does not detach from the carbon material and lose electrical contact during multiple charge-discharge cycles, thus improving the electrochemical performance of nano-silicon particles as a negative electrode in lithium-ion batteries.

[0038] In this invention, nano-silicon particles are embedded inside carbon materials, and a carbon film is formed on the surface of the nano-silicon particles, which can effectively alleviate the volume expansion of the nano-silicon particles.

[0039] The presence of nano-silicon particles within the framework of carbon materials effectively prevents direct contact between the silicon material and the electrolyte, reducing the consumption of electrolyte by the unstable solid electrolyte membrane.

[0040] Compared to the cumbersome method of combining silicon and carbon materials and simultaneously coating silicon with carbon in the existing technology, the present invention achieves the combination of silicon and carbon materials and the coating of carbon film in one step of pyrolysis. The operation method is simple and reduces costs.

[0041] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0042] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0043] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0044] Figure 1 Scanning electron microscope (SEM) images of silicon nanoparticles with a particle size between 50 and 100 nm.

[0045] Figure 2 This is a scanning electron microscope image of the silicon-carbon material composed of gel-pyrolyzed carbon composite nanoparticles in Example 1;

[0046] Figure 3 This is a schematic diagram showing the bonding between hydroxylated nanosilicon materials and acrylamide monomers via hydrogen bonding.

[0047] Figure 4 The XRD spectra of silicon nanoparticles (Si), gel pyrolytic carbon (Gel-C), and gel pyrolytic carbon composite silicon nanoparticles (Si@Gel-C) are shown, where ▲ represents the characteristic peak of carbon and ★ represents the characteristic peak of silicon.

[0048] Figure 5 The cycling performance curve of the half-cell assembled from the carbon-silicon composite material in Example 1 after 210 cycles at a current density of 2.0 A / g. Detailed Implementation

[0049] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0050] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0051] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0052] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0053] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0054] Example 1:

[0055] This embodiment provides a method for preparing a silicon-carbon material (carbon-silicon composite material) of gel-pyrolyzed carbon composite nanoparticles, which is prepared according to the following steps:

[0056] S101, add 1.0g of nano-silicon powder to 500mL of deionized water, disperse by ultrasonication, then add 20g of ammonia water, disperse by ultrasonication, and then stir by high-speed magnetic stirring for 2h to hydroxylate the nano-silicon powder. Dry the treated nano-silicon powder (i.e., hydroxylated nano-silicon material) for later use.

[0057] The ammonia water here is a hydroxylation reagent, and the ratio of the hydroxylation reagent to the nano-silicon powder is 1:5 to 1:30, which is not specifically limited here.

[0058] Scanning electron microscope (SEM) images of silicon nanoparticles with a particle size between 50 and 100 nm are shown below. Figure 1 As shown. Figure 1 The accelerating voltage EHT is 1500kV, the working distance WD is 100mm, and the amplification factor Mag is 11808KX.

[0059] S102, add 1.0g of acrylamide and 5mg of N,N-methylenebisacrylamide to 50mL of deionized water and stir magnetically until completely dissolved to obtain a mixed solution of gel precursors.

[0060] S103, 0.5g of the hydroxylated nano-silicon material obtained in step S101 is added to the gel precursor mixture obtained in step S102, and ultrasonically dispersed and magnetically stirred for 4h. Then, the resulting uniform dispersion is poured into a polyether ether ketone mold and heated at 100°C for 10h to initiate the cross-linking polymerization of the monomers, thereby obtaining a gel containing nano-silicon material.

[0061] A schematic diagram showing the hydrogen bonding between hydroxylated silicon nanomaterials and acrylamide monomers is shown below. Figure 3 As shown.

[0062] S104. The obtained gel containing nano-silicon was freeze-dried to obtain a composite nano-silicon particle gel. The freeze-drying temperature was -50℃ and the freeze-drying time was 60h.

[0063] S105, the freeze-dried composite nano-silicon particle gel is placed in a tube furnace and heated to 800℃ at a heating rate of 5℃ / min in a protective gas atmosphere. It is then held at 800℃ for 10 hours. The gel can be refined using a sand mill to obtain a silicon-carbon material with gel-pyrolyzed carbon composite nano-silicon particles, i.e., a carbon-silicon composite material. The nano-silicon particles are embedded in the framework structure of the carbon material.

[0064] Scanning electron microscope image of silicon-carbon material composed of gel-pyrolyzed carbon composite nanoparticles as shown below Figure 2 As shown.

[0065] Figure 4 The images show the XRD patterns of silicon nanoparticles (Si), gel-pyrolytic carbon (Gel-C), and gel-pyrolytic carbon composite silicon nanoparticles (Si@Gel-C). ▲ represents the characteristic peaks of carbon, and ★ represents the characteristic peaks of silicon. Figure 4 The horizontal axis 2theta represents the diffraction angle, which is the angle between the incident X-ray and the diffracted ray.

[0066] Example 2:

[0067] This embodiment provides a method for preparing a silicon-carbon material (carbon-silicon composite material) of gel-pyrolyzed carbon composite nanoparticles, which is prepared according to the following steps:

[0068] S201, add 1.0g of nano-silicon powder to 500mL of deionized water and disperse by ultrasonication. Add 5g of ammonia water, disperse by ultrasonication, and then stir with high-speed magnetic force for 2h to hydroxylate the nano-silicon. Dry the treated silicon powder (i.e., hydroxylated nano-silicon material) for later use.

[0069] The ammonia water here is a hydroxylation reagent, and the ratio of the hydroxylation reagent to the nano-silicon powder is 1:5 to 1:30, which is not specifically limited here.

[0070] S202, add 1.0g of polyvinyl alcohol to 50mL of deionized water, heat to 100℃, and stir magnetically until the polyvinyl alcohol is completely dissolved to obtain a gel precursor mixed solution.

[0071] S203: The gel precursor mixture obtained in step S202 is then mixed with 0.5g of the hydroxylated nano-silicon material obtained in step S101, and ultrasonically dispersed and magnetically stirred for 4h. 2mL of glutaraldehyde is added to initiate the crosslinking reaction, and the resulting uniform dispersion is quickly poured into a polyether ether ketone mold. The mixture is heated at 100℃ for 10h to initiate the crosslinking polymerization of the monomers. After cooling and molding, a gel containing nano-silicon material is obtained.

[0072] S204, the obtained gel containing nano-silicon was freeze-dried at -60℃ for 48 hours.

[0073] S205, the freeze-dried gel is placed in a tube furnace and heated to 1200℃ at a heating rate of 5℃ / min in a protective gas atmosphere, and held at 1200℃ for 4h to obtain a silicon-carbon material of gel pyrolysis carbon composite nano-silicon particles, i.e., a carbon-silicon composite material.

[0074] Example 3:

[0075] This embodiment provides a method for preparing a silicon-carbon material (carbon-silicon composite material) of gel-pyrolyzed carbon composite nanoparticles, which is prepared according to the following steps:

[0076] S301: Add 1.0 g of nano-silicon powder to 500 mL of deionized water and disperse by ultrasonication. Add 30 g of ethoxytrimethylsilane, disperse by ultrasonication, and then stir with high-speed magnetic stirring for 2 h to hydroxylate the nano-silicon. Dry the treated silicon powder for later use.

[0077] Here, ethoxytrimethylsilane is a hydroxylating agent, and the ratio of the hydroxylating agent to nano-silicon powder is 1:5 to 1:30;

[0078] S302: Add 1.0g of acrylamide and 5mg of N,N-methylenebisacrylamide to 50mL of deionized water and stir magnetically until completely dissolved to obtain a mixed solution of gel precursors.

[0079] S303, 1g of the hydroxylated nano-silicon material obtained in step S301 is added to the gel precursor mixture obtained in step S302, and ultrasonically dispersed and magnetically stirred for 4h. Then, the resulting uniform dispersion is poured into a polyether ether ketone mold and heated at 100°C for 10h to initiate the cross-linking polymerization of the monomers, thereby obtaining a gel containing nano-silicon material.

[0080] S304, the obtained gel containing nano-silicon was freeze-dried to obtain composite nano-silicon particle gel. The freeze-drying temperature was -40℃ and the freeze-drying time was 72h.

[0081] S305, the freeze-dried composite nano-silicon particle gel is placed in a tube furnace and heated to 1000℃ at a heating rate of 5℃ / min in a protective gas atmosphere. It is then held at 1000℃ for 6 hours. The gel can be refined by a sand mill to obtain a silicon-carbon material of gel pyrolysis carbon composite nano-silicon particles, i.e., a carbon-silicon composite material.

[0082] Example 4:

[0083] This embodiment provides a method for preparing silicon-carbon materials (carbon-silicon composite materials) of gel-pyrolyzed carbon composite nanoparticles, which is prepared according to the following steps:

[0084] S401: First, add 1.0g of nano-silicon powder to 500mL of deionized water and disperse it by ultrasonication. Then add 10g of trimethoxysilane, disperse it by ultrasonication, and then stir it with high-speed magnetic force for 5h to hydroxylate the nano-silicon. Dry the treated silicon powder (i.e., hydroxylated nano-silicon material) for later use.

[0085] Trimethoxysilane is the hydroxylating agent, and the ratio of the hydroxylating agent to the nano-silicon powder is 1:5 to 1:30, which is not specifically limited here.

[0086] S402: Add 1.0g of acrylamide and 5mg of N,N-methylenebisacrylamide to 50mL of deionized water and stir magnetically until completely dissolved to obtain a gel precursor mixed solution.

[0087] S403, 0.5g of the hydroxylated nano-silicon material obtained in step S101 is added to the gel precursor mixture obtained in step S102, and the mixture is ultrasonically dispersed and magnetically stirred for 4h. Then, the resulting uniform dispersion is poured into a polyether ether ketone mold and heated at 100°C for 10h to initiate the cross-linking polymerization of the monomers, thereby obtaining a gel containing nano-silicon material.

[0088] S404, the obtained gel containing nano-silicon was freeze-dried to obtain composite nano-silicon particle gel, the freeze-drying temperature was -50℃ and the freeze-drying time was 48h.

[0089] S405, the freeze-dried composite nano-silicon particle gel is placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min in a protective gas atmosphere. It is then held at 500℃ for 10 hours. The gel can be refined by a sand mill to obtain a silicon-carbon material of gel pyrolysis carbon composite nano-silicon particles, i.e., a carbon-silicon composite material.

[0090] Comparative Example 1:

[0091] The comparative example provides a method for preparing a silicon-carbon material comparative sample, which is made according to the following steps:

[0092] D101, add 1.0g of acrylamide and 5mg of N,N-methylenebisacrylamide to 50mL of deionized water and stir magnetically until completely dissolved to obtain a gel precursor mixed solution.

[0093] D102, 0.5g of nano-silica powder was added to the gel precursor mixture solution, and ultrasonic dispersion and magnetic stirring were performed for 4h. Then the resulting uniform dispersion was poured into a polyether ether ketone mold and heated at 100℃ for 10h to initiate the cross-linking polymerization of the monomers, thus obtaining a nano-silica gel.

[0094] D103, the obtained gel containing nano-silicon was freeze-dried at -50℃ for 48 hours.

[0095] D104: The freeze-dried gel was placed in a tube furnace and heated to 1000℃ at a heating rate of 5℃ / min in a protective gas atmosphere. The temperature was then maintained at 1000℃ for 6 hours to obtain silicon-carbon material.

[0096] In Comparative Example 1, the nano-silicon powder was not hydroxylated, unlike Examples 1 to 4.

[0097] Comparative Example 2:

[0098] The comparative example provides a method for preparing a silicon-carbon material comparative sample, which is made according to the following steps:

[0099] D201: Add 1.0g of nano-silicon powder to 500mL of deionized water and disperse by ultrasonication. Add 10g of trimethoxysilane, disperse by ultrasonication, and then stir with high-speed magnetic force for 5h to hydroxylate the nano-silicon. Dry the treated nano-silicon powder for later use.

[0100] D202: Add 0.4g of citric acid to 500mL of deionized water and stir magnetically until completely dissolved. Add 0.5g of nano-silicon powder obtained in step D201 and disperse ultrasonically for 1h. Then, centrifuge and dry by forced air to obtain the precursor material.

[0101] D203: The precursor material obtained in step D202 is placed in a tube furnace and heated to 1000°C at a heating rate of 5°C / min in a protective gas atmosphere. The temperature is then maintained at 1000°C for 6 hours to obtain silicon-carbon material with conventional carbon source pyrolysis carbon composite nano-silicon particles.

[0102] In this comparative example, compared to Examples 1 to 4, the nano-silicon was hydroxylated, but instead of being freeze-dried, it was directly pyrolyzed in a tube furnace using a conventional carbon source.

[0103] Comparison of experimental results:

[0104] The silicon-carbon material (i.e., carbon-silicon composite material) of gel pyrolytic carbon composite nanoparticles prepared in Example 1 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material: acetylene black: polyvinylidene fluoride of 8:1:1. The mixture was ground into a uniform slurry and coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode and the lithium metal sheet was used as the counter electrode to assemble a CR2025 button cell. The specific capacity was tested at a current density of 0.1 A / g and the cycle performance was tested at a current density of 2.0 A / g. Figure 5 The image shows the cycling performance curve of the half-cell assembled from the carbon-silicon composite material in Example 1 after 210 cycles at a current density of 2.0 A / g. Figure 5 The horizontal axis represents the number of cycles, the vertical axis represents the specific capacity, and the right vertical axis represents the capacity retention rate. Figure 5 The blue curve represents the specific capacity during the cycle. Figure 5 The orange line represents the capacity ratio during cycling. The test results show that the specific capacity is 560.8 mAh / g at a current density of 0.1 A / g; at a current density of 2.0 A / g, after 210 cycles, the specific capacity is maintained at 326.1 mAh / g, with a capacity retention of 91.7% and a coulombic efficiency of 99.6%.

[0105] The silicon-carbon material (i.e., carbon-silicon composite material) of gel pyrolytic carbon composite nanoparticles prepared in Example 2 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material: acetylene black: polyvinylidene fluoride of 8:1:1, mixed and ground into a uniform slurry, and coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode, and a lithium metal sheet as the counter electrode, and a CR2025 button cell was assembled. Specific capacity was tested at a current density of 0.1 A / g, and cycle performance was tested at a current density of 2.0 A / g. The test results showed that the specific capacity at a current density of 0.1 A / g was 541.7 mAh / g; at a current density of 2.0 A / g, after 210 cycles, the specific capacity remained at 294.1 mAh / g, with a capacity retention of 88.3% and a coulombic efficiency of 99.4%.

[0106] The silicon-carbon material of the gel pyrolytic carbon composite nanoparticles prepared in Example 3 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material: acetylene black: polyvinylidene fluoride of 8:1:1, mixed and ground into a uniform slurry, and coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode, and a lithium metal sheet as the counter electrode, and a CR2025 button cell was assembled. Specific capacity was tested at a current density of 0.1 A / g, and cycle performance was tested at a current density of 2.0 A / g. The test results showed that the specific capacity at a current density of 0.1 A / g was 1021.2 mAh / g; after 210 cycles at a current density of 2.0 A / g, the specific capacity remained at 613.8 mAh / g, with a capacity retention of 84.3% and a coulombic efficiency of 99.4%.

[0107] The silicon-carbon material of the gel pyrolytic carbon composite nanoparticles prepared in Example 4 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material: acetylene black: polyvinylidene fluoride of 8:1:1, mixed and ground into a uniform slurry, and coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode, and a lithium metal sheet as the counter electrode, and a CR2025 button cell was assembled. Specific capacity was tested at a current density of 0.1 A / g, and cycle performance was tested at a current density of 2.0 A / g. The test results showed that the specific capacity at a current density of 0.1 A / g was 541.7 mAh / g; at a current density of 2.0 A / g, after 210 cycles, the specific capacity remained at 301.2 mAh / g, with a capacity retention of 90.2% and a coulombic efficiency of 99.6%.

[0108] The silicon-carbon material prepared in Comparative Example 1 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material:acetylene black:polyvinylidene fluoride of 8:1:1, mixed and ground into a uniform slurry, which was then coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode, and a lithium metal sheet as the counter electrode, to assemble a CR2025 button cell. Specific capacity was tested at a current density of 0.1 A / g, and cycle performance was tested at a current density of 2.0 A / g. The test results showed that the specific capacity at 0.1 A / g was 552.4 mAh / g; after 210 cycles at a current density of 2.0 A / g, the specific capacity remained at 284.1 mAh / g, with a capacity retention of 76.3% and a coulombic efficiency of 99.2%.

[0109] The silicon-carbon material prepared in Comparative Example 2 was used as the active material. It was added to N-methylpyrrolidone in a mass ratio of active material:acetylene black:polyvinylidene fluoride of 8:1:1, mixed and ground into a uniform slurry, which was then coated onto copper foil to prepare a lithium-ion battery anode. The silicon-carbon anode was used as the working electrode, and a lithium metal sheet as the counter electrode, to assemble a CR2025 button cell. Specific capacity was tested at a current density of 0.1 A / g, and cycle performance was tested at a current density of 2.0 A / g. The test results showed that the specific capacity at a current density of 0.1 A / g was 501.6 mAh / g; at a current density of 2.0 A / g, after 210 cycles, the specific capacity remained at 224.4 mAh / g, with a capacity retention of 67.4% and a coulombic efficiency of 98.9%.

[0110] Capacity retention rate refers to the ratio of the specific capacity of a battery after multiple cycles to its initial specific capacity, while coulombic efficiency refers to the ratio of the discharged capacity to the charged capacity during the charging and discharging process. Compared with Comparative Examples 1 and 2, the capacity retention rates of the carbon-silicon composite materials obtained in Examples 1 to 4 of the present invention are all much higher than those in Comparative Examples 1 and 2, indicating that the carbon-silicon composite materials obtained by the present invention have excellent electrochemical performance, especially their excellent cycle stability and coulombic efficiency at high current densities.

[0111] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of the invention. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. A method for producing a carbon-silicon composite material, characterized by, include: The preparation of hydroxylated silicon nanomaterials includes: dispersing silicon nanoparticles in deionized water, adding a hydroxylation reagent, performing ultrasonic dispersion, and hydroxylating the silicon nanoparticles to obtain the hydroxylated silicon nanomaterials. The preparation of a gel precursor mixed solution includes: dissolving a gel precursor and a crosslinking agent to obtain a gel precursor mixed solution; The preparation of a gel containing nano-silicon materials includes: adding the hydroxylated nano-silicon materials to the gel precursor mixture solution, heating to a preset temperature to initiate a curing reaction, and obtaining a gel containing nano-silicon materials; Freeze-dry the gel containing the nano-silicon material to obtain a composite nano-silicon particle gel. The composite nano-silicon particle gel was calcined and then ground to obtain a carbon-silicon composite material. In the step of preparing hydroxylated silicon nanomaterials, the mass ratio of the hydroxylating agent to the silicon nanoparticles is 1:5 to 1:

30. The gel precursor includes at least one of sodium acrylate, acrylamide, vinyl alcohol, methyl methacrylate, and sodium carboxymethyl cellulose. The gel includes at least one of the following: sodium polyacrylate gel, polyacrylamide gel, polyvinyl alcohol gel, polymethyl methacrylate gel, and sodium carboxymethyl cellulose gel.

2. The method for producing a carbon-silicon composite material according to claim 1, characterized by, The hydroxylating agent includes at least one of trichlorosilane, trimethoxysilane, ethoxytrimethylsilane, chloromethyltriethoxysilane, ammonia, phytic acid, formaldehyde, methanol, ethanol, sodium hydroxide, and potassium hydroxide.

3. The method of claim 1, wherein the carbon-silicon composite is prepared by a process comprising: The crosslinking agent includes at least one of N,N-thionyldicarboxamide, ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, ethylene oxide, glutaraldehyde, silicon dioxide, and N,N-methylenebisacrylamide. The mass ratio of the gel precursor to the crosslinking agent is from 100:1 to 1000:

1.

4. The method of claim 1, wherein the carbon-silicon composite is prepared by a process comprising: In the step of preparing the gel containing nano-silicon materials: The mass ratio of the hydroxylated nanosilicon material to the gel precursor is 1:2 to 1:

20. The hydroxylated nanosilicon material is added to the gel precursor mixture solution, ultrasonically dispersed evenly, and heated at a temperature of 60°C to 120°C for 6 to 12 hours.

5. The method of claim 1, wherein the carbon-silicon composite is prepared by a process comprising: providing a silicon-containing material; providing a carbon-containing material; and combining the silicon-containing material and the carbon-containing material to form the carbon-silicon composite. The freeze-drying temperature is -60℃ to -40℃, the freeze-drying pressure is 0.5kPa to 50kPa, and the freeze-drying time is 48h to 72h.

6. The method of claim 1, wherein the carbon-silicon composite is prepared by a process comprising: The calcination and grinding of the composite nano-silicon particle gel yields a carbon-silicon composite material, comprising: The composite nano-silicon particle gel was placed in a crucible and then placed in a tube furnace under an inert gas atmosphere for calcination at a temperature of 500°C to 1200°C for 4 to 10 hours. The calcined product is refined by grinding to obtain the carbon-silicon composite material.

7. A carbon-silicon composite material, characterized by, The silicon composite material was prepared using the preparation method according to any one of claims 1 to 6.

8. A negative electrode comprising a carbon-silicon composite material, characterized by The carbon-silicon composite material prepared by the method according to any one of claims 1 to 6.

9. A battery, characterized by It includes a positive electrode, an electrolyte membrane, and a negative electrode stacked in sequence, wherein the negative electrode is the negative electrode containing a carbon-silicon composite material as described in claim 8.

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