Preparation method of carbon-silicon composite material, carbon-silicon composite material, negative electrode and battery

Abstract

The invention discloses a preparation method of a carbon-silicon composite material, the carbon-silicon composite material, a negative electrode and a battery, and the preparation method of the carbon-silicon composite material comprises the following steps: preparing a hydroxylated nano-silicon material, preparing a gel precursor mixed solution, preparing gel containing the nano-silicon material, freeze-drying the gel containing the nano-silicon material, calcining, grinding and refining. The carbon-silicon composite material is obtained. According to the preparation method, hydroxylation treatment is carried out on a nano silicon material, hydrogen-bond interaction is generated between nano silicon particles with the surfaces rich in hydroxyl and gel, the nano silicon material is added into a precursor solution of the gel for ultrasonic dispersion, then a cross-linking agent is added for cross-linking curing of the gel, the nano silicon material can be evenly distributed in a framework of the gel, and the gel is prepared. The contact between the nanometer silicon material and the carbon material is enhanced, the electronic conductivity of the nanometer silicon is effectively improved, the nanometer silicon cannot be separated from the carbon material to lose electric contact in multiple charging and discharging processes, and the electrochemical performance of the battery negative electrode can be improved.

Description

Technical Field

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

[0002] With the vigorous development of the new energy industry, people have put forward higher requirements for the energy density of batteries. The theoretical gram capacity of the widely used graphite negative electrode is 372mAh / g, which has reached the capacity bottleneck, and it is urgent to develop negative electrode materials with higher capacity. Silicon material is considered to be the most promising next-generation negative electrode material for lithium-ion batteries because of its theoretical gram capacity of 4200mAh / g. However, the serious volume change of silicon material during charging and discharging (up to 300%), the formation of unstable solid electrolyte film (SEI film), and poor electronic conductivity hinder the use of silicon material as negative electrode for lithium-ion batteries. Although reducing the size of silicon material and preparing nano-scale silicon material can alleviate the volume expansion problem of silicon, it is still not enough in practical applications.

[0003] In response to the above problems, researchers have also carried out a lot of modification work. The preparation of silicon-carbon composite materials is an effective way to improve the performance of silicon materials used as negative electrodes for lithium-ion batteries. In addition, the composite of silicon and carbon substrate in conventional silicon-carbon materials is only a simple physical contact. During the electrochemical reaction, nano-silicon easily falls off and loses electrical contact. In the process of modifying silicon materials by preparing silicon-carbon materials, nano-silicon particles are prone to agglomeration due to their small particle size, resulting in poor modification effect. Although the commonly used spray method and vapor deposition method can disperse nano-silicon particles better, the preparation cost is high.

[0004] Therefore, there is an urgent need to provide a method for preparing a carbon-silicon composite material that can prevent nano-silicon particles from agglomerating and prevent nano-silicon from falling off 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 are used to prevent nano-silicon particles from agglomerating and prevent nano-silicon particles from falling off the carbon material during the electrochemical reaction of charging and discharging, while reducing costs.

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

[0007] The preparation of hydroxylated nano-silicon material comprises: dispersing nano-silicon particles in deionized water, adding a hydroxylation agent, performing ultrasonic dispersion, hydroxylating the nano-silicon particles, and obtaining the hydroxylated nano-silicon material;

[0008] Preparing a gel precursor mixed solution, including: dissolving a gel precursor and a cross-linking agent to obtain a gel precursor mixed solution;

[0009] The preparation of the gel containing the nano-silicon material comprises: adding the hydroxylated nano-silicon material into the gel precursor mixed solution, heating it to a preset temperature to initiate a curing reaction, and obtaining the gel containing the nano-silicon material;

[0010] freeze-drying the gel containing the nano-silicon material to obtain a composite nano-silicon particle gel;

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

[0012] Optionally, the particle size of nano silicon particles ranges from 50nm to 300nm. If the particle size is too small, the silicon particles will be severely agglomerated, resulting in a smaller specific surface area of ​​the material, which affects the electrochemical performance of the material. If the particle size is too large, the silicon particles are easily broken and pulverized during the charge and discharge process, and the electrochemical performance will decay rapidly.

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

[0014] Optionally, in the step of preparing hydroxylated nano-silicon material, the mass ratio of hydroxylation agent to nano-silicon particles is 1:5 to 1:30, and optionally, the ratio of hydroxylation agent to nano-silicon particles is 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. If it is lower than 1:30, the hydroxyl groups on the surface of nano-silicon powder will be too few, and the effect of hydroxylation of silicon powder will not be obvious, and the subsequent silicon powder will not be well combined with gel through hydrogen bonding force. If it is higher than 1:5, it will cause waste of hydroxylation agent, and the ratio of hydroxylation agent to nano-silicon particles is 1:5 to 1:30, and nano-silicon particles can achieve good hydroxylation. Adding too much hydroxylation agent has little effect on the hydroxylation treatment of nano-silicon powder, which will only cause waste of hydroxylation 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-dithiodicarbonamide, ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, ethylene oxide, glutaraldehyde, silicon dioxide and N,N-methylenebisacrylamide;

[0017] The mass ratio of the gel precursor to the crosslinking agent is 100:1 to 1000:1, and optionally, the mass ratio of the gel precursor to the crosslinking agent is 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, or 1000:1. If the crosslinking agent is too little, the gel preparation will fail, and the aqueous solution of the dissolved gel precursor will not form a gel-like solid. If the crosslinking agent is too much, the polymerization reaction of the gel precursor will be completed very quickly, and the rapid gelation process will make the generated gel less uniform, and the local gel polymerization degree will be inconsistent, resulting in differences in the properties of the gel.

[0018] Optionally, the gel precursor is dissolved by adding the gel precursor to deionized water, and the mass ratio of the gel precursor to the deionized water is 1:10 to 1:50. Optionally, the mass ratio of the gel precursor to the deionized water is 1:10, 1:20, 1:30, 1:40, or 1:50. If too much gel precursor is added, the gel precursor will not be completely dissolved, affecting the preparation of a uniform gel. If too much deionized water is added, the average concentration value of the gel precursor will decrease, resulting in the inability to form a gel.

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

[0020] The mass ratio of the hydroxylated nano-silicon material to the gel precursor is 1:2 to 1:20, and optionally, the mass ratio of the hydroxylated nano-silicon material to the 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 nano-silicon material is added to the gel precursor mixed solution, ultrasonically dispersed uniformly, heated at 60°C to 120°C, and heated for 6h to 12h.

[0021] If too few hydroxylated nano-silicon particles are added, which is lower than the minimum value, the specific capacity of the prepared silicon-carbon composite material will be too low, and the high capacity characteristics of the silicon-carbon negative electrode will not be exhibited. If too many hydroxylated nano-silicon particles are added, the gel will not be able to wrap the nano-particles well, and too many nano-silicon particles will be exposed, or even not loaded on the gel skeleton, so the effect of improving the electrochemical performance of the nano-silicon particles will not be achieved, resulting in a rapid degradation of the performance of the prepared silicon-carbon negative electrode material.

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

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

[0024] The freeze drying temperature is -60℃ to -40℃, and the options are -60℃, -55℃, -50℃, -45℃ or -40℃. Temperatures below -60℃ will slow down the speed at which water sublimates directly from solid to gas, resulting in a longer drying cycle and reduced efficiency. Running the freeze dryer for a long time, especially under conditions below the 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 may dry slowly, resulting in uneven drying and affecting product quality.

[0025] The freeze drying pressure is 0.5kPa to 50kPa, and the optional freeze drying pressure is 0.5kPa, 1kPa, 2kPa, 3kPa, 4kPa, 5kPa, 10kPa, 15kPa, 20kPa, 25kPa, 30kPa, 35kPa, 40kPa, 45kPa or 50kPa. If it is lower than 0.5kPa, the equipment load will increase, and the vacuum pump will need to do more work to maintain a high vacuum degree, which will increase energy consumption and shorten the service life of the vacuum pump. Under extremely high vacuum degrees, the gas in the sample may expand and escape rapidly, which may damage the microstructure of the product. In some cases, too high a vacuum degree may cause a decrease in the drying rate because the rate at which water vapor escapes from the surface of the product may exceed the rate at which internal moisture migrates to the surface. If it is higher than 50kPa, it will slow down the rate at which moisture sublimates from the product and reduce the drying efficiency. The moisture in the product may not be effectively removed, resulting in excessive moisture content in the final product, affecting the stability of the product. If it is too much higher than the maximum value, the temperature in the system may approach or exceed the melting point of ice, causing ice crystals to melt into water, causing changes in the sample structure and loss of active ingredients. At lower negative pressures, in order to maintain a certain drying rate, it may be necessary to increase the temperature of the drying chamber, thereby increasing energy consumption.

[0026] The freeze drying time is 48h to 72h, and the optional freeze drying time is 48h, 50h, 55h, 60h, 65h or 70h. Too long drying time means increased equipment operation time, resulting in increased energy consumption and costs. Too long drying time will extend the entire production cycle and reduce production efficiency. Too short drying time will cause the product to contain more moisture, causing the product to easily deteriorate during storage. Products with high moisture content have poor stability during long-term storage and may degrade. In addition, insufficient drying may cause the product to have poor solubility when rehydrated, affecting the use effect.

[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 is placed in a crucible, and placed in a tube furnace under an inert gas atmosphere for calcination at a temperature of 500° C. to 1200° C. for a calcination time of 4 h to 10 h;

[0029] The calcination temperature may be 500° C., 600° C., 700° C., 800° C., 900° C., 1000° C., 1100° C. or 1200° C. The calcination time may be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h.

[0030] The calcined product is refined by a grinder to obtain a carbon-silicon composite material.

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

[0032] On the other hand, the present invention also provides a carbon-silicon composite material, which is prepared by the above-mentioned method for preparing the silicon composite material. In the carbon-silicon composite material, nano-silicon particles are embedded in the skeleton structure of the carbon material.

[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 negative electrode containing the carbon-silicon composite material.

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

[0036] The present invention evenly disperses hydroxylated nano silicon particles in a gel solution through hydrogen bonding, thereby avoiding agglomeration of the nano silicon particles. After the gel is cured and formed, the nano silicon particles can be stabilized in the gel skeleton, and subsequent production processes will not lead to agglomeration of the nano silicon particles.

[0037] During the gel forming process, nano silicon is encapsulated in the gel, and after high temperature pyrolysis, the nano silicon is embedded in the carbon skeleton. Compared with the prior art method of silicon-carbon mixing and silicon deposition on a carbon substrate, the nano silicon in the present invention has a stronger interaction force with the carbon skeleton, and the nano silicon will not separate from the carbon skeleton during the electrochemical reaction of charge and discharge. The nano silicon is embedded in the carbon skeleton, which enhances the contact between the nano silicon particles and the carbon material, effectively improves the electronic conductivity of the nano silicon particles, and will not separate from the carbon material and lose electrical contact during multiple charge and discharge processes, so it can improve the electrochemical performance of the nano silicon particles used as the negative electrode of lithium ion batteries.

[0038] In the present invention, the nano silicon particles are embedded in the carbon material, and there is a layer of carbon film on the surface of the nano silicon particles, which can effectively alleviate the volume expansion of the nano silicon particles.

[0039] Nano-silicon particles inside the skeleton of carbon materials can effectively avoid direct contact between silicon materials and electrolytes, and reduce the consumption of electrolytes by unstable solid electrolyte membranes.

[0040] Compared with the cumbersome method of combining silicon and carbon materials and simultaneously carbon coating silicon in the prior art, the one-step pyrolysis method of the present invention realizes the combination of silicon and carbon materials and the coating of carbon film, and the operation method is simple and the cost is reduced.

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

[0042] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0044] Figure 1 This is a scanning electron microscope image of nano silicon particles with a particle size between 50 and 100 nm;

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

[0046] Figure 3 Schematic diagram of the combination of hydroxylated nano-silicon material and acrylamide monomer through hydrogen bonding;

[0047] Figure 4 XRD spectra of nano-silicon particles (Si), gel pyrolytic carbon (Gel-C), and gel pyrolytic carbon composite nano-silicon particles (Si@Gel-C), where ▲ represents the characteristic peak of carbon and ★ represents the characteristic peak of silicon;

[0048] Figure 5 This is a cycle performance curve of the half-cell assembled with the carbon-silicon composite material in Example 1 after 210 cycles at a current density of 2.0 A / g. DETAILED DESCRIPTION

[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 the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

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

[0051] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

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

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

[0054] Embodiment 1:

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

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

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

[0058] The scanning electron microscope image of nano-silicon particles with a particle size between 50 and 100 nm is shown below. Figure 1 shown. Figure 1 The accelerating voltage EHT is 1500kV, the working distance WD is 100mm, and the magnification Mag is 11808KX.

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

[0060] S103, add 0.5 g of the hydroxylated nano-silicon material obtained in step S101 to the mixed solution of the gel precursor obtained in step S102, perform ultrasonic dispersion and magnetic stirring for 4 hours, then pour the obtained uniform dispersion into a polyetheretherketone mold, heat at 100°C for 10 hours to initiate cross-linking polymerization of the monomers, and obtain a gel containing the nano-silicon material.

[0061] Schematic diagram of the combination of hydroxylated nano-silicon material and acrylamide monomer through hydrogen bonding. Figure 3 shown.

[0062] S104, freeze-drying the obtained nano-silicon gel to obtain a composite nano-silicon particle gel, with the freeze-drying temperature being -50°C and the freeze-drying time being 60 hours.

[0063] S105, placing the freeze-dried composite nano-silicon particle gel in a tubular furnace, heating it to 800°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 800°C for 10 hours, and then refining it by a sand mill to obtain a silicon-carbon material of the gel pyrolysis carbon composite nano-silicon particles, that is, a carbon-silicon composite material. The nano-silicon particles are embedded in the skeleton structure of the carbon material.

[0064] The scanning electron microscope image of the silicon-carbon material of the gel pyrolysis carbon composite nano-silicon particles is shown in Figure 2 shown.

[0065] Figure 4 XRD spectra of nano-silicon particles (Si), gel pyrolytic carbon (Gel-C), and gel pyrolytic carbon composite nano-silicon particles (Si@Gel-C), where ▲ represents the characteristic peak of carbon and ★ represents the characteristic peak of silicon. Figure 4 The horizontal coordinate 2theta is the diffraction angle, that is, the angle between the incident X-ray and the diffraction line.

[0066] Embodiment 2:

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

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

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

[0070] S202, adding 1.0 g of polyvinyl alcohol into 50 mL of deionized water, heating to 100° C., and magnetically stirring until the polyvinyl alcohol is completely dissolved to obtain a gel precursor mixed solution.

[0071] S203, the mixed solution of the gel precursor obtained in step S202 is then added with 0.5 g of the hydroxylated nano-silicon material obtained in step S101, and ultrasonic dispersion and magnetic stirring are performed for 4 hours. 2 mL of glutaraldehyde is added to initiate a cross-linking reaction, and the uniform dispersion obtained is quickly poured into a mold of polyetheretherketone, heated at 100°C for 10 hours to initiate cross-linking polymerization of the monomers, and cooled to form a gel containing nano-silicon material;

[0072] S204, freeze-drying the obtained nano-silicon-containing gel at a freeze-drying temperature of -60°C for 48 hours.

[0073] S205, placing the freeze-dried gel in a tubular furnace, heating it to 1200°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 1200°C for 4 hours to obtain a silicon-carbon material of gel pyrolysis carbon composite nano-silicon particles, that is, a carbon-silicon composite material.

[0074] Embodiment 3:

[0075] This embodiment provides a method for preparing a silicon-carbon material (carbon-silicon composite material) of gel pyrolysis carbon composite nano-silicon particles, 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 ultrasonic. Add 30 g of ethoxytrimethylsilane, and disperse by ultrasonic. Then, stir by high-speed magnetic stirring for 2 h to perform hydroxylation treatment on the nano silicon. Dry the treated silicon powder for later use.

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

[0078] S302, adding 1.0 g of acrylamide and 5 mg of N,N-methylenebisacrylamide into 50 mL of deionized water, stirring with a magnetic stirrer until completely dissolved, to obtain a gel precursor mixed solution.

[0079] S303, add 1 g of the hydroxylated nano-silicon material obtained in step S301 to the mixed solution of the gel precursor obtained in step S302, perform ultrasonic dispersion and magnetic stirring for 4 hours, then pour the obtained uniform dispersion into a polyetheretherketone mold, heat at 100°C for 10 hours to initiate cross-linking polymerization of the monomers, and obtain a gel containing the nano-silicon material.

[0080] S304, freeze-drying the obtained nano-silicon gel to obtain a composite nano-silicon particle gel, with the freeze-drying temperature being -40°C and the freeze-drying time being 72 hours.

[0081] S305, placing the freeze-dried composite nano-silicon particle gel in a tubular furnace, heating it to 1000°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 1000°C for 6 hours. It can be refined by a sand mill to obtain a silicon-carbon material of the gel pyrolysis carbon composite nano-silicon particles, that is, a carbon-silicon composite material.

[0082] Embodiment 4:

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

[0084] S401, firstly, 1.0 g of nano silicon powder is added to 500 mL of deionized water, and ultrasonic dispersion is performed. 10 g of trimethoxysilane is added, and ultrasonic dispersion is performed, and then high-speed magnetic stirring is performed for 5 hours to perform hydroxylation treatment on the nano silicon, and the treated silicon powder (i.e., hydroxylated nano silicon material) is dried for later use.

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

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

[0087] S403, add 0.5g of the hydroxylated nano-silicon material obtained in step S101 to the mixed solution of the gel precursor obtained in step S102, and perform ultrasonic dispersion and magnetic stirring for 4 hours. Then, pour the obtained uniform dispersion into a polyetheretherketone mold, heat at 100°C for 10 hours to initiate cross-linking polymerization of the monomers, and obtain a gel containing nano-silicon material.

[0088] S404, freeze-drying the obtained nano-silicon gel to obtain a composite nano-silicon particle gel, with the freeze-drying temperature being -50°C and the freeze-drying time being 48 hours.

[0089] S405, placing the freeze-dried composite nano-silicon particle gel in a tubular furnace, heating it to 500°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 500°C for 10 hours. It can be refined by a sand mill to obtain a silicon-carbon material of the gel pyrolysis carbon composite nano-silicon particles, that is, a carbon-silicon composite material.

[0090] Comparative Example 1:

[0091] The preparation method of a silicon-carbon material comparison sample provided in this comparative example is prepared according to the following steps:

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

[0093] D102, add 0.5g of nano-silicon powder to the gel precursor mixed solution, perform ultrasonic dispersion and magnetic stirring for 4h, then pour the obtained uniform dispersion into a polyetheretherketone mold, heat at 100°C for 10h to initiate cross-linking polymerization of the monomers, and obtain nano-silicon gel.

[0094] D103, freeze-drying the obtained nano-silicon gel at -50°C for 48 hours.

[0095] D104, placing the freeze-dried gel in a tubular furnace, heating it to 1000°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 1000°C for 6 hours to obtain a silicon-carbon material.

[0096] Compared with Examples 1 to 4, in Comparative Example 1, the nano-silicon powder was not subjected to hydroxylation treatment.

[0097] Comparative Example 2:

[0098] The preparation method of a silicon-carbon material comparison sample provided in this comparative example is prepared according to the following steps:

[0099] D201, add 1.0g of nano silicon powder to 500mL of deionized water, and disperse by ultrasonic. Add 10g of trimethoxysilane, and disperse by ultrasonic. Then, stir by high-speed magnetic stirring for 5h, hydroxylate the nano silicon, and dry the treated nano silicon powder for later use.

[0100] D202, add 0.4 g of citric acid into 500 mL of deionized water, stir magnetically until completely dissolved, add 0.5 g of nano silicon powder obtained in step D201, ultrasonically disperse for 1 hour, then centrifuge and blow dry to obtain a precursor material.

[0101] D203, placing the precursor material obtained in step D202 in a tubular furnace, heating it to 1000°C at a heating rate of 5°C / min in a protective gas atmosphere, and keeping it at 1000°C for 6 hours to obtain a silicon-carbon material of conventional carbon source pyrolysis carbon composite nano-silicon particles.

[0102] In this comparative example, compared with Examples 1 to 4, the nano-silicon was subjected to hydroxylation treatment, but freeze-dried, and directly pyrolyzed using a conventional carbon source in a tube furnace.

[0103] Comparison of experimental results:

[0104] The silicon-carbon material (i.e., carbon-silicon composite material) of the gel pyrolysis carbon composite nano-silicon particles prepared in Example 1 was used as an active substance and added into N-methylpyrrolidone in a mass ratio of 8:1:1 of active substance: acetylene black: polyvinylidene fluoride, mixed and ground into a uniform slurry, which was coated on a copper foil to prepare a lithium ion battery negative electrode; the silicon-carbon negative electrode was used as a working electrode and a metal lithium sheet as a counter electrode to be assembled into a CR2025 button battery, and 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 cycle performance curve of the half-cell assembled with the carbon-silicon composite material in Example 1 after 210 cycles at a current density of 2.0 A / g is shown in FIG. Figure 5 The horizontal axis in the middle is the number of cycles, the vertical axis is the specific capacity, and the vertical axis on the right is the capacity retention rate. Figure 5 The blue curve in the middle shows the specific capacity during the cycle. Figure 5 The orange line in the middle indicates the corresponding capacity ratio during the cycle. The test results show that the specific capacity at a current density of 0.1A / g is 560.8mAh / g; at a current density of 2.0A / g, after 210 cycles, the specific capacity is maintained at 326.1mAh / g, the capacity retention rate is 91.7%, and the coulombic efficiency is 99.6%.

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

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

[0107] The silicon-carbon material of the gel pyrolysis carbon composite nano-silicon particles prepared in Example 4 was used as an active substance, added into N-methylpyrrolidone in a mass ratio of 8:1:1 of active substance: acetylene black: polyvinylidene fluoride, mixed and ground into a uniform slurry, and coated on a copper foil to prepare a lithium ion battery negative electrode; the silicon-carbon negative electrode was used as a working electrode and a metal lithium sheet was used as a counter electrode to assemble into a CR2025 button battery, and the specific capacity was tested at a current density of 0.1A / g; the cycle performance was tested at a current density of 2.0A / g; the test results showed that the specific capacity at a current density of 0.1A / g was 541.7mAh / g; at a current density of 2.0A / g, after 210 cycles, the specific capacity was maintained at 301.2mAh / g, the capacity retention rate was 90.2%, and the coulomb efficiency was 99.6%.

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

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

[0110] The capacity retention rate refers to the ratio of the specific capacity of a battery to the initial specific capacity after multiple cycles, and the coulombic efficiency refers to the ratio of the discharge capacity to the charge capacity of a battery during the charge and discharge 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 much higher than those in Comparative Examples 1 and 2, indicating that the carbon-silicon composite materials obtained in the present invention have excellent electrochemical properties, especially excellent cycle stability and coulombic efficiency at high current density.

[0111] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for preparing a carbon-silicon composite material, characterized in that: include: The method comprises the following steps: dispersing nano silicon particles in deionized water, adding a hydroxylation agent, performing ultrasonic dispersion, and hydroxylating the nano silicon particles to obtain the hydroxylated nano silicon material; Preparing a gel precursor mixed solution, including: dissolving a gel precursor and a cross-linking agent to obtain a gel precursor mixed solution; The method comprises: adding the hydroxylated nano-silicon material to the mixed solution of the gel precursor, heating the mixed solution to a preset temperature to initiate a curing reaction, and obtaining the gel containing the nano-silicon material; freeze-drying the gel containing the nano-silicon material to obtain a composite nano-silicon particle gel; The composite nano-silicon particle gel is calcined and ground to obtain a carbon-silicon composite material.

2. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: The hydroxylation agent includes at least one of trichlorosilane, trimethoxysilane, ethoxytrimethylsilane, chloromethyltriethoxysilane, ammonia water, phytic acid, formaldehyde, methanol, ethanol, sodium hydroxide and potassium hydroxide.

3. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: In the step of preparing the hydroxylated nano-silicon material, the mass ratio of the hydroxylation agent to the nano-silicon particles is 1:5 to 1:

30.

4. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: The gel precursor includes at least one of sodium acrylate, acrylamide, vinyl alcohol, methyl methacrylate, and sodium carboxymethyl cellulose; The crosslinking agent includes at least one of N,N-dithiodicarbonamide, 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 cross-linking agent is 100:1 to 1000:1; The gel comprises at least one of sodium polyacrylate gel, polyacrylamide gel, polyvinyl alcohol gel, polymethyl methacrylate gel and sodium carboxymethyl cellulose gel.

5. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: In the step of preparing the gel containing nano-silicon material: The mass ratio of the hydroxylated nano-silicon material to the gel precursor is 1:2 to 1:

20. The hydroxylated nano-silicon material is added to the gel precursor mixed solution and dispersed evenly by ultrasonication. The heating temperature is 60° C. to 120° C. and the heating time is 6 h to 12 h.

6. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: The freeze-drying temperature is -60°C to -40°C, the freeze-drying pressure is 0.5 kPa to 50 kPa, and the freeze-drying time is 48 h to 72 h.

7. The method for preparing the carbon-silicon composite material according to claim 1, characterized in that: The step of calcining the composite nano-silicon particle gel and grinding it to obtain a carbon-silicon composite material comprises: The composite nano-silicon particle gel is placed in a crucible, and placed in a tube furnace under an inert gas atmosphere for calcination at a temperature of 500° C. to 1200° C. for a calcination time of 4 to 10 hours; The calcined product is refined by a grinder to obtain the carbon-silicon composite material.

8. A carbon-silicon composite material, characterized in that: The silicon composite material is prepared by the preparation method of any one of claims 1 to 7.

9. A negative electrode containing a carbon-silicon composite material, characterized in that: A carbon-silicon composite material prepared by the method described in any one of claims 1 to 7.

10. A battery, characterized in that: The invention comprises a positive electrode, an electrolyte membrane and a negative electrode which are stacked in sequence, and the negative electrode is the negative electrode containing the carbon-silicon composite material as claimed in claim 9.

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