A porous carbon-coated nano-silicon carbon composite material and a preparation method thereof

Abstract

The present invention belongs to the technical field of battery anode materials, and discloses a porous nano-silicon carbon composite material coated with a carbon layer and a preparation method thereof. The preparation method of the porous nano-silicon carbon composite material coated with a carbon layer includes: dispersing nano-silicon and phenolic resin in ethanol respectively to obtain a nano-silicon slurry and a phenolic resin solution, mixing and stirring, and then obtaining a mixed powder through spray drying, and obtaining porous nano-silicon carbon after carbonization treatment; adding the porous nano-silicon carbon into a coal tar pitch solution, stirring and dissolving, then performing ball milling and mixing, and obtaining the porous nano-silicon carbon composite material coated with a carbon layer after carbonization treatment. The preparation method has a simple process flow and low cost. The obtained porous nano-silicon carbon composite material coated with a carbon layer can effectively buffer the volume expansion of nano-silicon particles before and after cycling, avoid the pulverization of silicon particles and the pulverization and shedding of the material from the electrode sheet, and moreover, improve the electronic conductivity, and significantly improve the cycle stability, the first Coulomb efficiency and the cycle Coulomb efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of battery anode materials, and particularly relates to a porous nano-silicon carbon composite material coated with a carbon layer and a preparation method thereof. Background Art

[0002] In the past two decades or more, consumer electronics, electric vehicles, etc. have developed rapidly, making people's lives more convenient. Among them, the rise of electric vehicles has reduced a lot of carbon emissions compared with traditional fuel vehicles, greatly alleviating the greenhouse effect. Lithium-ion batteries have been applied in 3C and EV, and even in the field of electric aircraft, due to their advantages in cycle performance and energy density. However, the capacity of traditional graphite anodes (372 mAh g -1 ) has reached its limit and it is difficult to meet people's demand for endurance. Silicon, as one of the most abundant substances on earth (ranked second in reserves), has an extremely high energy density (4200 mAh g -1 ), attracting the attention of many researchers to silicon-based anodes. The lithium storage capacity of the anode material determines the specific capacity of the anode material. However, after silicon anodes embed lithium ions, they will expand in volume (more than 300%), resulting in a series of problems in applications, such as pulverization of silicon particles, detachment of the anode material from the current collector, and consumption of a large amount of lithium ions in the formation of the SEI film. After the lithium battery anode undergoes long-term cycling, due to the pulverization and separation of silicon particles, the conductive network of the anode will be damaged, causing collapse and losing electrical contact with the current collector. The repeated breakage and formation of the SEI film will lead to continuous consumption of the electrolyte and lithium ions, ultimately resulting in loss of specific capacity and affecting battery performance. At the same time, Si is a semiconductor material with a low electronic conductivity (1.56×10 -3 S / m) and a slow electron transfer rate, which cannot meet the requirements of fast kinetic reactions.

[0003] To reduce the volume expansion of silicon anodes, increase the cycle life, and improve the electronic conductivity, researchers designed to reduce silicon materials to the nanoscale, including structures such as silicon nanoparticles, silicon nanowires, nanosilicon thin films, and porous silicon. Subsequently, conductive elements such as carbon, gold, and copper were coated on the surface of Si to lock the silicon particles in a rigid matrix. The surface coating of nanosilicon can be used to alleviate the problem of volume expansion during its charge and discharge process. In the prior art, phenolic resin was in-situ grown on the surface of silicon particles and carbonized, which could form a carbon layer on the surface of silicon particles to play a buffering and supporting role. However, subsequent etching of silicon with hydrofluoric acid would cause irreversible expansion and contraction of silicon particles. This would cause the stable SEI film formed on the surface to continuously break and regenerate, resulting in the thickening of the electrolyte interface layer (SEI) film, an increase in battery internal resistance, and an increase in polarization. Currently, there is also a technical solution that uses nanosilicon materials with smaller particle sizes and composites them with graphite and carbon materials. This composite structure helps to shorten the transmission distance of lithium ions in the material and can also better inhibit the volume expansion of silicon during cycling, reducing the material fragmentation caused thereby. However, this regulation method using nanosilicon as a raw material also has some potential problems in actual production. Nanosilicon materials are extremely prone to oxidation and deterioration, which poses a certain challenge to ensuring the product yield. In addition, the improvement effect of this composite material on the long-cycle stability of silicon-based anode materials is not very obvious. Therefore, it is necessary to explore a better preparation process to solve the volume expansion problem of silicon-based anode materials in order to improve the cycle stability and rate performance of the battery.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a porous nanosilicon-carbon composite material coated with a carbon layer and its preparation method, aiming to solve the problem of how to reduce the volume expansion of silicon-based anode materials in order to improve the cycle stability and rate performance of the battery.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect of the present invention, a preparation method of a porous nanosilicon-carbon composite material coated with a carbon layer is provided, including the following steps:

[0008] S1. Disperse nanosilicon and phenolic resin in ethanol respectively to obtain a nanosilicon slurry and a phenolic resin solution;

[0009] S2. Mix and stir the nanosilicon slurry and the phenolic resin solution. After forming a mixed slurry, perform spray drying to disperse nanosilicon particles in the phenolic resin to obtain a mixed powder;

[0010] S3. Carry out the first carbonization treatment on the mixed powder in an inert atmosphere to obtain nano-silicon carbide with a porous structure;

[0011] S4. Add coal tar pitch to ethanol and stir, then add the nano-silicon carbide with a porous structure and stir to dissolve, carry out ball milling for mixing, and then carry out the second carbonization treatment to obtain the porous nano-silicon carbide composite material with a carbon-coated layer.

[0012] In step S1, optionally, the particle size of the nano-silicon is 10 - 200 nm.

[0013] Optionally, the mass ratio of the nano-silicon to the phenolic resin is (1:3) - (3:1).

[0014] In step S2, optionally, the process conditions for spray drying are: the inlet temperature for spray drying is 100 - 200 °C, the outlet temperature is 50 - 150 °C, and the spray drying time is 0.5 - 5 h.

[0015] In step S3, optionally, the step of carrying out the first carbonization treatment on the mixed powder in an inert atmosphere specifically includes: placing the mixed powder in a tubular furnace filled with argon, and the heating method is:

[0016] Raise the temperature from room temperature to the first temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0017] Raise the temperature from the first temperature to the second temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0018] Raise the temperature from the second temperature to the third temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0019] Raise the temperature from the third temperature to the first carbonization temperature at a rate of 3 - 10 °C / min and keep it warm for 0.5 - 2 h;

[0020] Among them, the first temperature is 80 - 120 °C, the second temperature is 100 - 140 °C, the third temperature is 120 - 180 °C, and the third temperature > the second temperature > the first temperature.

[0021] Optionally, the first carbonization temperature is 500 - 900 °C.

[0022] In step S4, optionally, the ratio of the mass of the coal tar pitch to the sum of the masses of the nano-silicon and the phenolic resin is 1:(30 - 150).

[0023] Optionally, the solvent is ethanol or toluene.

[0024] In step S4, optionally, the parameter conditions for ball milling and mixing are:

[0025] The ball-to-material ratio is (1:2) to (2:1);

[0026] The forward rotation rate is 300 - 700 rpm, and the forward rotation time is 15 - 60 min;

[0027] The reverse rotation rate is 300 - 700 rpm, and the reverse rotation time is 15 - 60 min.

[0028] In step S4, optionally, the heating method for the second carbonization treatment is as follows:

[0029] Heat from room temperature to the fourth temperature at a heating rate of 5 - 30 °C / min;

[0030] Heat from the fourth temperature to the second carbonization temperature at a heating rate of 5 - 30 °C / min, and keep it warm for 6 h;

[0031] Wherein, the fourth temperature is 400 - 600 °C.

[0032] Optionally, the second carbonization temperature is 800 - 1000 °C.

[0033] In the second aspect of the present invention, there is provided a porous nano-silicon carbon composite material coated with a carbon layer, which is prepared by using the preparation method of the porous nano-silicon carbon composite material coated with a carbon layer described above; the particle size of the porous nano-silicon carbon composite material coated with a carbon layer is 0.1 - 10 μm.

[0034] Beneficial effects:

[0035] In the present invention, small-sized nano-silicon is dispersed in phenolic resin by spray drying to form a composite structure of nano-silicon carbon material. Then, through the carbonization treatment of phenolic resin, pores are generated inside the nano-silicon carbon, and porous nano-silicon carbon is formed, which can effectively buffer the volume expansion of nano-silicon particles before and after cycling, and avoid the pulverization of silicon particles and the powdering and falling off of the material from the electrode sheet. After the porous nano-silicon carbon is coated with a carbon layer obtained by carbonizing coal tar pitch, the electronic conductivity is improved, and the deintercalation and intercalation of lithium ions are also easier, significantly improving the stability of the porous nano-silicon carbon composite material coated with a carbon layer, and greatly improving the initial Coulomb efficiency and cycling Coulomb efficiency. At the same time, the preparation method provided by the present invention has low cost, simple production process, good product effect, and has good commercial application prospects. Description of the drawings

[0036] Figure 1 It is a process schematic diagram of the preparation method of the porous nano-silicon carbon composite material coated with a carbon layer provided by the present invention.

[0037] Figure 2 It is a structural schematic diagram of the porous nano-silicon carbon composite material (Si@PF@CTP - 500 °C) prepared in Example 1 of the present invention.

[0038] Figure 3 This is the scanning electron microscope (SEM) image of the porous nanostructured silicon-carbon (Si@PF) prepared in Example 4 of the present invention.

[0039] Figure 4 This is the SEM image of the porous nanostructured silicon-carbon composite material (Si@PF@CTP-500°C) with a carbon-coated layer prepared in Example 1 of the present invention.

[0040] Figure 5 This is the X-ray diffraction (XRD) image of the porous nanostructured silicon-carbon composite material (Si@PF@CTP-500°C) with a carbon-coated layer prepared in Example 1 of the present invention.

[0041] Figure 6 These are the charge-discharge curves of the porous nanostructured silicon-carbon composite materials with a carbon-coated layer prepared in Examples 1-4 of the present invention and the nanostructured silicon-carbon material in Comparative Example 1.

[0042] Figure 7 These are the cycling test curves of the porous nanostructured silicon-carbon composite materials with a carbon-coated layer prepared in Examples 1-4 of the present invention and the nanostructured silicon-carbon material in Comparative Example 1. Detailed implementation manners

[0043] The present invention provides a porous nanostructured silicon-carbon composite material with a carbon-coated layer and a preparation method thereof. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0045] The embodiments of the present invention provide a preparation method of a porous nanostructured silicon-carbon composite material with a carbon-coated layer, including the following steps:

[0046] S1. Dispersing nano-silicon and phenolic resin in ethanol respectively to obtain a nano-silicon slurry and a phenolic resin solution;

[0047] S2. Mixing and stirring the nano-silicon slurry and the phenolic resin solution, and performing spray drying after forming a mixed slurry to disperse nano-silicon particles in the phenolic resin to obtain a mixed powder;

[0048] S3. Performing a first carbonization treatment on the mixed powder in an inert atmosphere to obtain a porous nanostructured silicon-carbon;

[0049] S4. Add coal tar pitch into ethanol, stir, then add the nanosilicon carbide with the porous structure and stir to dissolve, perform ball milling for mixing, and then perform a second carbonization treatment to obtain the porous nanosilicon carbide composite material with a carbon-coated layer.

[0050] In the present invention, first, the nanosilicon and phenolic resin are uniformly dispersed together by spray drying method, and then through the carbonization of the phenolic resin, the hydrogen and oxygen elements in the phenolic resin are removed in the form of gas, leaving pores and voids of different sizes, and the carbon element is retained, thus generating nanosilicon carbide with a porous structure (particle size is about 0.01 - 5 μm). The second carbonization is carried out for the coal tar pitch coated on the surface of the nanosilicon carbide. By high temperature, the hydrogen and oxygen elements in the coal tar pitch are removed, leaving carbon and pores, ensuring that there can be a certain transmission path between the inside of the nanosilicon carbide and the electrolyte. Finally, the porous nanosilicon carbide composite material with a carbon-coated layer is obtained.

[0051] In step S1, in some embodiments, the particle size of the nanosilicon is 10 - 200 nm.

[0052] The present invention uses nanosilicon with a small particle size for dispersion, which significantly reduces the volume expansion effect of silicon during the lithium deintercalation and intercalation process.

[0053] In some embodiments, the mass ratio of the nanosilicon to the phenolic resin is (1:3) to (3:1).

[0054] In step S2, in some embodiments, the process conditions of the spray drying are: the inlet temperature of the spray drying is 100 - 200 °C, the outlet temperature is 50 - 150 °C, and the spray drying time is 0.5 - 5 h.

[0055] The present invention uses the spray drying method to disperse nanosilicon particles in the phenolic resin matrix. After carbonization treatment, some pores can be generated and become a porous structure.

[0056] In step S3, in some embodiments, the step of performing the first carbonization treatment on the mixed powder in an inert atmosphere specifically includes: placing the mixed powder in a tubular furnace filled with argon, and the heating method is:

[0057] Raise the temperature from room temperature to the first temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0058] Raise the temperature from the first temperature to the second temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0059] Raise the temperature from the second temperature to the third temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h;

[0060] Raise the temperature from the third temperature to the first carbonization temperature at a rate of 3 - 10 °C / min, and hold for 0.5 - 2 h;

[0061] Among them, the first temperature is 80 - 120 °C, the second temperature is 100 - 140 °C, the third temperature is 120 - 180 °C, and the third temperature > the second temperature > the first temperature.

[0062] In some embodiments, the first carbonization temperature is 500 - 900 °C.

[0063] During the carbonization process of the phenolic resin, the heating stage below the third temperature (120 - 180 °C) is slow heating. The phenolic resin is preheated and gradually begins to decompose. The phenolic resin on the surface of the mixed powder material starts to carbonize first, generating a certain number of micropores and pores. As the heating progresses, the pores gradually extend towards the interior of the material, and the number of pores continuously increases. Hold for a certain period of time to prevent large cracks caused by sudden and excessive temperature changes, resulting in the cracking and pulverization of the electrode material. The low-temperature and slow treatment makes the size and distribution of the pores generated by carbonization more uniform, creating conditions for the subsequent growth and increase of pores. In the heating stage from the third temperature to the first carbonization temperature (500 - 900 °C), increase the heating rate. The decomposition of the phenolic resin accelerates, the thermal weight loss is obvious, a large amount of hydrogen and oxygen are removed, generating a large number of pores and voids. Hold for a period of time to obtain the required porous carbon substrate material, including different numbers of micropores, mesopores, and macropores, creating an effective path for the transmission of lithium ions and having a strong capacity to accommodate and inhibit the volume expansion of nano-silicon.

[0064] In step S4, in some embodiments, the ratio of the mass of the coal tar pitch to the sum of the masses of the nano-silicon and the phenolic resin is 1:(30 - 150). The solvent in the coal tar pitch solution can be ethanol or toluene, but is not limited thereto.

[0065] Coal tar pitch is a kind of soft carbon, which greatly improves the structural stability after carbonization. And in order to reduce the occurrence of side reactions, avoid the etching of Si by HF acid in the electrolyte, and improve the electrode conductivity, industrially low-cost and easily available coal tar pitch is used for carbon coating and carbonization treatment, and a layer of stable soft carbon is further coated. After carbonization, the electronic conductivity is improved and the volume expansion is improved.

[0066] In step S4, in some embodiments, the parameter conditions of the ball milling and mixing are as follows:

[0067] The ball-to-material ratio is (1:2) - (2:1);

[0068] The forward rotation speed is 300 - 700 rpm, and the forward rotation time is 15 - 60 min;

[0069] The reverse rotation speed is 300 - 700 rpm, and the reverse rotation time is 15 - 60 min.

[0070] In step S4, in some embodiments, the heating method of the second carbonization treatment is as follows:

[0071] Heat up from room temperature to the fourth temperature at a heating rate of 5 - 30 °C / min;

[0072] Heat up from the fourth temperature to the second carbonization temperature at a heating rate of 5 - 30 °C / min, and keep warm for 6 h;

[0073] Among them, the fourth temperature is 400 - 600 °C.

[0074] In some embodiments, the second carbonization temperature is 800 - 1000 °C.

[0075] During the carbonization process of coal tar pitch, in the low-temperature carbonization stage below the fourth temperature (400 - 600 °C), the coal tar pitch first starts to undergo thermal cracking of molecules, generating a small amount of carbon and gas. As the temperature rises, the cracking rate of the coal tar pitch increases, generating a large amount of carbon and gas. Gradually, a carbon coating layer is formed and some pores are generated, which is beneficial to the improvement of conductivity and ion diffusion. For the high-temperature carbonization at 800 - 1000 °C, the reaction rate is very fast, generating a large amount of carbon, gas, and pores, forming a complete carbon coating layer with micropore, mesopore, and macropore structures, which plays a role in buffering the volume expansion of nanosilicon and is beneficial to the improvement of electron conductivity and ion conductivity.

[0076] In the second aspect of the present invention, a porous nano-silicon carbon composite material coated with a carbon layer is provided, which is prepared by using the preparation method of the porous nano-silicon carbon composite material coated with a carbon layer.

[0077] In some embodiments, the particle size of the porous nano-silicon carbon composite material coated with a carbon layer is 0.1 - 10 μm.

[0078] The following is a detailed description through specific examples.

[0079] Example 1

[0080] Please refer to Figure 1 the flow chart showing the preparation of the nano-silicon carbon composite material coated with a carbon layer as shown, and the preparation process of this example specifically includes the following steps:

[0081] (1) Si@PF composite powder

[0082] Dispersion of nanosilicon: Dispersion by a homogenizer. Take 150 g of nanosilicon and add 1350 g of absolute ethanol. First, stir and pre-disperse it, and then add it to the homogenizer. Under a pressure of 23000 Psi, homogenize and disperse it once;

[0083] Phenolic resin dissolution: Add 300 g of phenolic resin to 2700 g of absolute ethanol and ultrasonically dissolve for 5 min;

[0084] Compound: Add the well-dispersed nano-silicon slurry and phenolic solution together into a 5 L double-planet stirring kettle, and set the parameters as 40 rpm / 1000 rpm / 30 min;

[0085] Spray process parameters: Inlet temperature 150 °C, outlet temperature 90 °C, atomization disk 280 Hz, fan 25 Hz.

[0086] (2) Carbonization of phenolic resin

[0087] Pass Ar (99.9%) gas into the reaction chamber of the tubular furnace at a rate of 100 ml / min, and heat from room temperature to 1000 °C at a rate of 2 °C / min and hold for 1 h; Heat from 100 °C to 120 °C at a rate of 2 °C / min and hold for 1 h, from 120 °C to 150 °C at a rate of 2 °C / min and hold for 1 h, from 150 °C to 500 °C at a rate of 5 °C / min and hold for 1 h.

[0088] (3) Nano-silicon carbon coated with coal tar pitch

[0089] Take 10 g of coal tar pitch, add 30 g of absolute ethanol, stir and dissolve at room temperature for 10 min, then add 20 g of Si@PF sample and stir and dissolve for 10 min.

[0090] (4) Ball milling and mixing

[0091] Ball-to-material ratio 2:1. Program: Forward rotation for 15 min / 500 rpm, reverse rotation for 15 min / 500 rpm.

[0092] (5) Carbonization of coal tar pitch

[0093] Heat from room temperature to 450 °C at a heating rate of 15 °C / min; Heat from 450 °C to 850 °C at a heating rate of 10 °C / min, hold at 850 °C for 6 h, and then naturally cool to room temperature.

[0094] (6) Collect the black powder to obtain a porous nano-silicon carbon composite material with a carbon-coated layer, denoted as Si@PF@CTP-500 °C.

[0095] As Figure 2 In the schematic diagram of the structure of the porous nano-silicon carbon composite material with a carbon-coated layer (Si@PF@CTP-500 °C) shown: ① is the coal tar pitch carbon coating layer, ② is the phenolic resin carbon substrate, ③ is the pore, and ④ is the nano-silicon particle.

[0096] Example 2

[0097] The porous nano-silicon carbon composite material coated with a carbon layer was prepared by the same method as in Example 1, except that the maximum carbonization temperature of the phenolic resin was 700 °C, and the porous nano-silicon carbon composite material coated with a carbon layer was obtained, denoted as Si@PF@CTP-700 °C.

[0098] Example 3

[0099] The porous nano-silicon carbon composite material coated with a carbon layer was prepared by the same method as in Example 1, except that the maximum carbonization temperature of the phenolic resin was 900 °C, and the porous nano-silicon carbon composite material coated with a carbon layer was obtained, denoted as Si@PF@CTP-900 °C.

[0100] Example 4

[0101] Compared with Example 1, the difference is that only steps (1) and (2) are included to prepare the porous nano-silicon carbon, denoted as Si@PF.

[0102] Comparative Example 1

[0103] Directly use commercially purchased nano-silicon carbon for testing and comparison.

[0104] As Figure 3 shown, from the SEM image of the nano-silicon carbon Si@PF prepared in Example 4, it can be seen that it has a porous structure, uniform particle size distribution, about 0.01 - 5 μm.

[0105] Figure 4 The morphological structure of the porous nano-silicon carbon composite material coated with a carbon layer (Si@PF@CTP-500 °C) is shown, and the existence of pores can be clearly seen inside the material.

[0106] As Figure 5 shown, obvious Si peaks and C peaks can be observed from the XRD pattern of the porous nano-silicon carbon composite material coated with a carbon layer.

[0107] From the charge-discharge curves ( Figure 6 ) and cycle test curves ( Figure 7 ) of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2, it can be seen that the porous nano-silicon carbon composite material electrode coated with a carbon layer of carbonized coal tar pitch has better initial Coulomb efficiency and cycle Coulomb than the porous nano-silicon carbon electrode without carbon coating. The porous nano-silicon carbon composite material (Si@PF@CTP-700 °C) coated with a carbon layer using a phenolic resin carbonization temperature of 700 °C has the best cycle performance and the highest specific capacity, and the corresponding nano-silicon dispersion structure, carbonization degree and thickness of the coating layer have the optimal performance.

[0108] The specific electrochemical performance data are shown in Table 1.

[0109] Table 1

[0110]

[0111] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a carbon-coated porous nano silicon-carbon composite material, characterized in that It includes the following steps: S1. Disperse nano-silicon and phenolic resin in ethanol respectively to obtain a nano-silicon slurry and a phenolic resin solution, mix and stir them to form a mixed slurry; S2. Spray-dry the mixed slurry to disperse nano-silicon particles in the phenolic resin and obtain a mixed powder; S3. Conduct a first carbonization treatment on the mixed powder in an inert atmosphere to obtain nano-silicon carbide with a porous structure; S4. Add coal tar pitch to a solvent and stir, then add the nano-silicon carbide with a porous structure and stir to dissolve it, conduct ball milling and mixing, and then conduct a second carbonization treatment to obtain the porous nano-silicon carbide composite material with a carbon-coated layer; In step S3, the step of conducting the first carbonization treatment on the mixed powder in an inert atmosphere specifically includes: placing the mixed powder in a tubular furnace into which an inert gas is introduced, and the heating method is as follows: Raise the temperature from room temperature to a first temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h; Raise the temperature from the first temperature to a second temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h; Raise the temperature from the second temperature to a third temperature at a rate of 1 - 5 °C / min and keep it warm for 0.5 - 2 h; Raise the temperature from the third temperature to a first carbonization temperature at a rate of 3 - 10 °C / min and keep it warm for 0.5 - 2 h; Among them, the first temperature is 80 - 120 °C, the second temperature is 100 - 140 °C, the third temperature is 120 - 180 °C, and the third temperature > the second temperature > the first temperature; The first carbonization temperature is 500 - 700 °C; In step S4, the heating method of the second carbonization treatment is as follows: Raise the temperature from room temperature to a fourth temperature at a heating rate of 5 - 30 °C / min; Raise the temperature from the fourth temperature to a second carbonization temperature at a heating rate of 5 - 30 °C / min and keep it warm for 6 h; Among them, the fourth temperature is 400 - 600 °C; The second carbonization temperature is 800 - 1000 °C; In step S1, the particle size of the nano-silicon is 10 - 200 nm; the mass ratio of the nano-silicon to the phenolic resin is (1:3) - (3:1); In step S2, the process conditions of the spray drying are: the inlet temperature of the spray drying is 100 - 200 °C, the outlet temperature is 50 - 150 °C, and the spray drying time is 0.5 - 5 h; In step S4, the ratio of the mass of the coal tar pitch to the sum of the masses of the nano-silicon and the phenolic resin is 1:(30 - 150); and / or the solvent is ethanol or toluene.

2. The preparation method of the carbon-coated porous nano silicon-carbon composite material according to claim 1, characterized in that, In step S4, the parameter conditions of the ball milling and mixing are: The mass ratio of the ball to the material is (1:2) - (2:1); The forward rotation speed is 300 - 700 rpm and the forward rotation time is 15 - 60 min; The reverse rotation speed is 300 - 700 rpm and the reverse rotation time is 15 - 60 min.

3. A carbon-coated porous nano-silicon carbon composite material, characterized in that, It is prepared by using the preparation method of the porous nano-silicon carbide composite material with a carbon-coated layer described in any one of claims 1 - 2; the particle size of the porous nano-silicon carbide composite material with a carbon-coated layer is 0.1 - 10 μm.

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