Porous structure silicon-carbon composite material and preparation method thereof

Abstract

The invention relates to a silicon-carbon composite material with a porous structure and a preparation method thereof, and the silicon-carbon composite material with the porous structure comprises an N / P co-doped porous carbon skeleton with micropore, mesopore and macropore channel networks, and amorphous or low-crystalline nanometer silicon particles which are uniformly loaded in the porous carbon skeleton and have the average particle size of 15-40nm, the mass percent of silicon in the composite material is 40-60%, and good interface bonding is formed between silicon and carbon. The preparation method mainly comprises the following steps: firstly, preparing an N / P co-doped porous carbon skeleton through a template method in combination with high-temperature carbonization and N / P source co-pyrolysis; and hydrolyzing an organic silicon source in the carbon skeleton to form silicon dioxide, and performing low-temperature metal thermal in-situ reduction to obtain the nano-silicon loaded composite material. Through a unique porous carbon skeleton design and a precise in-situ composite strategy of nano silicon, the prepared material shows high specific capacity, high initial coulombic efficiency and excellent cycling stability and rate capability when being used as a negative electrode of a lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, and particularly relates to a porous silicon-carbon composite material and a preparation method thereof. Background Art

[0002] With the profound changes in the global energy structure, the new energy industry represented by electric vehicles, portable electronic devices and large-scale energy storage systems has developed rapidly. Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and energy storage systems due to their advantages such as high energy density and long cycle life.

[0003] Currently, commercial lithium-ion batteries primarily use graphite as their anode material. However, graphite's low theoretical specific capacity makes it difficult to meet the growing demand for energy density. Silicon, due to its extremely high theoretical specific capacity, is considered a promising next-generation anode material. However, silicon's significant volume expansion during charge and discharge can lead to material pulverization, electrode structural damage, and SEI membrane instability, severely restricting its commercial application.

[0004] To solve the above problems, compounding silicon with carbon materials and designing porous structures is a current research hotspot. For example, although silicon-carbon materials with certain properties can be prepared by depositing silicon on a porous carbon skeleton using chemical vapor deposition, they usually face problems such as difficulty in controlling the uniformity of silicon deposition, high equipment costs, and stringent requirements on carbon carriers. Under high silicon loading, the cyclic stability and first coulombic efficiency of the material still have room for improvement. For another example, the template method is used to prepare porous silicon-carbon materials. Although the pore structure is highly designable, the process is often more complicated. Impurities may be introduced if the template is not removed thoroughly, and the cost of some template agents is relatively high, which is not conducive to large-scale production. In addition, the use of biomass (such as rice husks) to prepare porous silicon-carbon materials, although the cost is low, still faces challenges in structural uniformity, impurity control and batch stability of performance.

[0005] In summary, the existing technology still has many bottlenecks in how to economically and efficiently prepare porous silicon-carbon composite materials with high silicon content, high first coulombic efficiency, excellent cycle stability and good rate performance. In particular, further innovation and breakthroughs are needed in the fine structural regulation of the porous carbon skeleton, the uniform and controllable loading of nanosilicon and the strengthening of its interface with carbon. Summary of the Invention

[0006] The purpose of the present invention is to provide a porous structure silicon-carbon composite material and a preparation method thereof, which is intended to significantly improve its comprehensive electrochemical performance at high silicon content, especially cycle life, first coulombic efficiency and rate performance.

[0007] The purpose of the present invention can be achieved through the following technical solutions: A porous silicon-carbon composite material comprising an N / P co-doped porous carbon skeleton, nano-silicon particles, and an interface bonding layer disposed between the carbon skeleton and the nano-silicon particles; Wherein, in the N / P co-doped porous carbon skeleton, the mass percentage of nitrogen element is 0.5%-3%, and the mass percentage of phosphorus element is 0.5%-2%; The nano-silicon particles are loaded on the inner wall of the pores of the N / P co-doped porous carbon skeleton or embedded in the skeleton; the total mass percentage of the nano-silicon in the composite material is 40%-60%.

[0008] In this technical solution, there is a small amount of SiC transition layer formed by in-situ reaction between nano-silicon and N / P co-doped carbon skeleton, and / or chemical adsorption or weak chemical bonding formed by N, P doping sites and silicon surface to enhance the interface bonding force.

[0009] Preferably, the mass percentage of the N / P co-doped porous carbon skeleton in the composite material is 35%-55%.

[0010] Furthermore, the mass percentage of the N element and the P element in the N / P co-doped porous carbon skeleton in the composite material is 1%-5%.

[0011] As a preferred technical solution of the present invention, nano-silicon particles are dispersed on the inner wall of the carbon skeleton pores or embedded in the carbon skeleton in an amorphous or low-crystalline state.

[0012] In this technical solution, amorphous / low-crystalline silicon has better deformation ability than crystalline silicon.

[0013] As a preferred technical solution of the present invention, the average particle size of the nanosilicon particles is 15-40 nm.

[0014] As a preferred technical solution of the present invention, the carbon skeleton has a three-dimensional interconnected pore network composed of micropores, mesopores and macropores, the pore diameter of the micropores is less than 2nm; the pore diameter of the mesopores is 2-50nm; and the pore diameter of the macropores is greater than 50nm.

[0015] As a preferred technical solution of the present invention, the specific surface area of ​​the N / P co-doped porous carbon skeleton is 300-800 m² / g, and the total pore volume is 0.4-1.2 cm³ / g.

[0016] As a preferred technical solution of the present invention, the interface bonding layer is an in-situ formed SiC transition layer, and / or a chemical adsorption formed by N and P doping sites and the silicon surface.

[0017] As a preferred technical solution of the present invention, the outer surface of the composite material is covered with an amorphous carbon thin layer, and the thickness of the amorphous carbon thin layer is 5-10 nm.

[0018] Preferably, the mass percentage of the amorphous carbon layer in the composite material is 2%-5%.

[0019] A method for preparing the porous silicon-carbon composite material as described above comprises the following steps: S1. providing a carbon precursor, a sacrificial nano-template, a nitrogen source, and a phosphorus source, mixing them, and then performing pre-carbonization, high-temperature carbonization, and N / P co-doping treatment under an inert atmosphere; S2, removing the sacrificial nano-template by etching to obtain an N / P co-doped porous carbon framework; S3, contacting the N / P co-doped porous carbon skeleton with an organosilicon source, hydrolyzing the organosilicon source and forming a silicon dioxide layer in the pores and / or on the surface of the carbon skeleton; S4. The carbon skeleton loaded with silicon dioxide is mixed with a metal reducing agent, and heat-treated in an inert atmosphere or under vacuum conditions to reduce the silicon dioxide to nano-silicon in situ, and then washed and purified to obtain a composite material of N / P co-doped porous carbon loaded with nano-silicon.

[0020] Preferably, in step S1, the carbon precursor is modified phenolic resin or polyacrylonitrile, the sacrificial nano-template is silica nanospheres and / or calcium carbonate nanoparticles, the nitrogen source is melamine, and the phosphorus source is red phosphorus.

[0021] Furthermore, in step S1, the inert atmosphere is nitrogen or argon. The pre-carbonization temperature is 300-500°C for 1-2 hours. The high-temperature carbonization temperature is 700-900°C for 2-4 hours, and N / P co-doping is performed simultaneously. The heating rate from pre-carbonization to high-temperature carbonization is 2-5°C / min.

[0022] During the carbonization process, melamine was introduced as a nitrogen source and red phosphorus as a phosphorus source, and in-situ co-doping of N and P elements in the carbon skeleton was achieved through high-temperature pyrolysis, which simplified the process.

[0023] By controlling the pre-polymerization conditions before carbonization and the amount and particle size of the template agent added, the porosity and pore size of the carbon skeleton can be regulated. Specifically, the carbon precursor can produce a microporous structure under carbonization conditions, with a pore size of <2nm. The smaller-sized template agent loaded on the carbon precursor can generate a mesoporous structure after removal or activation, with a pore size of 2-50nm. The larger-sized template agent or particle accumulation loaded on the carbon precursor can generate a macroporous structure with a pore size of >50nm, thereby forming a three-dimensional interconnected pore network with micropores, mesopores and macropores.

[0024] Preferably, in step S2, the etching agent used is HF solution and / or dilute hydrochloric acid; further, HF solution is used to remove the silica template, and dilute hydrochloric acid is used to remove the calcium carbonate template. After etching, the solution is washed to neutrality and then dried to obtain an N / P co-doped porous carbon framework.

[0025] This technical solution achieves the initial construction of the pore structure through the synergistic effect of the template and the carbon precursor, combined with subsequent etching.

[0026] Preferably, after step S2 and before step S3, the porous carbon after the template is removed is activated to further optimize the microporous structure and specific surface area.

[0027] Preferably, the activation treatment is specifically to use carbon dioxide or water vapor for short-time activation at 600-750° C. The activation energy can be used to further optimize the pore structure without destroying the overall skeleton.

[0028] Preferably, in step S3, the organic silicon source is tetraethoxysilane (TEOS).

[0029] Preferably, the specific operation of step S3 is: dispersing the prepared N / P-doped porous carbon skeleton in an ethanol / water mixed solvent, adding an organosilicon source and a small amount of acidic or alkaline catalyst, and then stirring at 40-70°C to hydrolyze the organosilicon source and form a silica sol-gel layer in the pores and on the surface of the carbon skeleton.

[0030] Preferably, in step S4, the metal reducing agent is magnesium powder or aluminum powder, and the heat treatment temperature is 600-750°C.

[0031] Preferably, the specific operation of step S4 is: drying the carbon skeleton loaded with silica to remove the solvent, and then mixing it with a metal reducing agent; then heat-treating the mixture in an inert atmosphere or under vacuum to reduce the silica to nano-silicon in situ; after the reduced product is cooled, washing with dilute acid to remove the generated metal oxides and unreacted metals, and then washing with deionized water to neutrality, and drying to obtain a composite material of N / P-doped porous carbon loaded with nano-silicon.

[0032] Preferably, in step S4, the heat treatment temperature is 600-750° C. and the time is 2-5 hours.

[0033] Specifically, the present technical solution adopts a liquid-phase impregnation-in-situ chemical reduction method, with tetraethoxysilane as the silicon source, and in the presence of an N / P-doped porous carbon skeleton, controls the hydrolysis-condensation to form a silica nanosol, and then uses magnesium powder or aluminum powder in situ for thermal reduction at 600-750°C to obtain amorphous or low-crystallinity nano-silicon particles with an average particle size of 15-40nm, which are uniformly dispersed on the inner wall of the carbon skeleton pores or embedded in the carbon skeleton.

[0034] Specifically, the hydrolysis product of tetraethoxysilane can penetrate well into the interior of porous carbon, and the subsequent low-temperature thermal reduction is conducive to the formation of small-sized and evenly dispersed nano-silicon, and the formation of favorable bonds such as SiC or Si-OC at the interface.

[0035] Compared to traditional multi-step high-temperature CVD or complex hard template methods, the silicon loading method of the present invention uses liquid-phase impregnation and low-temperature in-situ reduction, which is relatively mild and requires less equipment. N / P doping and carbonization are performed simultaneously, simplifying the process.

[0036] Furthermore, in step S4, during the magnesium / aluminothermic reduction process, some silicon reacts with the carbon skeleton at high temperature, forming a small amount of SiC interface transition layer in situ. Simultaneously, the active sites on the N- and P-doped carbon surfaces can form strong chemical adsorption or weak chemical bonds with the surface of the nano-silicon particles, jointly strengthening the bond between the silicon and carbon skeleton and effectively preventing electrochemical "islanding" of the silicon particles during cycling.

[0037] Preferably, after step S4, the method further comprises step S5: coating the composite material obtained in step S4 with an amorphous carbon layer having a thickness of 5-10 nm on its surface by low-temperature chemical vapor deposition or liquid phase impregnation-low-temperature pyrolysis.

[0038] Furthermore, in step S5, the specific operation of the low-temperature chemical vapor deposition method is: placing the silicon-carbon composite material obtained in step S4 in a tube furnace, introducing carbon-containing gas under an inert atmosphere, and performing chemical vapor deposition at 350-450°C for 0.5-2 hours to form a thin amorphous carbon coating layer.

[0039] Preferably, the carbon-containing gas is acetylene gas, the flow rate of which is controlled at 10-50 sccm, and can be diluted with Ar.

[0040] Furthermore, in step S5, the specific operation of the liquid phase impregnation-low temperature pyrolysis method is: dispersing the composite material in a solution containing glucose, drying after impregnation, and then heating to 500-600°C under an inert atmosphere and performing low temperature pyrolysis to form a carbon coating layer.

[0041] Among them, the use of low-temperature coating technology can avoid the negative effects of high temperature on the internal nano-silicon structure, such as excessive crystallization or agglomeration. At the same time, the flexible carbon layer formed is more conducive to adapting to the volume changes of silicon.

[0042] The amorphous carbon thin layer can physically isolate the internal active silicon from direct excessive contact with the electrolyte, helping to stabilize the SEI film; buffer the mechanical stress between particles, further improving the overall electronic conductivity of the composite material particles and improving the integrity of the electrode.

[0043] Preferably, the porous structure silicon-carbon composite material of the present technical solution can be applied to the field of preparing negative electrode materials for lithium-ion batteries, wherein the carbon material can significantly improve the conductivity of the composite material and act as a buffer matrix to alleviate the volume expansion of silicon; and the porous structure can provide reserved space for the volume change of silicon, buffer the volume expansion, shorten the lithium ion diffusion path, and promote ion transport. Its high specific surface area can increase the active surface and load active substances, so as to evenly disperse and anchor the nano-silicon particles on its skeleton, prevent the silicon particles from agglomerating, and further stabilize the electrode structure.

[0044] Beneficial effects of the present invention: (1) The present invention uses a composite of a modified phenolic resin or polyacrylonitrile with specific functional groups and a sacrificial nano-template as a carbon source and pore-forming agent. Phenolic resin / polyacrylonitrile is used to provide a carbon skeleton, which contains nitrogen and oxygen functional groups, which are conducive to subsequent heteroatom doping and bonding with silicon; the sacrificial template is used to form a macroporous or mesoporous structure through selective etching after carbonization. During the carbonization process, nitrogen and phosphorus sources are introduced. N doping can improve the electronic conductivity and surface polarity of the carbon material and increase the lithium storage active sites; P doping can further improve the conductivity and may form a P-Si bond with silicon to enhance the interface bonding. The synergistic effect of N / P co-doping can optimize the formation of the SEI film and enhance the anchoring effect on silicon nanoparticles, thereby jointly constructing an efficient electronic conductive network.

[0045] (2) The present invention forms three-dimensional interconnected pores by controlling the pre-polymerization conditions before carbonization and the amount and particle size of the template agent added. Among them, the macropores are fast ion channels, the mesopores promote electrolyte infiltration, and the micropores provide active sites. Together with the highly conductive N / P-doped carbon skeleton, they construct efficient lithium ion and electron dual transport channels, thereby optimizing the lithium ion transport path; on the other hand, the porous structure provides sufficient buffer space for the volume expansion of silicon, effectively buffering the huge volume expansion of silicon, and the strengthened Si-C interface effectively inhibits the pulverization and shedding of silicon particles. N / P doping and the optional outer carbon layer help to form a stable SEI film, reducing the loss of active lithium, and providing a feasible technical approach for the development of the next generation of high-performance, low-cost lithium-ion battery negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a scanning electron microscope (SEM) image of the porous silicon-carbon composite material of the present invention. DETAILED DESCRIPTION

[0047] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0048] Example 1 A porous silicon-carbon composite material, the preparation method of which comprises the following steps: S1. Weigh 10 g of modified phenolic resin and dissolve it in 50 mL of ethanol. Add 2 g of silica nanospheres with an average particle size of 80 nm as a macroporous template, 1 g of melamine as a nitrogen source, and 0.5 g of red phosphorus as a phosphorus source. Ultrasonicate and disperse for 30 minutes until uniform. Rotary evaporate to remove the ethanol to obtain a precursor mixture.

[0049] The mixture was placed in a tube furnace, and then under nitrogen atmosphere protection, the temperature was raised to 400°C at a rate of 3°C / min and kept at this temperature for 1 hour for pre-carbonization; then the temperature was raised to 800°C at a rate of 5°C / min and kept at this temperature for 3 hours for high-temperature carbonization and N / P co-doping, and then naturally cooled to room temperature.

[0050] S2. The product obtained in step S1 was etched with a 10 wt % HF aqueous solution at room temperature for 24 hours with stirring to remove the silica template, and then washed with deionized water until neutral, and vacuum dried at 80° C. for 12 hours to obtain an N / P co-doped porous carbon skeleton (denoted as NP-HPC).

[0051] Elemental analysis revealed that the nitrogen content of NP-HPC was approximately 1.8wt%, and the phosphorus content was approximately 0.9wt%. BET analysis revealed a surface area of ​​550m² / g and a total pore volume of 0.75cm³ / g. The pore size distribution showed the presence of mesopores ranging from approximately 5-15nm and macropores ranging from approximately 70-90nm.

[0052] S3. Disperse 2 g of the NP-HPC prepared in step S2 in 100 mL of anhydrous ethanol, add 6 mL of tetraethoxysilane and 0.5 mL of 1 M HCl aqueous solution as catalyst, and stir at 60° C. for 6 hours. After the reaction, collect the solid by centrifugation and vacuum dry at 80° C. for 12 hours to obtain silica-loaded NP-HPC (silica@NP-HPC).

[0053] S4. Weigh the dried silica@NP-HPC and 0.8g of magnesium powder with an average particle size of 1-5 microns, wherein the molar ratio of magnesium to the expected silica is about 2.2:1. Grind and mix thoroughly in a mortar, then place the mixture in a quartz boat, put it into a tube furnace, and under the protection of an argon atmosphere, heat it to 700°C at a rate of 5°C / min and keep it warm for 3 hours for magnesium thermal reduction. After natural cooling, the product is stirred and washed with 2MHCl solution for 6 hours to remove magnesium oxide and unreacted magnesium, then washed with deionized water until neutral, and vacuum dried at 80°C for 12 hours to obtain an N / P co-doped porous carbon-loaded nanosilicon composite material (denoted as Si@NP-HPC).

[0054] like Figure 1This is a scanning electron microscope (SEM) image of the Si@NP-HPC obtained in this example, which shows a complex three-dimensional network porous structure.

[0055] Example 2 The difference between this embodiment and embodiment 1 is that this embodiment further includes step S5. The specific operation of step S5 is: S5. Place 1 g of the Si@NP-HPC prepared in step S4 in a fluidized bed reactor in a tubular furnace and heat to 400°C under an argon atmosphere. Then, introduce a mixture of 80 sccm of argon and 20 sccm of acetylene. After reacting for 1 hour, stop the acetylene flow and allow the mixture to cool to room temperature under an argon atmosphere. This yields an N / P co-doped porous carbon@nanosilicon composite material coated with flexible carbon (denoted as C-Si@NP-HPC).

[0056] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S1 of this comparative example, melamine is not added, and the remaining components, preparation steps and parameters are the same.

[0057] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S1 of this comparative example, red phosphorus is not added, and the remaining components, preparation steps and parameters are the same.

[0058] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S3 of this comparative example, the volume of tetraethoxysilane is 1 mL, and the other components, preparation steps and parameters are the same.

[0059] Comparative Example 4 In this comparative example, commercial micron silicon powder (average particle size 3 μm) was directly mixed with conductive carbon black and PVDF binder in a mass ratio of 8:1:1 to prepare an electrode.

[0060] The electrochemical performance tests of Examples 1-2 and Comparative Examples 1-4 were conducted as follows: The products of Examples 1-2 and Comparative Examples 1-4 were used as active materials, numbered 1-6, and mixed with conductive carbon black and sodium carboxymethyl cellulose (CMC) / styrene-butadiene rubber (SBR) binder (CMC:SBR = 1:1 by mass ratio) at a mass ratio of 80:10:10 in deionized water to form a slurry. The slurry was evenly coated on a copper foil current collector, and the active material surface density was approximately 1.0-1.2 mg / cm 2 After drying in a vacuum oven at 80°C for 12 hours, the electrodes were punched into circular pieces with a diameter of 12 mm.

[0061] Metal lithium sheets were used as counter and reference electrodes, Celgard 2400 was used as the separator, 1 M LiPF6 was dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1), and 5 wt% fluoroethylene carbonate was added as an electrolyte additive. The cells were assembled into CR2032 button cells in an argon-filled glove box.

[0062] (1) Constant current charge and discharge tests were performed at room temperature using the LAND battery test system with a voltage window of 0.01-1.5V (vs. Li / Li + ).

[0063] (2) The first cycle current density is 0.05C, and the subsequent cycle current densities are 0.1C, 0.5C, 1C, 3C, and 5C for rate performance testing. After that, a long cycle performance test is performed at a current density of 1C for 500 times.

[0064] The test results are shown in Table 1.

[0065] Table 1 As can be seen from the test results in Table 1, the test results of Examples 1 and 2 are significantly better than those of Comparative Examples 1 to 4. This indicates that the silicon-carbon composite material of the present invention exhibits excellent performance in terms of first coulombic efficiency, rate capability, and cycle stability. This is attributed to the unique porous structure of the silicon-carbon composite material of the present invention, the additional lithium storage sites and improved conductivity provided by the N / P co-doped carbon skeleton, and the uniform dispersion of nano-silicon and the stable Si-C interface, thereby achieving a significant improvement in the overall electrochemical performance.

[0066] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A porous silicon-carbon composite material, characterized in that: It includes an N / P co-doped porous carbon skeleton, nano-silicon particles and an interface bonding layer arranged between the carbon skeleton and the nano-silicon particles; Wherein, in the N / P co-doped porous carbon skeleton, the mass percentage of nitrogen element is 0.5%-3%, and the mass percentage of phosphorus element is 0.5%-2%; The nano-silicon particles are loaded on the inner wall of the pores of the N / P co-doped porous carbon skeleton or embedded in the skeleton; the total mass percentage of the nano-silicon in the composite material is 40%-60%.

2. The porous silicon-carbon composite material according to claim 1, characterized in that: The nano silicon particles are dispersed on the inner wall of the carbon skeleton pores or embedded in the carbon skeleton in an amorphous or low crystalline state.

3. The porous silicon-carbon composite material according to claim 1, characterized in that: The average particle size of the nanosilicon particles is 15-40 nm.

4. The porous silicon-carbon composite material according to claim 1, characterized in that: The carbon skeleton has a three-dimensional interconnected pore network consisting of micropores, mesopores and macropores. The pore diameter of the micropores is less than 2nm; the pore diameter of the mesopores is 2-50nm; and the pore diameter of the macropores is greater than 50nm.

5. The porous silicon-carbon composite material according to claim 1, characterized in that: The N / P co-doped porous carbon skeleton has a specific surface area of ​​300-800 m² / g and a total pore volume of 0.4-1.2 cm³ / g.

6. The porous silicon-carbon composite material according to claim 1, characterized in that: The interface bonding layer is an in-situ formed SiC transition layer and / or is formed by chemical adsorption between N and P doping sites and the silicon surface.

7. The porous silicon-carbon composite material according to claim 1, characterized in that: The outer surface of the composite material is covered with an amorphous carbon thin layer, and the thickness of the amorphous carbon thin layer is 5-10 nm.

8. A method for preparing a porous silicon-carbon composite material according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: S1. providing a carbon precursor, a sacrificial nano-template, a nitrogen source, and a phosphorus source, mixing them, and then performing pre-carbonization, high-temperature carbonization, and N / P co-doping treatment under an inert atmosphere; S2, removing the sacrificial nano-template by etching to obtain an N / P co-doped porous carbon framework; S3, contacting the N / P co-doped porous carbon skeleton with an organosilicon source, hydrolyzing the organosilicon source and forming a silicon dioxide layer in the pores and / or on the surface of the carbon skeleton; S4. The carbon skeleton loaded with silicon dioxide is mixed with a metal reducing agent, and heat-treated in an inert atmosphere or under vacuum conditions to reduce the silicon dioxide to nano-silicon in situ, and then washed and purified to obtain a composite material of N / P co-doped porous carbon loaded with nano-silicon.

9. The preparation method according to claim 8, characterized in that In step S1, the carbon precursor is a modified phenolic resin or polyacrylonitrile, the sacrificial nano-template is silica nanospheres and / or calcium carbonate nanoparticles, the nitrogen source is melamine, and the phosphorus source is red phosphorus; After step S2 and before step S3, the porous carbon after the template is removed is activated to further optimize the microporous structure and specific surface area; In step S3, the organosilicon source is tetraethoxysilane (TEOS); In step S4, the metal reducing agent is magnesium powder or aluminum powder, and the heat treatment temperature is 600-750°C.

10. The preparation method according to claim 8, characterized in that After step S4, the method further includes step S5: coating the composite material obtained in step S4 with an amorphous carbon layer having a thickness of 5-10 nm on its surface by low-temperature chemical vapor deposition or liquid phase impregnation-low-temperature pyrolysis.

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