CN106099113A - A kind of nucleocapsid structure Si-C composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a silicon-carbon composite material with a core-shell structure and a preparation method thereof. The composite material has a core-shell structure; the core-shell structure includes an outer shell composed of a carbon layer and a core composed of porous nano-silicon; There is a gap layer between the outer shell and the inner core; the preparation method is to carry out magnesium thermal reduction reaction on silica particles through magnesium powder, and the reduction product is coated with organic polymer carbon source in situ, then carbonized, and the carbonized product is made of hydrogen fluorine Acid corrosion, that is, silicon-carbon composite material, the silicon-carbon composite material has good stability, and can well buffer the volume expansion of silicon, improve the conductivity of the material, thereby ensuring the cycle stability of the electrode; the preparation process of the silicon-carbon composite material is simple, The source of raw materials is extensive and suitable for industrialized production.

Description

A kind of core-shell structure silicon-carbon composite material and preparation method thereof

technical field

The invention relates to a preparation method of a lithium-ion battery negative electrode material, in particular to a silicon-carbon composite material with a core-shell structure and a preparation method thereof, belonging to the technical field of lithium-ion batteries.

Background technique

Since the beginning of the 21st century, with the development of society and the advancement of technology, electronic products, electric vehicles and energy storage power stations increasingly require lithium-ion batteries with high energy density and long life. However, graphite-based negative electrode materials are widely used in commercial lithium-ion batteries at present, and their theoretical capacity is low (372mAh/g), which is difficult to meet the demand. As an anode material, silicon has a very high theoretical specific capacity (4200mAh/g), which has attracted extensive attention from researchers. During the charge and discharge process of silicon, the deintercalation of lithium ions will lead to a huge volume change, resulting in particle breakage and pulverization, causing the silicon active material to fall off from the current collector, eventually leading to the destruction of the internal structure of the electrode, which in turn affects the Electrochemical performance of the battery. Through research, it is found that reducing the size of silicon materials to the nanometer level can effectively alleviate its volume change during charge and discharge, and carbon coating can also improve the conductivity of the material and inhibit volume expansion. The excellent properties of silicon-carbon composite materials make them promising to replace graphite-based anode materials. Large-scale, low-cost preparation of structurally stable nano-silicon-carbon composite materials is the basis for their commercial application.

Wang et al. used resorcinol-formaldehyde as a carbon source, added nano-silicon materials to obtain silicon-carbon aerogels, and obtained carbon-coated silicon-based materials after sintering [G.X.Wang, et al.Electrochemistry Communications, 2004,6(7) :689-692], but the coated carbon layer is easily damaged after repeated cycles, which is difficult to meet the needs of practical applications. Patent CN102623680A discloses a method for preparing a silicon-carbon composite negative electrode material with a three-dimensional reserved pore structure. This method removes the silicon dioxide coated on the surface of silicon particles in the carbon matrix, thereby obtaining Three-dimensional expansion space is reserved. Although this method effectively improves the charge-discharge cycle performance of the material, it needs to first generate silicon dioxide and then remove the silicon dioxide. The complicated steps are not conducive to large-scale production, and it does not solve the low-cost preparation of nano-silicon. The problem. Patent CN 104979539A uses zinc oxide as a template, deposits a layer of silicon dioxide and a carbon layer on the template respectively, and obtains a silicon-carbon nanorod composite material with a hollow structure after magnesia thermal reduction. This method can also obtain better electrochemical performance , but the preparation and etching of the template increases the preparation cost, and the CVD method used for carbon coating is complicated, which is not conducive to large-scale production.

The preparation of nano-silicon by the reduction reaction of silica and magnesium powder has the advantages of simple method and low cost, and is considered to be one of the methods suitable for large-scale application at present. However, in the process of preparing silicon-carbon composite materials, since magnesia thermal reduction is an exothermic reaction, local heat accumulation will lead to side reactions in the system and generate silicon carbide impurity phases. Silicon carbide has no reactivity with lithium, which not only leads to a decrease in the specific capacity of the material, but also affects the interfacial transfer of lithium ions in the electrode material. This greatly reduces the specific capacity and rate capability of the prepared materials. How to prepare silicon-carbon composite materials with stable structure by magnesia thermal reduction is of great significance to promote the industrial application of silicon-carbon anode materials.

Contents of the invention

Aiming at the shortcomings of the existing silicon-carbon composite materials for lithium-ion batteries, the purpose of the present invention is to provide a silicon-carbon composite material with a special core-shell structure, which has good stability and can well buffer During the charge and discharge process, the volume of silicon expands, which improves the conductivity of the material, thereby ensuring the cycle stability of the electrode.

Another object of the present invention is to provide a simple, low-cost, and side-reaction-free method for preparing the silicon-carbon composite material, which can be produced on a large scale.

In order to achieve the above technical purpose, the present invention provides a silicon-carbon composite material with a core-shell structure, which has a core-shell structure; the core-shell structure includes a shell made of carbon layers and a porous nano-silicon Inner core; there is a gap layer between the outer shell and the inner core.

The silicon-carbon composite material provided by the present invention has a special core-shell structure, the core of which is porous nano-silicon, and the shell is a carbon layer, especially there is a gap layer between the core and the shell. The carbon layer can not only improve the conductivity of the material, but also prevent the silicon nuclei from breaking and scattering, ensuring the stability of the material structure, while the interstitial layer provides a buffer space for the volume expansion of silicon during the charging and discharging process of the battery, effectively preventing the composite material from falling apart during charging and discharging. During the discharge process, it is broken and pulverized due to the volume change, so as to ensure the cycle stability of the electrode.

In a preferred solution, the size of the inner core is 10nm-10μm.

In a preferred solution, the thickness of the shell is 1-200 nm.

The present invention also provides a method for preparing the silicon-carbon composite material with a core-shell structure, the method comprising the following steps:

1) SiO2 particles undergo magnesium thermal reduction reaction through magnesium powder to obtain Si@SiO ₂ intermediate;

2) The Si@SiO ₂ intermediate is coated in-situ by an organic polymer carbon source, and then carbonized to obtain a C@Si@SiO ₂ intermediate;

3) The C@Si@SiO ₂ intermediate is corroded with hydrofluoric acid to obtain it.

In the technical solution of the present invention, the silicon dioxide is partially reduced to generate silicon by the magnesia thermal reduction method, and the silicon-coated silicon dioxide intermediate Si@SiO ₂ is mainly obtained; ₂ Prepare a carbon layer coating layer on the surface, and then use hydrofluoric acid to selectively remove silicon dioxide and partially reduced nano-silicon to obtain a carbon layer-coated silicon composite material C@Si. The removal of silicon dioxide and part of silicon not only leaves a corresponding space volume between the carbon layer and the silicon core, but also generates a porous nano-silicon core. By controlling the size of the void layer, the freedom of silicon particles in the carbon layer can be guaranteed. expand without destroying the overall structure.

In the preferred solution, in 1), after mixing the silica particles and magnesium powder evenly, place them in a closed environment filled with a protective atmosphere, raise the temperature to 600-800°C at a heating rate of 1-20°C/min, and carry out the reduction reaction 1～12h, the Si@SiO ₂ intermediate is obtained. The preferred conditions for the magnesia thermal reduction can well control the degree of magnesia thermal reduction, thereby realizing the control of the porous nano-silicon structure. In the process of magnestic reduction, not only the reaction of 2Mg+SiO ₂ →Si+2MgO, but also a series of reactions such as 2Mg+Si→Mg ₂ Si and Mg ₂ Si+SiO ₂ →2Si+2MgO occurred, so not only the two The surface of the silicon oxide is reduced to form silicon, and a small part of the interior of the silicon dioxide is also reduced to form silicon, so a porous nano-silicon core is formed in the subsequent hydrofluoric acid etching process; at the same time, the surface of the silicon dioxide is reduced The silicon particles are very small and highly active, and it is easy to react with hydrofluoric acid during hydrofluoric acid corrosion, forming a gap layer between the carbon shell and the porous nano-silicon core.

More preferably, the mass ratio of silicon dioxide to magnesium powder is 1:0.4-1:1.

In a more preferred solution, the particle size of the silicon dioxide particles is 10 nm to 10 μm.

In the preferred scheme, in 2), the Si@SiO ₂ intermediate and the organic polymer carbon source are dissolved in a solvent, and after mixing uniformly, they are stirred and evaporated to dryness, and the obtained solid mixture is ground and placed under a protective atmosphere. Raise the temperature to 600-1200°C at a heating rate of ~20°C/min, and perform carbonization for 1-12 hours to obtain a C@Si@SiO ₂ intermediate. Optimal in-situ coating and carbonization conditions can prepare a uniform carbon layer on the surface of the Si@SiO ₂ intermediate.

In a preferred solution, the mass ratio of the organic polymer carbon source to the Si@SiO ₂ intermediate is 100:1˜1:100.

In a preferred solution, the organic polymer carbon source is at least one of polyvinyl alcohol, polypropylene, pitch, phenolic resin, epoxy resin, glucose, sucrose and starch. The preferred organic polymer carbon source is a water-soluble polymer material, or a polymer material that is easily soluble in an organic solvent. These organic polymer carbon sources are easy to coat the Si@SiO ₂ intermediate in situ with the help of a solvent medium.

In a preferred solution, in 3), the C@Si@SiO ₂ intermediate is impregnated with hydrofluoric acid with a mass percent concentration of 1-40% for 0.01-6 hours.

More preferably, the protective atmosphere is at least one of nitrogen, argon and hydrogen.

The preparation method of the core-shell structure silicon-carbon composite material of the present invention comprises the following steps:

Step 1: Mix silica particles (particle size 10nm~10μm) and magnesium powder uniformly according to the mass ratio of 1:0.4~1:1, and place them in a closed environment full of protective atmosphere at 1~20℃/ The heating rate of min is raised to 600-800°C for 1-12 hours; after the reaction, the product is taken out, and the product is added to hydrochloric acid and/or sulfuric acid solution with a concentration of 0.5-4mol/L to wash for 1-24 hours, filtered and dried After that, the intermediate product Si@SiO ₂ is obtained;

Step 2: Dissolve the organic polymer carbon source and Si@SiO ₂ in the solvent at a mass ratio of 100:1 to 1:100, mix evenly, stir and evaporate the solution at 60 to 120°C, and grind the obtained mixture Under a protective atmosphere, raise the temperature to 600-1200°C at a rate of 1-20°C/min to react for 1-12 hours, and obtain carbon-coated C@Si@SiO ₂ after the reaction;

Step 3: Dissolve C@Si@SiO ₂ in a hydrofluoric acid solution with a concentration of 1-40wt% and soak for 0.01-6 hours. After removing the remaining SiO ₂ and a small amount of silicon, filter and wash to obtain the final product with a core-shell structure C@Si.

Compared with the prior art, the technical solution of the present invention has the following advantages:

1) The silicon-carbon composite material obtained by the technical solution of the present invention has a special core-shell structure, including a porous nano-silicon core and a carbon layer shell, especially a void layer between the core and the shell. The carbon layer can not only improve the conductivity of the material, but also prevent the silicon nuclei from breaking and scattering, ensuring the stability of the material structure, while the interstitial layer provides a buffer space for the volume expansion of silicon during the charging and discharging process of the battery, effectively preventing the composite material from falling apart during charging and discharging. During the discharge process, it is broken and pulverized due to the volume change, so as to ensure the cycle stability of the electrode.

2) In the technical solution of the present invention, in the process of preparing the silicon-carbon composite material, silicon dioxide is first reduced by magnesia, and then coated with carbon, which effectively avoids the generation of side reactants such as silicon carbide.

3) The technical solution of the present invention can realize the regulation of the size of the void layer in the silicon-carbon composite material and the regulation of the porous nano-silicon structure by controlling the degree of magnesium thermal reaction.

4) The technical solution of the present invention does not need to use nano-silicon as a raw material, has a wide source of raw materials, low cost, simple and controllable process, does not require expensive manufacturing equipment, is suitable for large-scale production, and has a good practical prospect.

Description of drawings

[Figure 1] The X-ray diffraction pattern of the reaction product prepared in Comparative Example 1: It can be seen from the figure that the material prepared by first coating carbon and then magnesia thermal reduction has an obvious miscellaneous peak at about 36°, indicating that the reaction produced Silicon carbide impurities.

[Figure 2] Transmission electron microscope image of the reaction product prepared in Comparative Example 2: It can be seen from the figure that the product obtained by treating with hydrochloric acid and hydrofluoric acid after magnesium thermal reduction has an obvious porous structure.

[Figure 3] is the X-ray diffraction pattern of the reaction product prepared in Example 1: it can be seen from the figure that there is no silicon carbide impurity component in the silicon-carbon composite material prepared by the technical solution of the present invention.

[Fig. 4] The transmission electron microscope image of the silicon dioxide precursor used in Example 1: It can be seen from the figure that the silicon dioxide before reduction is a smooth solid sphere.

[Figure 5] The transmission electron microscope image of the Si@SiO ₂ intermediate product prepared in Example 1: It can be seen from the figure that the intermediate product obtained by hydrochloric acid treatment after magnesia thermal reduction maintains the overall shape and does not have obvious pores structure.

[Figure 6] Transmission electron microscope image of the C@Si product prepared in Example 1: It can be seen from the figure that the silicon core is wrapped by a layer of amorphous carbon, and there is an obvious gap layer between the carbon shell and the silicon core.

[Fig. 7] The 50-time charge and discharge capacity diagram of the silicon-carbon composite material prepared in Example 1 when used as the negative electrode material of lithium-ion batteries: it can be seen from the figure that the first reversible specific capacity of the battery is 1791mAh/g, and the cycle is 50 The reversible specific capacity after the cycle is 1690mAh/g.

detailed description

The specific steps of the present invention are illustrated below through examples, but the scope of protection of the claims of the present invention is not limited by the examples.

The terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art.

The present invention will be further described in detail below in conjunction with specific examples and with reference to data. It should be understood that these examples are only for illustration of the present invention, but not to limit the scope of the present invention in any way.

In the following examples, various procedures and methods not described in detail are conventional methods well known in the art.

The present invention will be further described below in conjunction with specific examples.

Comparative example 1

Take 1g of silica balls with a diameter of about 250nm as a raw material, dissolve them in an ethanol solvent with a mass ratio of 1:1 with a phenolic resin, stir at 80°C until the ethanol is completely volatilized, grind the mixture finely, and place in an argon atmosphere. The temperature was raised to 800°C at a heating rate of 5°C/min for 2 hours. After the reaction, the obtained product C@SiO ₂ was mixed with 0.8g metal magnesium powder evenly, placed in a closed environment filled with argon, and heated to 700°C at a heating rate of 5°C/min for 6 hours. After the reaction, the product was taken out and dissolved in 1mol/L hydrochloric acid to react for 6h. After filtering and drying, it was dissolved in hydrofluoric acid with a mass fraction of 5% and reacted for 0.5 h, and the reaction product was obtained after filtering and drying. The X-ray diffraction pattern of the reaction product is shown in Figure 1, and the product contains a large amount of silicon carbide impurity components.

The prepared material, conductive carbon black, and sodium alginate were prepared into a slurry at a mass ratio of 8:1:1, coated on a copper foil, and dried at 60°C for 12 hours to make a negative electrode sheet for a lithium-ion battery. A coin-type lithium battery CR2025 was used as a simulated battery, a metal lithium sheet was used as a counter electrode, the electrolyte composition was 1MLiPF ₆ (ethylene carbonate:diethyl carbonate=1:1, v/v), the diaphragm was Celgard2400, and the battery was filled with argon. Assembled in the glove box. The prepared battery is charged and discharged at a current density of 100mA/g with a charging and discharging interval of 0.01-1.5V. The first reversible specific capacity of the battery is 546mAh/g, and the reversible specific capacity after 50 cycles is 308mAh/g.

Comparative example 2

Take 1g of silica balls with a diameter of about 250nm as raw materials, mix them with 0.8g of metal magnesium powder, place them in a closed environment filled with argon, and raise the temperature to 700°C at a heating rate of 5°C/min for 6 hours. After the reaction, the product was taken out and dissolved in 1mol/L hydrochloric acid to react for 6h. After filtering and drying, it was dissolved in hydrofluoric acid with a mass fraction of 5% and reacted for 0.5 h, and the reaction product was obtained after filtering, washing and drying. The transmission electron microscope image of the reaction product is shown in Figure 2, and there are a large number of holes in the product.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The test results show that the first reversible specific capacity of the battery is 2375mAh/g, and the reversible specific capacity after 50 cycles is 551mAh/g.

Example 1

Take 1g of silica balls with a diameter of about 250nm as raw materials, mix them with 0.8g of metal magnesium powder, place them in a closed environment filled with argon, and raise the temperature to 700°C at a heating rate of 5°C/min for 6 hours. After the reaction, the product was taken out and dissolved in 1mol/L hydrochloric acid to react for 6h. After filtering and drying, the intermediate product Si@SiO ₂ and phenolic resin obtained above were dissolved in ethanol solvent at a mass ratio of 1:1, stirred at 80°C until the ethanol was completely volatilized, and the mixture was finely ground and then placed in an argon atmosphere. The temperature was raised to 800°C at a heating rate of 5°C/min for 2 hours. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in 5% hydrofluoric acid and reacted for 0.5 h, filtered, washed and dried to obtain the reaction product C@Si. The X-ray diffraction pattern of the product C@Si is shown in Figure 3, the transmission electron microscope image of the silicon dioxide precursor used is shown in Figure 4, and the transmission electron microscope image of the obtained intermediate product Si@ _SiO2 is shown in Figure 5. The transmission electron microscope image of its product C@Si is shown in Figure 6. The diameter of the porous nano-silicon core of the obtained product is about 250nm, and the thickness of the carbon layer is about 10nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. As shown in Figure 7 is the charge and discharge capacity diagram of the battery for 50 times of charge and discharge. The first reversible specific capacity of the battery is 1791mAh/g, and the reversible specific capacity after 50 cycles is 1690mAh/g.

Example 2

Take 1g of silica balls with a diameter of about 100nm as the raw material, mix them evenly with 0.5g of metal magnesium powder, place them in a closed environment filled with argon and hydrogen, and raise the temperature to 650°C at a rate of 2°C/min to react for 2h . After the reaction, the product was taken out and dissolved in 0.5 mol/L sulfuric acid to react for 4 hours. After filtering and drying, the intermediate product Si@SiO ₂ and sucrose obtained above were dissolved in the aqueous solution solvent at a mass ratio of 1:10, stirred at 100°C until the water evaporated completely, and the mixture was finely ground and then heated in a nitrogen atmosphere with 10 The heating rate of °C/min was raised to 700 °C for 4 hours. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in hydrofluoric acid with a mass fraction of 2% to react for 2 hours, filtered, washed and dried to obtain the reaction product C@Si. The diameter of the porous nano-silicon core of the obtained product is about 100nm, and the thickness of the carbon layer is about 50nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The first reversible specific capacity of the battery is 982mAh/g, and the reversible specific capacity after 50 cycles is 924mAh/g.

Example 3

Take 1g of silica particles with a diameter of about 500nm as a raw material, mix it with 0.7g of metal magnesium powder, place it in a closed environment filled with argon, and raise the temperature to 700°C at a heating rate of 10°C/min for 4 hours. After the reaction, the product was taken out and dissolved in 2mol/L hydrochloric acid for 8 hours. After filtering and drying, the intermediate product Si@SiO ₂ and polyvinyl alcohol obtained above were dissolved in n-butanol solvent at a mass ratio of 1:15, stirred at 90°C until the ethanol was completely volatilized, and the mixture was finely ground and then heated under argon gas. Under a mixed atmosphere with nitrogen, the temperature was raised to 900° C. at a heating rate of 20° C./min for 6 hours. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in hydrofluoric acid with a mass fraction of 10% and reacted for 0.5 h, filtered, washed and dried to obtain the reaction product C@Si. The diameter of the porous nano-silicon core of the obtained product is about 500nm, and the thickness of the carbon layer is about 20nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The first reversible specific capacity of the battery is 853mAh/g, and the reversible specific capacity after 50 cycles is 798mAh/g.

Example 4

Take 1 g of silica balls with a diameter of about 1 μm as raw materials, mix them with 0.8 g of metal magnesium powder, place them in a closed environment filled with argon, and raise the temperature to 750 °C at a heating rate of 4 °C/min for 6 hours. After the reaction, the product was taken out and dissolved in 3mol/L hydrochloric acid for 4 hours. After filtering and drying, the intermediate product Si@SiO ₂ and epoxy resin obtained above were dissolved in acetone solvent at a mass ratio of 2:1, stirred at 80°C until the acetone was completely volatilized, and the mixture was ground finely and then heated in argon and hydrogen Under the atmosphere, the temperature was raised to 1000° C. for 5 h at a heating rate of 10° C./min. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in hydrofluoric acid with a mass fraction of 10% to react for 1 h, filtered, washed and dried to obtain the reaction product C@Si. The diameter of the porous nano-silicon core of the obtained product is about 1 μm, and the thickness of the carbon layer is about 10 nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The first reversible specific capacity of the battery is 1956mAh/g, and the reversible specific capacity after 50 cycles is 1802mAh/g.

Example 5

Take 1g of silicon dioxide particles with a diameter of about 2 μm as the raw material, mix them with 0.9g of metal magnesium powder, place them in a closed environment filled with hydrogen, and raise the temperature to 700°C at a heating rate of 5°C/min for 8 hours. After the reaction, the product was taken out and dissolved in 1 mol/L sulfuric acid to react for 10 h. After filtering and drying, the intermediate product Si@SiO ₂ and polypropylene obtained above were dissolved in methanol solvent at a mass ratio of 1:2, stirred at 60°C until the methanol was completely volatilized, and the mixture was finely ground and placed in an argon atmosphere. The temperature was raised to 600°C at a heating rate of 20°C/min for 8 hours. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in 5% hydrofluoric acid and reacted for 2 hours, filtered, washed and dried to obtain the reaction product C@Si. The diameter of the porous nano-silicon core of the obtained product is about 2 μm, and the thickness of the carbon layer is about 20 nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The first reversible specific capacity of the battery is 898mAh/g, and the reversible specific capacity after 50 cycles is 814mAh/g.

Example 6

Take 1g of silicon dioxide particles with a diameter of about 8 μm as raw materials, mix them with 1g of metal magnesium powder evenly, place them in a closed environment filled with argon, and raise the temperature to 650°C at a heating rate of 10°C/min for 10 hours. After the reaction, the product was taken out and dissolved in 2mol/L hydrochloric acid for 8 hours. After filtering and drying, the intermediate product Si@SiO ₂ and glucose obtained above were dissolved in a water solvent at a mass ratio of 1:1, stirred at 110°C until the water evaporated completely, and the mixture was ground finely and then heated in a nitrogen atmosphere at 15 The heating rate of °C/min was raised to 800 °C for 6 hours. After the reaction, the obtained product C@Si@SiO ₂ was dissolved in hydrofluoric acid with a mass fraction of 20% to react for 1 h, filtered, washed and dried to obtain the reaction product C@Si. The diameter of the porous nano-silicon core of the obtained product is about 8 μm, and the thickness of the carbon layer is about 5 nm.

The prepared material was made into a negative electrode sheet of a lithium ion battery according to the method of Comparative Example 1, and a test battery was assembled. The first reversible specific capacity of the battery is 1690mAh/g, and the reversible specific capacity after 50 cycles is 1548mAh/g.

Claims (10)

1. a nucleocapsid structure Si-C composite material, it is characterised in that: there is nucleocapsid structure；Described nucleocapsid structure includes by carbon Shell that layer is constituted and the kernel that is made up of porous nano silicon；Between described shell and kernel, there is void layer.

Nucleocapsid structure Si-C composite material the most according to claim 1, it is characterised in that: the size of described kernel is 10nm ～10 μm, the thickness of described shell is 1～200nm.

3. the preparation method of the nucleocapsid structure Si-C composite material described in claim 1 or 2, it is characterised in that: include following step Rapid:

1) silica dioxide granule carries out magnesiothermic reduction reaction by magnesium powder, obtains Si@SiO₂Intermediate；

2) described Si@SiO₂After intermediate carries out in-stiu coating by organic polymer carbon source, carbonization, obtain C@Si@SiO₂Middle Body；

3) described C@Si@SiO₂Intermediate uses Fluohydric acid. corrosion, to obtain final product.

The preparation method of nucleocapsid structure Si-C composite material the most according to claim 3, it is characterised in that: 1) in, dioxy After silicon carbide particle is mixed homogeneously with magnesium powder, it is placed in the closed environment of full protective atmosphere, with the intensification speed of 1～20 DEG C/min Rate is warming up to 600～800 DEG C, carries out reduction reaction 1～12h, obtains Si@SiO₂Intermediate.

The preparation method of nucleocapsid structure Si-C composite material the most according to claim 4, it is characterised in that: described dioxy Silicon carbide particle is 1:0.4～1:1 with the mass ratio of magnesium powder.

6. according to the preparation method of the nucleocapsid structure Si-C composite material described in claim 4 or 5, it is characterised in that: described Silica dioxide granule particle diameter is 10nm～10 μm.

The preparation method of nucleocapsid structure Si-C composite material the most according to claim 3, it is characterised in that: 2) in, described Si@SiO₂Intermediate and organic polymer carbon source are dissolved in solvent, and after mix homogeneously, stirring is evaporated, and gained solid mixture is through grinding After mill, be placed under protective atmosphere, be warming up to 600～1200 DEG C with the heating rate of 1～20 DEG C/min, carry out carbonization 1～ 12h, obtains C@Si@SiO₂Intermediate.

The preparation method of nucleocapsid structure Si-C composite material the most according to claim 7, it is characterised in that: described is organic Macromolecule carbon source and Si SiO₂The mass ratio of intermediate is 100:1～1:100.

9. according to the preparation method of the nucleocapsid structure Si-C composite material described in claim 7 or 8, it is characterised in that: described Organic polymer carbon source is in polyvinyl alcohol, polypropylene, Colophonium, phenolic resin, epoxy resin, glucose, sugarcane sugar and starch At least one.

The preparation method of nucleocapsid structure Si-C composite material the most according to claim 3, it is characterised in that: 3) in, described C@Si@SiO₂Intermediate use mass percent concentration be 1～40% Fluohydric acid. carry out impregnation process 0.01～6h.