High-performance composite silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a high-performance composite silicon-carbon negative electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery negative electrode materials. The composite silicon-carbon negative electrode material with excellent electrochemical performance is synthesized through structural design. The preparation method comprises the following steps: firstly, treating a raw material micron silicon to prepare porous silicon; then compounding the porous silicon with graphite and porous carbon; finally, the composite material is subjected to segmented coating, hard carbon coating is conducted on the first segment, and CVD gas phase coating is conducted on the second segment; the finally obtained composite silicon-carbon negative electrode material improves the first coulombic efficiency and the cycle performance on the basis of obviously improving the specific capacity of the negative electrode of the lithium ion battery.

Description

Technical Field

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

[0002] Lithium-ion batteries are efficient and convenient energy storage devices. However, the graphite anodes commonly used in commercial lithium-ion batteries have a relatively low specific capacity, making it difficult to be used as the anode material for high-energy-density lithium-ion batteries. Among many known new anode materials, silicon has a high theoretical capacity, a low working voltage platform, and is also characterized by rich resource reserves and environmental friendliness, and is regarded as a very promising anode material.

[0003] At room temperature, the product after complete lithiation of silicon material is Li 15 Si4, and the corresponding theoretical capacity is 3579 mAh / g, about 10 times that of commercial graphite anodes (372 mAh / g). However, different from the lithiation mechanism of carbon materials, silicon anodes need to undergo multiple crystallographic phase transitions during the (de)lithiation process, and their volume changes greatly (the volume expansion rate is about 300%), resulting in cracking and pulverization during cycling, which in turn leads to capacity decay, shortened cycle life, and accelerated battery failure of silicon-based lithium-ion batteries.

[0004] From the above characteristics of the silicon anode material, it can be seen that silicon can form Li 15 Si4 alloy with high lithium storage capacity even at room temperature, but at the same time, there are also problems such as serious volume change, which can be summarized as four aspects: pulverization, poor electrical contact, instability of the solid electrolyte interface film, and poor conductivity of the silicon material itself during long-term cycling.

[0005] Therefore, the development of low-cost and high-performance silicon-based anode materials is of great significance for the practical application of high-energy-density lithium-ion batteries. Summary of the Invention

[0006] Aiming at the content mentioned in the background art, the purpose of the present invention is to provide a high-performance composite silicon-carbon anode material and a preparation method thereof. By designing a silicon-carbon anode material with a composite protection structure and a conductive network, the specific capacity of the anode of the lithium-ion battery is significantly improved, and at the same time, the first Coulomb efficiency and cycle performance are improved.

[0007] To achieve the above purpose, the present invention specifically adopts the following technical solutions: The present invention provides a preparation method of a high-performance composite silicon-carbon anode material, including the following steps: Step 1: Mix silicon powder and magnesium powder, and then heat it up to obtain Mg2Si powder; Step 2: Add a dispersion medium to the obtained Mg2Si powder and perform sanding to obtain nano-sized Mg2Si powder, and then remove Mg under high-temperature conditions to obtain porous silicon; Step 3: Disperse the porous silicon with a surfactant, then add graphite and mix with porous carbon, and dry the obtained slurry to obtain powder 1; Step 4: Mix powder 1 with a resin-based carbon source, put it into a furnace for primary coating to obtain primary-coated powder 2; Step 5: Take the primary-coated powder 2 for preheating treatment, then introduce a carbon source gas for CVD gas-phase coating to obtain a G / Si / HC@C powder material, and sieve to obtain the composite silicon-carbon anode material.

[0008] Further, the silicon powder in Step 1 is micron-sized, D 50 is 20 - 30 μm; the mass ratio of the silicon powder to the magnesium powder in the mixture is 1:(1.5 - 5).

[0009] Further, the conditions for heating with temperature increase in Step 1 are: argon atmosphere, oxygen content not exceeding 100 ppm, temperature 500 - 700 °C, rotation speed 2 - 10 rpm, and constant temperature for 2 - 6 h.

[0010] Further, the dispersion medium in Step 2 is n-hexane; the high-temperature conditions are: atmosphere is a N2 / NH3 mixed gas, temperature is 700 - 850 °C, and reaction time is 2 - 6 h.

[0011] Further, the surfactant in Step 3 is tetrabutylammonium fluoride solution.

[0012] Further, the mass ratio of the porous silicon, graphite, and porous carbon in Step 3 is (5 - 15):(75 - 85):(5 - 15).

[0013] Further, the resin-based carbon source in Step 4 is polyvinylpyrrolidone, and its addition amount is 10% - 20% of the mass of powder 1.

[0014] Further, the conditions for the primary coating in Step 4 are: coating temperature is 600 - 900 °C, heating rate is 2 - 10 °C / min, and coating time is 2 - 5 h.

[0015] Further, the conditions for the preheating treatment in Step 5 are: evacuate and then introduce argon, heat up to 450 - 500 °C at a rate of 4 - 6 °C / min and keep warm for 0.5 - 2 h; the conditions for the CVD gas-phase coating are: continue to heat up to 780 - 820 °C at a rate of 4 - 6 °C / min after preheating, then introduce the carbon source gas at a rate of 0.5 - 5 L / min and coat for 4 - 12 h; the carbon source gas is acetylene or methane.

[0016] The present invention also provides a composite silicon-carbon anode material prepared by the above method.

[0017] The present invention synthesizes a composite silicon-carbon anode material with excellent electrochemical performance through structural design: First, the raw material micron silicon is processed to prepare porous silicon (due to the existence of pore structures in porous nano-silicon, its expansion and mass transfer performance are significantly improved compared with the raw material); Subsequently, the porous silicon is compounded with graphite and porous carbon (utilizing the excellent conductivity of graphite and the inhibition of volume expansion by porous carbon to improve the material performance); Finally, the composite material is coated in segments. In the first segment, hard carbon coating is carried out first. The carbon layer of hard carbon has high strength and can effectively inhibit expansion. Secondly, during the pyrolysis process of the hard carbon carbon source, some functional groups and carbon will be generated, which can strengthen the interfacial stability between silicon and graphite and porous carbon; The second-stage coating is CVD gas-phase coating. The gas-phase coating can form a uniform carbon layer, while isolating silicon from contact with some functional groups and electrolytes, and improving the first-cycle efficiency of the material.

[0018] The beneficial effects of the present invention are as follows: 1. Aiming at the most significant "volume expansion" problem of silicon materials, the present invention inhibits it through porous silicon-porous carbon-hard carbon coating; Porous silicon and porous carbon themselves have the effect of inhibiting expansion. At the same time, porous carbon can carry more silicon, improving the capacity of the material. Secondly, the porous structure can shorten the ion transport path, reduce the polarization of the material, and improve the material performance.

[0019] 2. The present invention uses hard carbon to coat and fix silicon once to increase the interfacial stability between silicon and graphite and porous carbon; The secondary CVD gas-phase coating can improve the first-cycle efficiency. Through experimental verification, directly using CVD gas-phase coating cannot effectively inhibit the expansion of silicon, and the coated carbon layer will be damaged. Therefore, the present invention first uses a hard carbon coating layer with high carbon layer hardness and strength to inhibit volume expansion. For the problem of low first-cycle efficiency of the hard carbon coating layer, then use the CVD coating layer for "surface smoothing" modification, improving the first-cycle efficiency while strengthening the strength of the carbon layer and better inhibiting volume expansion. Description of the Drawings

[0020] Figure 1 It is the SEM image of the material prepared in Example 1 of the present invention.

[0021] Figure 2 It is the TEM image of the material prepared in Example 1 of the present invention.

[0022] Figure 3 It is the 1C full charge-discharge cycle curve of the material prepared in Example 1 of the present invention. Detailed Embodiments

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with embodiments. Those not specifying specific conditions in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not indicating the manufacturer can all be obtained as conventional products through commercial purchase.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0025] Example 1 A preparation method of a high-performance composite silicon-carbon anode material, comprising: Step 1: First, micron-sized silicon powder (D 50 = 20 - 30 μm) and magnesium powder are put into a ribbon mixer according to a mass ratio of 1:1.75. After mixing for 45 min, they are put into the transfer bin of an atmosphere rotary furnace. Ar is introduced for gas replacement to reduce the oxygen content inside the bin to below 100 ppm. The rotary atmosphere furnace is heated to 520 °C, with a rotation speed of 2 rpm. After maintaining the temperature for 4 h, the material is discharged to obtain Mg2Si powder.

[0026] Step 2: The Mg2Si powder obtained in Step 1 is dispersed in n-hexane for sanding and classification to obtain nano-sized Mg2Si powder. The nano-sized Mg2Si powder is put into an atmosphere furnace. The temperature in the reaction zone inside the furnace is 820 °C, the atmosphere is a N2 / NH3 mixed gas, and the reaction time is 3 h. After discharging, pickling, water washing, and drying are carried out to obtain the finished porous silicon.

[0027] Step 3: The porous silicon obtained in Step 2 is added to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the porous silicon. Subsequently, graphite and porous carbon are added for dispersion and mixing (the mass ratio of porous silicon, graphite, and porous carbon in the mixture is 8:80:12) to obtain a mixed slurry. The mixed slurry is dried to obtain powder 1.

[0028] Step 4: 15% of polyvinylpyrrolidone by mass of the powder 1 obtained in Step 3 is added for mixing. After mixing, it is put into an atmosphere furnace for primary coating. The coating temperature is 800 °C, the coating time is 4 h, and the heating rate is 5 °C / min. After cooling, the material is discharged to obtain the primary-coated powder 2.

[0029] Step 5: Take the primary coated powder 2 obtained in Step 4 and place it in a reaction kettle. Vacuum the inside of the reaction kettle, then introduce Ar2 (2 L / min), heat it up to 480 °C at a rate of 5 °C / min, and keep it at this temperature for 30 min. Then continue to heat it up to 800 °C at a rate of 5 °C / min, and introduce acetylene gas for CVD gas-phase coating. The flow rate of the introduced acetylene gas is 0.5 L / min, and the coating time is 4 h to obtain the G / Si / HC@C powder material.

[0030] Step 6: Screen and classify the G / Si / HC@C powder material obtained in Step 5 with a 325-mesh molecular sieve to obtain the finished composite silicon-carbon anode material.

[0031] Example 2 A preparation method of a high-performance composite silicon-carbon anode material, comprising: Step 1: First, put micron silicon powder (D 50 = 20 - 30 μm) and magnesium powder into a ribbon mixer according to a mass ratio of 1:2. After mixing for 45 min, put them into the transfer bin of an atmosphere rotary furnace, introduce Ar for gas replacement, reduce the oxygen content inside the bin to below 100 ppm, heat the rotary atmosphere furnace to 520 °C, with a rotation speed of 2 rpm, and discharge the material after keeping it at a constant temperature for 4 h to obtain Mg2Si powder.

[0032] Step 2: Disperse the Mg2Si powder obtained in Step 1 in n-hexane for sanding and classification to obtain nano-Mg2Si powder. Put the nano-Mg2Si powder into an atmosphere furnace, with the temperature in the reaction zone of the furnace being 820 °C, the atmosphere being a N2 / NH3 mixed gas, and the reaction time being 3 h. After discharging, carry out pickling, water washing, and drying to obtain the finished porous silicon.

[0033] Step 3: Add the porous silicon obtained in Step 2 to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the porous silicon. Then add graphite and porous carbon for dispersion and mixing (the mass ratio of porous silicon, graphite, and porous carbon is 8:80:12) to obtain a mixed slurry. Dry the mixed slurry to obtain powder 1.

[0034] Step 4: Add 15% of its mass of polyvinylpyrrolidone to the powder 1 obtained in Step 3 for mixing. After mixing, put it into an atmosphere furnace for primary coating. The coating temperature is 800 °C, the coating time is 4 h, and the heating rate is 5 °C / min. After cooling, discharge the material to obtain the primary coated powder 2.

[0035] Step 5: Take the primary coated powder 2 obtained in Step 4 and place it in a reaction kettle. Vacuum the inside of the reaction kettle, then introduce Ar2 (2 L / min), heat it to 480 °C at a rate of 5 °C / min, and hold the temperature for 30 min; then continue to heat it to 800 °C at a rate of 5 °C / min, and introduce acetylene gas for CVD gas phase coating. The flow rate of the introduced acetylene gas is 0.5 L / min, and the coating time is 4 h to obtain the G / Si / HC@C powder material.

[0036] Step 6: Screen and classify the G / Si / HC@C powder material obtained in Step 5 with a 325-mesh molecular sieve to obtain the finished composite silicon-carbon anode material.

[0037] Example 3 A preparation method of a high-performance composite silicon-carbon anode material, comprising: Step 1: First, put micron silicon powder (D 50 = 20 - 30 μm) and magnesium powder into a ribbon mixer according to a mass ratio of 1:1.75. After mixing for 45 min, put them into the transfer bin of an atmosphere rotary furnace, introduce Ar for gas replacement, reduce the oxygen content inside the bin to below 100 ppm, heat the rotary atmosphere furnace to 520 °C, rotate at a speed of 2 rpm, keep the temperature constant for 4 h, and then discharge to obtain Mg2Si powder.

[0038] Step 2: Disperse the Mg2Si powder obtained in Step 1 in n-hexane for sanding and classification to obtain nano-Mg2Si powder. Put the nano-Mg2Si powder into an atmosphere furnace, the temperature of the reaction zone inside the furnace is 820 °C, the atmosphere is a N2 / NH3 mixed gas, and the reaction time is 3 h; after discharging, perform pickling, water washing, and drying to obtain the finished porous silicon.

[0039] Step 3: Add the porous silicon obtained in Step 2 to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the porous silicon. Then add graphite and porous carbon for dispersion and mixing (the mass ratio of porous silicon, graphite, and porous carbon is 12:80:8) to obtain a mixed slurry, and dry the mixed slurry to obtain powder 1.

[0040] Step 4: Add 15% of its mass of polyvinylpyrrolidone to the powder 1 obtained in Step 3 for mixing. After mixing, put it into an atmosphere furnace for primary coating. The coating temperature is 800 °C, the coating time is 4 h, and the heating rate is 5 °C / min; after cooling, discharge to obtain the primary coated powder 2.

[0041] Step 5: Take the primary coated powder 2 obtained in Step 4 and place it in a reaction kettle. Vacuum the inside of the reaction kettle, then introduce Ar₂ (2 L / min), heat it up to 480 °C at a rate of 5 °C / min, and keep it at this temperature for 30 min; then continue to heat it up to 800 °C at a rate of 5 °C / min, and introduce acetylene gas for CVD gas-phase coating. The flow rate of the introduced acetylene gas is 0.5 L / min, and the coating time is 4 h to obtain the G / Si / HC@C powder material.

[0042] Step 6: Screen and classify the G / Si / HC@C powder material obtained in Step 5 with a 325-mesh molecular sieve to obtain the finished composite silicon-carbon anode material.

[0043] Comparative Example 1 Step 1: First, put micron silicon powder (D 50 = 20 - 30 μm) and magnesium powder into a ribbon mixer at a mass ratio of 1:1.75. After mixing for 45 min, put them into the transfer bin of an atmosphere rotary furnace, introduce Ar for gas replacement, reduce the oxygen content inside the bin to below 100 ppm, heat the atmosphere rotary furnace to 520 °C, with a rotation speed of 2 rpm, and discharge the material after keeping it at a constant temperature for 4 h to obtain Mg₂Si powder.

[0044] Step 2: Disperse the Mg₂Si powder obtained in Step 1 in n-hexane for sanding and classification to obtain nano-Mg₂Si powder. Put the nano-Mg₂Si powder into an atmosphere furnace, the temperature of the reaction zone inside the furnace is 820 °C, the atmosphere is a N₂ / NH₃ mixed gas, and the reaction time is 3 h; after discharging, carry out pickling, washing with water, and drying to obtain the finished porous silicon.

[0045] Step 3: Add the porous silicon obtained in Step 2 to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the porous silicon. Then add graphite and porous carbon for dispersion and mixing (the mass ratio of porous silicon, graphite, and porous carbon is 8:80:12) to obtain a mixed slurry. Dry the mixed slurry to obtain powder 1.

[0046] Step 4: Take the powder 1 obtained in Step 3 and place it in a reaction kettle. Vacuum the inside of the reaction kettle, then introduce Ar₂ (2 L / min), heat it up to 480 °C at a rate of 5 °C / min, and keep it at this temperature for 30 min; then continue to heat it up to 800 °C at a rate of 5 °C / min, and introduce acetylene gas for CVD gas-phase coating. The flow rate of the introduced acetylene gas is 0.5 L / min, and the coating time is 4 h to obtain the G / Si / C@C powder material.

[0047] Step 5: Screen and classify the G / Si / C@C powder material obtained in Step 4 with a 325-mesh molecular sieve to obtain the finished composite silicon-carbon anode material.

[0048] Comparative Example 2 Step 1: First, put micron silicon powder (D 50 = 20 - 30 μm) and magnesium powder into a ribbon mixer according to a mass ratio of 1:1.75. After mixing for 45 min, put them into the transfer bin of an atmosphere rotary furnace, introduce Ar for gas replacement, reduce the oxygen content inside the bin to below 100 ppm, heat the rotary atmosphere furnace to 520 °C, with a rotation speed of 2 rpm, keep the temperature constant for 4 h, and then discharge to obtain Mg2Si powder.

[0049] Step 2: Disperse the Mg2Si powder obtained in Step 1 in n - hexane for sanding, and classify to obtain nano - Mg2Si powder. Put the nano - Mg2Si powder into an atmosphere furnace, with the temperature in the reaction zone inside the furnace being 820 °C, the atmosphere being a N2 / NH3 mixed gas, and the reaction time being 3 h; after discharging, carry out pickling, water washing, and drying to obtain the finished porous silicon.

[0050] Step 3: Add the porous silicon obtained in Step 2 to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the porous silicon. Subsequently, add graphite and porous carbon for dispersion and mixing (the mass ratio of porous silicon, graphite, and porous carbon is 8:80:12) to obtain a mixed slurry, and dry the mixed slurry to obtain powder 1.

[0051] Step 4: Add 15% of its mass of polyvinylpyrrolidone to the powder 1 obtained in Step 3 for mixing. After mixing, put it into an atmosphere furnace for primary coating, with the coating temperature being 800 °C, the coating time being 4 h, and the heating rate being 5 °C / min; after cooling, discharge to obtain the primary - coated powder 2.

[0052] Step 5: Screen and classify the primary - coated powder 2 obtained in Step 4 with a 325 - mesh molecular sieve to obtain the silicon - carbon anode material.

[0053] Comparative Example 3 Step 1: First, put micron silicon powder (D 50 = 20 - 30 μm) into a ball - milling tank, and then add polyvinyl alcohol and zirconia beads with a diameter of 0.3 mm (ball - to - material ratio of 5:1, polyvinyl alcohol content of 8%); alternately ball - mill at a speed of 800 rpm for 16 h, and then carry out filtration and washing to obtain a nano - silicon solution.

[0054] Step 2: Add the nano - silicon solution obtained in Step 1 to a tetrabutylammonium fluoride solution for stirring and dispersion to prevent the aggregation of the nano - silicon. Subsequently, add graphite and porous carbon for dispersion and mixing (the mass ratio of nano - silicon, graphite, and porous carbon is 8:80:12) to obtain a mixed slurry, and dry the mixed slurry to obtain powder 1.

[0055] Step 3: Add polyvinylpyrrolidone accounting for 15% of the mass of the powder 1 obtained in Step 2 and mix them. After mixing, put them into an atmosphere furnace for primary coating. The coating temperature is 800 °C, the coating time is 4 h, and the heating rate is 5 °C / min. After cooling, discharge to obtain the primary coated powder 2.

[0056] Step 4: Take the primary coated powder 2 obtained in Step 3 and place it in a reaction kettle. Vacuumize the inside of the reaction kettle, and then introduce Ar2 (2 L / min), heat it to 480 °C at a rate of 5 °C / min, and keep it warm for 30 min. Then continue to heat it to 800 °C at a rate of 5 °C / min, and introduce acetylene gas for CVD gas phase coating. The flow rate of the introduced acetylene gas is 0.5 L / min, and the coating time is 4 h to obtain the G / Si / C@C powder material.

[0057] Step 5: Screen and classify the G / Si / C@C powder material obtained in Step 4 with a 325-mesh molecular sieve to obtain the finished composite silicon-carbon anode material.

[0058] To detect the performance of the composite silicon-carbon anode material of the present invention, a half-cell test method, 18650 steel shell full cell, scanning electron microscope, and specific surface area and porosity analyzer are used for testing.

[0059] 1) The half-cell test method is to use the silicon-carbon anode materials prepared in the examples and comparative examples as the negative electrode active materials to prepare a slurry. The slurry ratio is active material: CNTs (including dispersant): CMC: SBR = 89%: 4.5%: 1.5%: 5%. Then coat the slurry on the copper foil and vacuum dry it for 12 h to make a negative electrode sheet. The electrolyte is commercially purchased, the separator is a PE membrane, and the lithium sheet is the counter electrode. Assemble it into a half-cell in a glove box. Conduct a constant current charge-discharge experiment on a LAND battery test system. The charge-discharge voltage is limited to 0.005 - 2 V. Unless otherwise specified, the following data are all charged and discharged at 1 C, and a computer-controlled charge-discharge cabinet is used for data acquisition and control.

[0060] 2) Table 1 shows the test results of the coin cell performance of the examples and comparative examples: Table 1 Test Results of Coin Cell Performance

[0061] As can be seen from Table 1, considering the first efficiency and cycle stability comprehensively, Example 1 has the best electrochemical performance; Example 3 has the highest capacity, which is due to the highest silicon content ratio (12%), but the cycle stability is significantly lower than that of Example 1 and Example 2, which is caused by the increase in the silicon content ratio and the decrease in the porous carbon ratio; Comparative Example 1 lacks the first layer of hard carbon protection layer, and the result shows that its cycle stability is the worst; Comparative Example 2 has no CVD coating layer, and its first efficiency is significantly lower than that of other cases; Comparative Example 3 uses nano-silicon, and its cycle stability is not as good as that of porous silicon.

[0062] Figure 1 SEM image of the material prepared in Example 1 of the present invention; From Figure 1 the view, all the nano-silicon is covered by a carbon coating layer, and there is no free or agglomerated nano-silicon. Figure 2 TEM image of the material prepared in Example 1 of the present invention; Figure 2 It further proves the existence of an amorphous coating layer in the material. Since the outermost layer is coated by CVD chemical vapor deposition, the coating layer has good uniformity.

[0063] Figure 3 1C full charge-discharge cycle curve of the material prepared in Example 1 of the present invention; Figure 3 It is the full cell test of Example 1. A soft-pack battery was assembled with lithium cobaltate as the positive electrode and silicon-carbon composite material (compound capacity 500 mAh / g) as the negative electrode for 1C cycle test. The test results show that the capacity retention rate is about 96% at 200 cycles, and it has good cycle performance.

[0064] The embodiments described above only represent several preferred embodiments of the present invention. The description is relatively specific and detailed, but it does not limit the present invention. It should be pointed out that for those skilled in the art, the present invention can also have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the concept and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high-performance composite silicon-carbon anode material, characterized in that, It includes the following steps: Step 1: Mix silicon powder and magnesium powder, and then heat it up to obtain Mg2Si powder; Step 2: Add a dispersion medium to the obtained Mg2Si powder for sanding to obtain nano-Mg2Si powder, and then remove Mg under high-temperature conditions to obtain porous silicon; Step 3: Disperse the porous silicon with a surfactant, then add graphite and porous carbon for mixing, and dry the obtained slurry to obtain powder 1; Step 4: Mix powder 1 with a resin-based carbon source, put it into a furnace for primary coating to obtain primary-coated powder 2; Step 5: Take the primary-coated powder 2 for preheating treatment, and then introduce a carbon source gas for CVD gas-phase coating to obtain G / Si / HC@C powder material, and sieve to obtain the composite silicon-carbon anode material.

2. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, wherein The silicon powder described in Step 1 is micron-sized, and D 50 is 20 - 30 μm; the mass ratio of the silicon powder to the magnesium powder in the mixture is 1:(1.5 - 5).

3. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, wherein The conditions for the heating-up in Step 1 are: argon atmosphere, oxygen content not exceeding 100 ppm, temperature of 500 - 700 °C, rotation speed of 2 - 10 rpm, and constant temperature for 2 - 6 h.

4. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, characterized in that, The dispersion medium in Step 2 is n-hexane; the high-temperature conditions are: atmosphere is N2 / NH3 mixed gas, temperature is 700 - 850 °C, and reaction time is 2 - 6 h.

5. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, characterized in that The surfactant in Step 3 is tetrabutylammonium fluoride solution.

6. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, wherein The mass ratio of the mixture of porous silicon, graphite and porous carbon in Step 3 is (5 - 15):(75 - 85):(5 - 15).

7. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, wherein, The resin-based carbon source in Step 4 is polyvinylpyrrolidone, and its addition amount is 10% - 20% of the mass of powder 1.

8. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, characterized in that The conditions for the primary coating in Step 4 are: coating temperature is 600 - 900 °C, heating rate is 2 - 10 °C / min, and coating time is 2 - 5 h.

9. The preparation method of the high-performance composite silicon-carbon anode material according to claim 1, characterized in that The conditions for the preheating treatment in Step 5 are: evacuate and then introduce argon, heat up to 450 - 500 °C at a rate of 4 - 6 °C / min and hold for 0.5 - 2 h; the conditions for the CVD gas-phase coating are: continue to heat up to 780 - 820 °C at a rate of 4 - 6 °C / min after preheating, and then introduce the carbon source gas at a rate of 0.5 - 5 L / min for coating for 4 - 12 h; the carbon source gas is acetylene or methane.

10. The composite silicon-carbon anode material prepared by the method according to any one of claims 1 - 9.

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