Hyperbranched polyimide-derived silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention provides a preparation method of a hyperbranched polyimide-derived silicon-carbon negative electrode material, which comprises the following steps: S1, preparation of a carbon precursor: mixing 1, 3, 5-tris (4-aminophenyl) benzene and 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride for reaction to prepare hyperbranched polyimide; s2, preparing porous carbon; and S3, vapor phase silicon carbon deposition. The invention also correspondingly provides a silicon-carbon negative electrode, a lithium ion battery and an electrochemical device. According to the hyperbranched polyimide-derived silicon-carbon negative electrode material, the volume expansion of silicon in the lithium intercalation process is effectively relieved, the active material is prevented from falling off, and the cycling stability of the battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and particularly relates to a hyperbranched polyimide-derived silicon-carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] With the development of the new energy industry, the actual specific capacity of the graphite negative electrode has approached its theoretical value (372 mAh / g), but still cannot well meet the demand of people for energy density. The theoretical specific capacity of silicon is about 3579 mAh / g, which is much higher than 372 mAh / g of the graphite, and therefore has very high energy density potential. Therefore, the silicon-carbon electrode (Si-C electrode) has become an important development direction of the negative electrode material of the ion battery.

[0003] However, in actual application, the silicon will have a huge volume expansion in the process of lithium ion insertion and extraction. Due to the expansion and contraction of the silicon, the structure of the electrode material will change, leading to poor contact, and further affecting the cycle stability and capacity retention rate of the battery. SUMMARY

[0004] In order to solve the problems in the prior art, the application provides a silicon-carbon negative electrode material and a preparation method thereof, which effectively alleviates the volume expansion (up to 300%) of the silicon in the lithium insertion process, prevents the active material from falling off, and improves the cycle stability of the battery.

[0005] A first object of the application is to provide a preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0006] S1, preparation of a carbon precursor:

[0007] In an inert gas environment, 1,3,5-tris(4-aminophenyl)benzene is dissolved in a solvent under ice water bath conditions, and is mixed with 4,4'-(hexafluoroisopropylidene) diphthalic anhydride under ice water bath conditions to carry out a reaction, to obtain a hyperbranched polyamide acid solution, which is placed in water to precipitate a polymer and dried to obtain polymer particles; the polymer particles are placed in a mixed solution of excess acetic anhydride and pyridine to carry out chemical imidization, to obtain a powder, and then the powder is heat-treated to obtain a hyperbranched polyimide;

[0008] S2, preparation of a porous carbon:

[0009] The carbon precursor obtained in step S1 is placed in a tube furnace, heated to 600-1000℃ at 2-15℃ / min under N2 atmosphere, kept for 2h, and then naturally cooled to room temperature under N2 atmosphere, to obtain a porous carbon material;

[0010] S3, gas-phase silicon-carbon deposition;

[0011] As preferred, the gas-phase silicon-carbon deposition is specifically: under N2 condition, temperature is raised to 350-600℃, then 20% SiH4-N2 mixed gas is introduced, and the temperature is kept at 350-600℃ for 12-20h; then 10% C2H2-N2 mixed gas is introduced, and the temperature is kept at 350-600℃ for 2-4h; finally, natural cooling is performed under N2 atmosphere, to obtain the silicon-carbon negative electrode material.

[0012] The principle of the present application is as follows:

[0013] Firstly, the porous carbon material formed after carbonization of the carbon precursor (Hyperbranched Polyimide, HBPI) of the present application has unique microporous structure and active site characteristics, mainly embodied in the following aspects:

[0014] 1) Microporous structure characteristics:

[0015] High specific surface area: the carbonized HBPI usually has a significant specific surface area (usually up to several hundred to several thousand m 2 / g), which is due to the formation of abundant micropores and mesopores in the pyrolysis process of the hyperbranched molecular structure, which is beneficial to the rapid diffusion and storage of lithium ions in the electrode material.

[0016] Rich micropore / mesopore ratio: the hyperbranched structure makes it easier for local gas release (such as CO, CO2 and NH3) to occur during carbonization, leaving a large number of micropores (<2nm) and mesopores (2-50nm) in the carbon skeleton. This multi-level pore structure helps the penetration of electrolyte and ion transmission, improving the rate performance and cycle stability.

[0017] Uniform structure: unlike linear polymers, the 1,3,5-tris(4-aminophenyl)benzene structure contains three amino units that can extend the polymer structure chain in three directions. High-temperature heat treatment is performed for crosslinking at 360-400℃, which is beneficial to the crosslinking of polymer chains. The symmetry and geometric structure of the monomer affect the degree of branching of the polymer. Selecting monomers with higher symmetry can control the hyperbranched structure, thereby optimizing the pore size distribution. High temperature may cause crosslinking, increasing the degree of branching, which is beneficial to smaller pore structure, thereby obtaining a more controllable pore size distribution and structural uniformity after carbonization, and improving the structure designability of the material.

[0018] 2) Active site characteristics:

[0019] Rich heteroatom (N, O, etc.) doping sites: hyperbranched polyimide contains a large number of imide groups and aromatic rings, and during carbonization, these nitrogen and oxygen elements will be partially retained in the carbon skeleton to form N-doped structures (such as pyrrole-type N, graphite-type N, nitrogen-oxygen heterocycle, etc.), providing abundant electrochemically active sites, improving reaction activity and electronic conductivity.

[0020] Uniformly distributed defect sites and edge carbon sites: due to the high incompleteness of carbonization of the hyperbranched structure, a large number of structural defects and edge active carbon sites are left on the surface of the carbon material, which can provide more positions for lithium ion adsorption and intercalation, thereby improving the specific capacity.

[0021] Therefore, the hyperbranched polyimide after carbonization is an advanced carbon material with high designability, structural porosity and rich functional sites, which has great application potential in the field of energy storage such as lithium ion batteries and supercapacitors.

[0022] Secondly, after carbonization of the hyperbranched polyimide (HBPI) of the present application, as a structural support and conductive matrix, a silicon-carbon composite material with excellent structure can be prepared by introducing a silicon-containing precursor through chemical vapor deposition (CVD), and applied to the negative electrode of lithium ion batteries (LIBs) has the following advantages:

[0023] 1) Structural synergy advantage

[0024] Three-dimensional porous framework facilitates silicon distribution: the porous structure of HBPI after carbonization provides a large amount of loading space, which can realize uniform deposition or coating of silicon, effectively prevent silicon particle agglomeration, and help to build a stable composite structure.

[0025] Flexible buffer structure absorbs volume change: hard carbon derived from HBPI has a certain flexibility and structural buffering capacity, which can effectively alleviate the volume expansion (up to 300%) of silicon during lithium intercalation, prevent active material from falling off, and improve cycle stability.

[0026] 2) Improved conductivity and interface performance

[0027] Highly conductive carbon skeleton: carbonized HBPI has a continuous conductive network, which significantly improves the electronic conductivity of the silicon-carbon composite material, is conducive to fast charge transfer, and improves the rate performance.

[0028] Rich active sites improve interface reaction: N-doped or structural defect sites in HBPI carbon material not only provide lithium ion storage sites, but also enhance the interface bonding force between carbon and silicon, thereby improving the cycle stability.

[0029] As a preferred, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride is 1:1-1:2;

[0030] As preferred, the molar ratio of the 1,3,5-tris(4-aminophenyl)benzene and the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 1:1.1-1:1.35;

[0031] As most preferred, the molar ratio of the 1,3,5-tris(4-aminophenyl)benzene and the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 1:1.31.

[0032] As preferred, in the step S1, the solvent in the reaction includes at least one of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP).

[0033] As preferred, in the step S1, the molar ratio of the acetic anhydride and the pyridine is 1:1.

[0034] As preferred, in the step S1, the time of the chemical imidization is 10-24h.

[0035] As preferred, in the step S1, the heat treatment is specifically that the obtained powder is heat treated at 360-400℃ for 2-4h.

[0036] A second object of the present application is to provide a silicon-carbon negative electrode material, which is prepared by the above method.

[0037] A third object of the present application is to provide a silicon-carbon negative electrode, which comprises the above silicon-carbon negative electrode material.

[0038] As preferred, 90-91wt% of the above silicon-carbon negative electrode material, 4-5wt% of carbon nanotubes, and 5wt% of a binder are mixed with deionized water, and a homogenizer is used to prepare a paste; the paste is uniformly scraped on a copper foil, and then baked in a drying oven to obtain a silicon-carbon negative electrode.

[0039] A fourth object of the present application is to provide a lithium ion battery, which comprises the above silicon-carbon negative electrode.

[0040] A fifth object of the present application is to provide an electrochemical device, which comprises the above lithium ion battery.

[0041] The silicon-carbon negative electrode material of the present application can effectively alleviate the volume expansion of silicon during the lithium intercalation process, prevent the active material from falling off, and improve the cycle stability of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application and, together with the description, serve to explain the present application, and do not constitute a limitation of the present application. In the drawings:

[0043] Figure 1 Scanning electron microscope image of the carbon precursor obtained for Example 2.

[0044] Figure 2 Scanning electron microscope image of the carbon precursor obtained for Comparative Example 2. DETAILED DESCRIPTION

[0045] The following examples facilitate a better understanding of the present application, but do not limit the present application. In the following examples, the experimental methods are conventional methods unless otherwise specified. In the following examples, the test materials used are commercially available from conventional biochemical reagent companies unless otherwise specified. In the following examples, the quantitative tests are set up with three repeated experiments, and the results are averaged.

[0046] First, the preparation method of the silicon-carbon negative electrode material of the present application is as follows:

[0047] (1) Preparation of carbon precursor (hyperbranched polyimide):

[0048] Dissolve 0.48 mmol of 1,3,5-tris(4-aminophenyl)benzene in 10 mL of dimethylformamide (DMF), and under inert gas protection conditions, fully stir in an ice water bath for 30 min. After the raw material is fully dissolved, weigh 0.48 mmol-0.96 mmol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and add it to the above 1,3,5-tris(4-aminophenyl)benzene solution. Keep it under mechanical stirring for 30 min-2 h, then precipitate the polymer in normal temperature water, and vacuum dry to obtain polymer particles. Place the polymer particles in a large amount of a mixture of acetic anhydride and pyridine for 10-24 h for chemical imidization (molar ratio 1:1), wash with water, collect the precipitate by filtration and dry to obtain hyperbranched polyimide powder. Finally, heat treat the obtained powder at 360-400℃ for 2-4 h to facilitate thermal crosslinking between the polyimide chains, and obtain the carbon precursor (hyperbranched polyimide).

[0049] (2) Preparation of porous carbon

[0050] Place the carbon precursor obtained in step (1) in a tube furnace, heat it to 600-1000℃ at 2-15℃ / min under N2 atmosphere, keep it for 2 h, and then naturally cool it to room temperature under N2 atmosphere, to obtain a porous carbon material.

[0051] (3) Gas phase silicon-carbon deposition

[0052] Under the condition of N2, temperature is raised to 350-600℃, then change to volume percentage 20% SiH4-N2 mixed gas, keep at 350-600℃ for 12-20h; change to volume percentage 10% C2H2-N2 mixed gas, keep at 350-600℃ for 2-4h; finally, keep in N2 atmosphere, and then naturally cool down, to obtain the silicon-carbon negative electrode material.

[0053] The specific surface area of the porous carbon prepared by the method of the application is 750-880m 2 / g, the pore volume is 0.32-0.38cm 3 / g, the average pore size is 0.75-0.96nm, and the resistivity is 40-48mΩ·cm.

[0054] II. Preparation of silicon-carbon negative electrode

[0055] The silicon-carbon negative electrode material prepared in step one is mixed with carbon nanotubes, binder carboxymethyl cellulose sodium CMC / polyacrylic acid LA136D according to the mass ratio of 90-91:4-5:5, and a proper amount of deionized water is added, and a homogenizer is used to prepare a paste. The paste is uniformly scraped on a copper foil with a thickness of 180μm, and then baked in a drying oven to prepare an electrode sheet.

[0056] III. Preparation of lithium ion battery

[0057] According to the method in the prior art, the silicon-carbon negative electrode sheet prepared in step two, a separator, a positive electrode sheet, an electrolyte and the like are prepared into a lithium ion battery.

[0058] The lithium ion battery prepared by using the silicon-carbon negative electrode material of the application has a first delithiation specific capacity of 1323-1602mAh / g, a first coulombic efficiency of 89.9-91.5%, a capacity retention rate of 80.3-84.6%, and a rate performance of the cell of 2C:98.25-99.12%; 3C:95.48-97.13%; 5C:78.25-87.88%.

[0059] IV. Electrochemical device

[0060] When the lithium ion battery of the application is used as a power source, it can be used in large electrochemical devices, such as electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems and the like. When applied to large devices, a battery pack or a battery module can be used. The lithium ion battery of the application can also be applied to small electrochemical devices such as tablet computers, mobile phones, notebook computers and the like.

[0061] Example 1

[0062] I. The preparation method of the silicon-carbon negative electrode material of the application is as follows:

[0063] (1) Preparation of carbon precursor (hyperbranched polyimide particles):

[0064] Dissolve 1,3,5-tris(4-aminophenyl)benzene (0.14 g, 0.48 mmol) in 10 mL of dimethylformamide (DMF) and stir thoroughly under argon protection conditions in an ice water bath for 30 min. After the raw material is fully dissolved, weigh 6FDA 0.28 g, 0.63 mmol) and add to the 1,3,5-tris(4-aminophenyl)benzene solution. Keep stirring for 30 min under mechanical stirring, then obtain a hyperbranched polyamide acid (polyimide precursor) solution. Then place it in normal temperature water to precipitate the polymer, and vacuum dry to obtain polymer particles. Place the polymer particles in a large amount of a mixture of acetic anhydride and pyridine for 15 h for chemical imidization (molar ratio 5:5), wash with water, collect the precipitate by filtration and dry to obtain hyperbranched polyimide powder. Finally, heat treat the obtained powder at 380℃ for 2 h to obtain carbon precursor hyperbranched polyimide particles.

[0065] (2) Preparation of porous carbon

[0066] Place the carbon precursor powder obtained in step (1) in a tube furnace, heat to 750℃ at 5℃ / min under N2 atmosphere, keep for 2 h, and naturally cool to room temperature after N2 atmosphere to obtain a porous carbon material.

[0067] (3) Gas phase silicon-carbon deposition

[0068] Heat to 450℃ under N2 conditions, then change to a volume percentage of 20% SiH4-N2 mixed gas, keep at 450℃ for 12 h; change to a volume percentage of 10% C2H2-N2 mixed gas, keep at 380℃ for 3.5 h; finally, naturally cool down after N2 atmosphere to obtain a silicon-carbon negative electrode material.

[0069] II. Preparation of silicon-carbon negative electrode

[0070] Mix the silicon-carbon negative electrode material prepared in step one with carbon nanotubes and polyacrylic acid LA136D according to a mass ratio of 90:5:5, add an appropriate amount of deionized water, and use a homogenizer to prepare a paste. Uniformly scrape the paste onto a copper foil with a thickness of 180 μm, and then bake in a drying oven to prepare an electrode sheet.

[0071] III. Preparation of lithium ion battery

[0072] Wind the silicon-carbon negative electrode sheet prepared in step two, a separator and a positive electrode sheet to obtain a cell, assemble the cell into a battery shell, dry, inject electrolyte, package, form, and divide to obtain a lithium ion battery.

[0073] Example 2

[0074] The difference between this example and Example 1 is that the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 1:1.1. The rest of the parameters and steps are the same as those of Example 1.

[0075] Figure 1 The scanning electron microscope image of the carbon precursor obtained in Example 2.

[0076] Example 3

[0077] The difference between this example and Example 1 is that the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is 1:2. The rest of the parameters and steps are the same as those of Example 1.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that the raw material 1,3,5-tris(4-aminophenyl)benzene is replaced by an equal molar amount of 1,2-bis(4-aminophenyl)benzene. The rest of the parameters and steps are the same as those of Example 1.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Example 1 is that the raw material 1,3,5-tris(4-aminophenyl)benzene is replaced by an equal molar amount of 4,4'-diamino diphenyl ether. The rest of the parameters and steps are the same as those of Example 1.

[0082] Figure 2 The scanning electron microscope image of the carbon precursor obtained in Comparative Example 2.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 is that the raw material 1,3,5-tris(4-aminophenyl)benzene is replaced by an equal molar amount of 4,4'4"-triaminotriphenylamine. The rest of the parameters and steps are the same as those of Example 1.

[0085] Test Example

[0086] The performance of the silicon-carbon negative electrode material, silicon-carbon negative electrode and lithium ion battery prepared in each of the examples and comparative examples of the present application was tested.

[0087] The specific surface area, pore volume, average pore size and resistivity of the porous carbon obtained in each of the above examples and comparative examples (i.e. prepared according to step (2) of each example) were tested. The test data are shown in Table 1.

[0088] The silicon-carbon negative electrode material obtained in each of the above examples and comparative examples was used to prepare test batteries (CR2025 lithium ion half batteries), and the first lithium extraction specific capacity, first coulombic efficiency, capacity retention rate, rate performance of the battery cell, etc. were tested. The data are shown in Table 2. Among them,

[0089] The preparation method of the CR2025 lithium ion half battery comprises the following steps:

[0090] The silicon-carbon negative electrode material prepared above is mixed with carbon nanotubes and polyacrylic acid LA136D according to a mass ratio of 90:5:5, and a proper amount of deionized water is added to prepare a paste using a homogenizer. The paste is uniformly scraped on a copper foil with a thickness of 180 μm, and then baked in a drying oven to prepare a negative electrode sheet.

[0091] The baked negative electrode sheet is pressed and cut into a circular electrode with a diameter of 16 mm. The circular electrode is sequentially and neatly stacked in a glove box according to the order of a negative electrode shell, a spring sheet, a gasket, a lithium sheet, a separator, the circular electrode, and a positive electrode shell, and electrolyte is injected to obtain a CR2025 lithium ion half battery.

[0092] Performance test method:

[0093] Unless otherwise specified, the initial lithium extraction specific capacity, the initial coulombic efficiency, the capacity retention rate, and the rate performance of the battery core of the present application are obtained by charging and discharging test of the above-mentioned CR2025 lithium ion half battery using a battery test system.

[0094] 1. Initial lithium extraction specific capacity

[0095] The above battery is discharged to 0 V using a 0.05 C current, and then discharged to 0 V using a 50 uA current after 3 min of static state, to obtain the initial lithium intercalation specific capacity of the silicon-carbon material. Then the above battery is discharged using a 0.05 C current until the voltage is greater than 1.5 V to obtain the initial lithium extraction specific capacity.

[0096] 2. Initial coulombic efficiency

[0097] The initial coulombic efficiency is calculated according to the initial lithium extraction specific capacity and the initial lithium intercalation specific capacity, and the initial coulombic efficiency = initial lithium extraction specific capacity / initial lithium intercalation specific capacity.

[0098] 3. Capacity retention rate

[0099] The above battery is cycled by charging and discharging using a 0.2 C current, and the first cycle capacity C1 and the 500th cycle capacity C2 are recorded, and the capacity retention rate = C2 / C1.

[0100] 4. Test the rate performance of the battery core

[0101] 1) (25±2)℃ for 5 min; 2) 1C constant current discharge, cut-off voltage 2.5V; 3) rest for 30 min; 4) 1C constant current charge, cut-off voltage 4.25V, then constant voltage charge to current≤0.05C; 5) rest for 30 min; 6) XC constant current discharge to cut-off voltage 2.5V; 7) repeat 3) to 6) to get the discharge capacity of the battery with different rates. X is 2C, 3C, 5C in turn.

[0102] The test results are shown in Tables 1 and 2.

[0103] Table 1 Performance data of the porous carbon prepared by each example and the comparative example

[0104]

[0105] Table 2 Performance data of the test battery prepared by using the silicon-carbon negative electrode material of each example and the comparative example

[0106]

[0107] From Tables 1 and 2, it can be seen that when the raw material 1,3,5-tris(4-aminophenyl)benzene used in the present application is replaced by other compounds with similar structures (comparative examples 1-3), the performance of the prepared battery is seriously reduced, which may be because the 1,3,5-tris(4-aminophenyl)benzene has good symmetry and geometric structure of monomer.

[0108] Finally, it should be noted that: the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1, Preparation of carbon precursor: In an inert gas environment, 1,3,5-tris(4-aminophenyl)benzene is dissolved in a solvent in an ice-water bath and mixed with 4,4'-(hexafluoroisopropylene)diphthalic anhydride in an ice-water bath to react to obtain a hyperbranched polyamic acid solution, which is then placed in water to precipitate a polymer and dried to obtain polymer particles. The polymer particles are then placed in a mixture of excess acetic anhydride and pyridine for chemical imidization to obtain a powder, which is then heat-treated to obtain a hyperbranched polyimide. S2, Preparation of porous carbon: The carbon precursor obtained in step S1 is placed in a tube furnace, heated to 600-1000°C at 2-15°C / min under a N2 atmosphere, kept at this temperature for 2 hours, and then cooled naturally to room temperature under a N2 atmosphere to obtain a porous carbon material; S3, vapor phase silicon carbon deposition; Preferably, the gas phase silicon carbon deposition is specifically as follows: heating to 350-600°C under N2 conditions, then introducing a 20% by volume SiH4-N2 mixed gas, and maintaining at 350-600°C for 12-20h; then introducing a 10% by volume C2H2-N2 mixed gas, and maintaining at 350-600°C for 2-4h; finally, naturally cooling in an N2 atmosphere to obtain a silicon carbon negative electrode material.

2. The method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material according to claim 1, wherein: The molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 4,4'-(hexafluoroisopropylene)diphthalic anhydride is 1:1-1:2; Preferably, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 4,4'-(hexafluoroisopropylene)diphthalic anhydride is 1:1.1-1:1.35; Most preferably, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene to 4,4'-(hexafluoroisopropylene)diphthalic anhydride is 1:1.

31.

3. The method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material according to claim 1, wherein: In step S1, the solvent used in the reaction includes at least one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

4. The method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material according to claim 1, wherein: In step S1, the molar ratio of acetic anhydride to pyridine is 1:

1.

5. The method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material according to claim 1, wherein: In step S1, the chemical imidization time is 10-24 hours.

6. The method for preparing a hyperbranched polyimide-derived silicon-carbon negative electrode material according to claim 1, wherein: In step S1, the heat treatment is specifically: heat treating the obtained powder at 360-400° C. for 2-4 hours.

7. Silicon-carbon negative electrode material, characterized by: It is prepared by the method according to any one of claims 1 to 6.

8. Silicon-carbon negative electrode, characterized by: The silicon-carbon negative electrode comprises the silicon-carbon negative electrode material according to claim 7; Preferably, 90-91 wt% of the silicon-carbon negative electrode material according to claim 7, 4-5 wt% of carbon nanotubes, and 5 wt% of a binder are mixed with deionized water and prepared into a paste using a homogenizer; the paste is evenly scraped onto a copper foil, and then baked in a drying oven to obtain a silicon-carbon negative electrode.

9. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the silicon-carbon negative electrode according to claim 8.

10. An electrochemical device, characterized in that: The electrochemical device comprises the lithium-ion battery according to claim 9.

Images