A silicon-carbon negative electrode material and its preparation method and application

Abstract

A silicon-carbon anode material, its preparation method, and its application relate to the field of battery anode material preparation. The preparation method comprises: mixing a liquid silicon source and a liquid metal under inert gas protection to obtain a mixture; then mixing the mixture with porous carbon and heating it to 50-200°C for reaction; washing and drying the reaction product to obtain a silicon-carbon intermediate; and finally, coating the silicon-carbon intermediate with carbon to obtain the silicon-carbon anode material. The present invention prepares the silicon-carbon anode material through an environmentally friendly, low-cost, and easy-to-operate method, enriching the preparation routes of silicon-carbon anode materials.

Description

Technical Field

[0001] The present invention relates to the field of preparation of battery negative electrode materials, in particular to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] In many fields such as new energy vehicles, large-scale energy storage, and grid peak regulation, lithium-ion batteries have been widely used due to their advantages such as high operating voltage, long cycle life, and considerable energy density, which has greatly promoted the development of related industries. However, with the vigorous rise of the new energy vehicle industry and the continuous growth of large-scale energy storage demand, the development of lithium-ion batteries has also encountered bottlenecks. Currently, lithium-ion batteries are faced with the dual dilemma of difficult to break through energy density and high costs. These problems seriously restrict their in-depth application and performance improvement in a wider range of fields. Therefore, the research and development of high-capacity, low-cost electrode materials has become a necessary measure to further improve the energy density of lithium-ion batteries.

[0003] In the field of negative electrode materials for lithium-ion batteries, graphite, as the current mainstream negative electrode material, has reached a performance close to the limit of theoretical specific capacity. It is difficult to further improve the energy density of lithium-ion batteries through graphite negative electrode materials, and there is an urgent need to develop new high-specific capacity negative electrode materials.

[0004] In addition to carbon anode materials such as graphite, lithium titanate, silicon-based anode materials, and metal oxides / sulfides / phosphides are also under research. Silicon-based anode materials, due to their high specific capacity, the abundance of silicon in the Earth's crust (second only to oxygen), and their relatively low cost, have become a highly promising anode material research direction. However, silicon-based anode materials still face numerous challenges in practical applications. They produce large volume changes during charge and discharge, and their electrical conductivity is poor, resulting in low charge and discharge efficiency, unstable cycle performance, and insufficient rapid charge and discharge capabilities, severely hindering their commercialization. Currently, researchers typically employ techniques such as nano-processing of silicon-based materials and surface carbon coating to address these issues.

[0005] Silane cracking vapor deposition, an emerging technology for preparing nano-silicon-carbon, involves cracking silane in a high-temperature, inert gas environment and depositing it into the micropores of porous carbon materials. This technique utilizes the pores of the porous carbon to restrict the size of the silicon, providing excellent electrical conductivity. The resulting material exhibits advantages such as good cycling performance and high initial efficiency. However, this technology also has significant drawbacks. Silane gas is expensive and flammable, and is prone to violent spontaneous combustion upon contact with air. Summary of the Invention

[0006] The present invention provides a silicon-carbon negative electrode material and a preparation method and application thereof, so as to prepare the silicon-carbon negative electrode material through a green, low-cost and easy-to-operate method, thereby enriching the preparation path of the silicon-carbon negative electrode material.

[0007] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present invention is: a method for preparing a silicon-carbon negative electrode material, under the protection of an inert gas, mixing a liquid silicon source and a liquid metal to obtain a mixture, then mixing the mixture with porous carbon and heating it to 50-200°C for reaction, washing and drying the reaction product to obtain a silicon-carbon intermediate, and finally coating the surface of the silicon-carbon intermediate with carbon to obtain the silicon-carbon negative electrode material.

[0008] As a further optimization of the above technical solution, the liquid silicon source is one or more of trichlorosilane, silicon tetrachloride, hexachlorodisilane and silicon tetrabromide; the liquid metal is one or more of cesium, gallium, gallium-indium alloy, gallium-tin alloy, gallium-zinc alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy and sodium-potassium alloy.

[0009] As a further optimization of the above technical solution, the mass ratio of the liquid silicon source to the liquid metal in the mixture is 10:1-15.

[0010] As a further optimization of the above technical solution, the mass ratio of the mixture to the porous carbon added is 1:1-3.

[0011] As a further optimization of the above technical solution, the temperature when the liquid silicon source and the liquid metal are mixed, and the temperature when the mixture and the porous carbon are mixed is -30-20°C.

[0012] As a further optimization of the above technical solution, ultrasound or vacuum is assisted when the mixture is mixed with the porous carbon material.

[0013] As a further optimization of the above technical solution, the inert gas is one or more of nitrogen, argon and helium.

[0014] As a further optimization of the above technical solution, the surface carbon coating is one or more of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

[0015] The silicon-carbon negative electrode material is prepared by the above preparation method.

[0016] Application of silicon-carbon negative electrode materials in lithium-ion batteries.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention proposes a new method for preparing silicon-carbon negative electrode materials, constructs a more efficient and safer preparation path, and to a certain extent solves the problems of high energy consumption, long cycle, complex process, dangerous and expensive raw materials in the existing technology.

[0019] The present invention adopts a non-flammable and non-explosive liquid raw material system, which reduces production safety risks, simplifies the operation process, and improves process stability and controllability; at the same time, by shortening the process flow, reducing energy consumption, and effectively saving production costs.

[0020] The present invention controls the reaction between liquid silicon source and liquid metal in the pores of porous carbon material, innovatively uses porous carbon material as a nanoreactor, limits the size of nano-silicon in the reaction product, and washes away the salt generated by the reaction to provide space for volume expansion during the subsequent silicon charging and discharging process. The resulting silicon-carbon negative electrode material has electrochemical properties of high specific capacity, high charge and discharge efficiency, high rate, and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microscopic morphology of the silicon-carbon negative electrode material obtained in Example 1;

[0022] Figure 2 The X-ray spectrum of the silicon-carbon negative electrode material obtained in Example 1-4;

[0023] Figure 3 This is the Raman spectrum of the silicon-carbon negative electrode material obtained in Example 1;

[0024] Figure 4 This is an electronic image of the silicon-carbon negative electrode material obtained in Example 1;

[0025] Figure 5 for Figure 4 EDS pattern of carbon in the middle rectangular box;

[0026] Figure 6 for Figure 4 EDS image of silicon in the middle rectangular box;

[0027] Figure 7 Nitrogen adsorption and desorption curves of the porous carbon raw material and the prepared silicon-carbon negative electrode material used in Example 1;

[0028] Figure 8 The pore size distribution curves of the porous carbon raw material and the prepared silicon-carbon negative electrode material used in Example 1;

[0029] Figure 9 This is the charge and discharge curve of the silicon-carbon negative electrode material obtained in Example 1;

[0030] Figure 10 This is the cycle stability curve of the silicon-carbon negative electrode material obtained in Example 1;

[0031] Figure 11 This is the cycle stability curve of the silicon-carbon negative electrode material obtained in Example 2;

[0032] Figure 12This is the cycle stability curve of the silicon-carbon negative electrode material obtained in Example 3;

[0033] Figure 13 This is the cycle stability curve of the silicon-carbon negative electrode material obtained in Example 4. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further elaborated in detail below in conjunction with specific embodiments. Parts not described and disclosed in detail in the following embodiments of the present invention should be understood as existing technologies known or should be known to those skilled in the art.

[0035] The present invention discloses a method for preparing a silicon-carbon negative electrode material. Under low temperature and inert gas protection, a liquid silicon source and a liquid metal are mixed to obtain a mixture. The mixture is then mixed with porous carbon and heated to 50-200°C for reaction. The reaction product is washed and dried to obtain a silicon-carbon intermediate. Finally, the surface of the silicon-carbon intermediate is carbon-coated to obtain the silicon-carbon negative electrode material. The method specifically comprises the following steps:

[0036] S1. Under inert gas protection and at a temperature of -30-20°C, a liquid silicon source and a liquid metal are mixed in a mass ratio of 10:1-15 to obtain a liquid silicon source / liquid metal mixture. The liquid silicon source is one or more of trichlorosilane, silicon tetrachloride, hexachlorodisilane, and silicon tetrabromide; the liquid metal is one or more of cesium, gallium, a gallium-indium alloy, a gallium-tin alloy, a gallium-zinc alloy, a gallium-indium-tin alloy, a gallium-indium-tin-zinc alloy, and a sodium-potassium alloy; and the inert gas is one or more of nitrogen, argon, and helium.

[0037] S2. Continue to mix the liquid silicon source / liquid metal mixture and the porous carbon in a mass ratio of 1:1-3 under the protection of inert gas and a temperature of -30-20°C. During the mixing process, ultrasonic dispersion or vacuum treatment is used to promote the liquid silicon source / liquid metal mixture to fully diffuse into the pores of the porous carbon material.

[0038] The pore volume of the porous carbon used in the present invention is 0.5-0.9 cm 3 / g, a commercially available product. In practice, the amount of liquid silicon source / liquid metal mixture added needs to be controlled according to the pore volume of the porous carbon. If the addition amount is too large, although the pores of the porous carbon can be completely filled, the liquid silicon source / liquid metal mixture will accumulate excessively on the porous carbon surface, affecting the performance of the final product. If the addition amount is too small, the pore space of the porous carbon cannot be fully utilized, affecting the reaction efficiency and the performance indicators of the composite material. Therefore, rationally controlling the mass ratio of the liquid silicon source / liquid metal mixture to the porous carbon addition amount can effectively ensure product quality and performance.

[0039] S3. After the liquid silicon source / liquid metal mixture and porous carbon are mixed, they are heated to 50-200°C under the protection of inert gas to react, so that the liquid silicon source and liquid metal react in the pores of the porous carbon material to generate nano-silicon. In this process, the porous carbon material is used as a nanoreactor to limit the size of the nano-silicon in the reaction product.

[0040] S4. Add a washing solution, such as pure water or acid solution, to the product after the reaction, stir and wash it multiple times, separate and dry the washed solid to obtain a silicon-carbon intermediate.

[0041] As the liquid silicon source and liquid metal react chemically in the pores of the porous carbon, nano-silicon and salt products are generated. The salt substances are removed through a washing process. In this process, due to the spatial limitation of the porous carbon pores, the nano-silicon generated by the reaction is stably confined inside the pores and cannot escape; while the salt substances generated by the reaction can be dissolved in the washing solution and discharged with the washing solution.

[0042] On the one hand, the washing process can effectively remove salt substances in the pores to prevent them from occupying the pore space, reserving space for the volume expansion of silicon during the subsequent charging and discharging process; on the other hand, washing can also simultaneously remove the unreacted liquid silicon source and liquid metal remaining in the reaction system, ensuring the purity and performance stability of the prepared materials.

[0043] S5. Finally, the silicon-carbon intermediate is surface-coated with carbon by one or more methods: solid-phase carbon coating, liquid-phase carbon coating, or vapor-phase carbon coating. The surface-coated product is crushed to a particle size of 0.1-60 μm, preferably 1-25 μm, to obtain the silicon-carbon negative electrode material.

[0044] By carbon-coating the silicon-carbon intermediate, the outer surface of the porous carbon material can be effectively coated. If silicon particles are present on the outer surface of the porous carbon, these can also be coated simultaneously. Furthermore, the nano-silicon can be coated deep into the internal pores of the porous carbon. This surface carbon coating treatment significantly reduces the specific surface area, improving the processability of the prepared silicon-carbon anode material for lithium-ion batteries, facilitating material slurrying and coating, and enhancing electrochemical properties such as the initial efficiency.

[0045] Example 1

[0046] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0047] S1. In a nitrogen-protected reactor, the temperature was controlled at 0°C, 5 g of sodium-potassium alloy liquid metal and 10 g of silicon tetrachloride were added and vigorously stirred at a stirring speed of 500 rpm for 5 hours to obtain a liquid sodium-potassium alloy / silicon tetrachloride mixture;

[0048] S2, maintaining nitrogen protective atmosphere and controlling the environment at 0°C, adding 30 g of 0.7 cm pore volume to the liquid sodium potassium alloy / silicon tetrachloride mixture in step S1. 3 / g porous carbon, first stirred at 300 rpm for 2 hours to pre-mix, and then ultrasonicated at 300 W power for 3 hours under stirring to allow the sodium potassium alloy / silicon tetrachloride mixture to enter the pores of the porous carbon;

[0049] S3, controlling the temperature of the material obtained in step S2 to 60° C. and maintaining the temperature for 4 hours to allow the sodium-potassium alloy in the pores to undergo a reduction reaction with silicon tetrachloride to generate nano-silicon and sodium chloride / potassium chloride;

[0050] S4. The reaction system of step S3 was naturally cooled to room temperature. Under nitrogen protection, pure water was slowly added to the material system of step S3, and the mixture was stirred at a constant speed while controlling the temperature at 30°C. The mixture was then repeatedly washed with pure water for three times, and the solid matter was separated and dried to obtain a silicon-carbon intermediate.

[0051] S5. Place the silicon-carbon intermediate obtained in step S4 in a rotary kiln, introduce acetylene under nitrogen protection, maintain the temperature at 650° C. for 3 hours for gas-phase carbon coating, cool naturally, and crush to 1-25 μm to obtain the silicon-carbon negative electrode material.

[0052] Example 2

[0053] The overall steps of this embodiment are the same as those of embodiment 1, except that the silicon tetrachloride in step S1 of embodiment 1 is replaced with trichlorosilane in this embodiment.

[0054] Example 3

[0055] The overall steps of this embodiment are the same as those of embodiment 1, except that the silicon tetrachloride in step S1 of embodiment 1 is replaced with silicon tetrabromide in this embodiment.

[0056] Example 4

[0057] The overall steps of this embodiment are the same as those of Example 1, except that the silicon tetrachloride in step S1 of Example 1 is replaced with hexachlorodisilane in this embodiment.

[0058] Example 5

[0059] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0060] S1. In an argon-protected reactor, the temperature was controlled at 15° C., 10 g of liquid metal cesium and 15 g of hexachlorodisilane were added and stirred at 500 rpm for 3 hours to obtain a liquid cesium / hexachlorodisilane mixture;

[0061] S2, maintaining the argon protective atmosphere and controlling the environment at 15°C, add 40 g of 0.85 cm pore volume of the liquid cesium / hexachlorodisilane mixture in step S1. 3 / g porous carbon, first stirred at 300 rpm for 2 hours to pre-mix, and then ultrasonicated at 300 W power for 4 hours under stirring to allow the liquid cesium / hexachlorodisilane mixture to penetrate into the pores of the porous carbon;

[0062] S3, controlling the temperature of the material obtained in step S2 to 80° C. and maintaining the temperature for 6 hours to allow the metallic cesium in the pores to undergo a reduction reaction with hexachlorodisilane to generate nano-silicon and cesium chloride;

[0063] S4. The reaction system of step S3 was naturally cooled to room temperature. Under argon protection, pure water was slowly added to the material system of step S3, and the mixture was stirred at a constant speed while controlling the temperature at 30°C. The mixture was then repeatedly washed with pure water three times to remove by-products, and a silicon-carbon intermediate was isolated;

[0064] S5. Place the silicon-carbon intermediate obtained in step S4 in a rotary kiln, introduce acetylene under argon protection, and keep the temperature at 650°C for 3 hours to perform gas-phase carbon coating. Cool naturally and crush to 1-25 microns to obtain a silicon-carbon negative electrode material.

[0065] Example 6

[0066] The overall steps of this embodiment are the same as those of embodiment 5, except that the hexachlorodisilane in step S1 of embodiment 5 is replaced with silicon tetrachloride in this embodiment.

[0067] Example 7

[0068] The overall steps of this embodiment are the same as those of embodiment 5, except that the metal cesium in step S1 of embodiment 5 is replaced with gallium-indium-tin alloy in this embodiment.

[0069] Example 8

[0070] The overall steps of this embodiment are the same as those of embodiment 1, except that in this embodiment, steps S1-S3 are as follows:

[0071] S1. In a nitrogen-protected reactor, the temperature was controlled at -30°C, 5 g of sodium-potassium alloy liquid metal and 10 g of silicon tetrachloride were added and vigorously stirred at a stirring speed of 500 rpm for 5 hours to obtain a liquid sodium-potassium alloy / silicon tetrachloride mixture;

[0072] S2, maintaining a nitrogen protective atmosphere and controlling the environment at -30°C, adding 30 g of a 0.7 cm pore volume to the liquid sodium potassium alloy / silicon tetrachloride mixture in step S1. 3 / g porous carbon, first stirred at 300 rpm for 2 hours to pre-mix, and then ultrasonicated at 300 W power for 3 hours under stirring to allow the sodium potassium alloy / silicon tetrachloride mixture to enter the pores of the porous carbon;

[0073] S3, controlling the temperature of the material obtained in step S2 to 50° C. and maintaining the temperature for 4 hours to allow the sodium-potassium alloy in the pores to undergo a reduction reaction with silicon tetrachloride to generate nano-silicon and sodium chloride / potassium chloride;

[0074] Steps S4-S5 are the same as those in Example 1 and will not be described in detail.

[0075] Example 9

[0076] The overall steps of this embodiment are the same as those of embodiment 5, except that in this embodiment, steps S1-S3 are as follows:

[0077] S1. In an argon-protected reactor, the temperature was controlled at 20° C., 10 g of liquid metal cesium and 15 g of hexachlorodisilane were added and stirred at 500 rpm for 3 hours to obtain a liquid cesium / hexachlorodisilane mixture.

[0078] S2, maintaining an argon protective atmosphere and controlling the environment at 20°C, add 40 g of 0.85 cm pore volume of the liquid cesium / hexachlorodisilane mixture in step S1. 3 / g porous carbon, first stirred at 300 rpm for 2 hours to pre-mix, and then ultrasonicated at 300 W power for 4 hours under stirring to allow the liquid cesium / hexachlorodisilane mixture to penetrate into the pores of the porous carbon;

[0079] S3, controlling the temperature of the material obtained in step S2 to 200° C. and maintaining the temperature for 6 hours to allow the metallic cesium in the pores to undergo a reduction reaction with hexachlorodisilane to generate nano-silicon and cesium chloride;

[0080] Steps S4-S5 are the same as those in Example 5 and will not be described in detail.

[0081] The electrochemical performance of the silicon-carbon negative electrode material obtained in the above embodiment was tested in the following steps:

[0082] 1) Weigh a certain amount of silicon-carbon anode material and conductive agent Super-P, grind and mix them thoroughly, then dropwise add carboxymethyl cellulose aqueous solution (CMC, 1.5% solid content) and continue grinding and mixing to obtain a slurry. The weight ratio of silicon-carbon anode material to conductive agent Super-P and CMC is 93:2:5.

[0083] 3) The slurry is coated on copper foil, and then vacuum dried, rolled, and cut into pieces to prepare electrodes;

[0084] 4) A button cell battery was assembled using a lithium sheet as the counter electrode, a polyethylene / polypropylene composite separator, and a 1.0 mol / L LiPF6 electrolyte in ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1) with 10% fluoroethylene carbonate. The charge and discharge voltage was limited to 0.005–1.5 V.

[0085] Result analysis:

[0086] 1. Micromorphology Analysis

[0087] The microscopic morphology of the silicon-carbon negative electrode material obtained in Example 1 is as follows: Figure 1 As shown. Figure 1 It can be seen that the silicon-carbon negative electrode material prepared in Example 1 of the present invention maintains the morphology of porous carbon.

[0088] 2. XRD pattern analysis

[0089] The crystal structure of the silicon-carbon negative electrode material obtained in Examples 1-4 is as follows: Figure 2 shown.

[0090] from Figure 2 It can be seen that the silicon-carbon negative electrode materials obtained in each embodiment all present an amorphous structure, with broad peaks appearing at 20-30 degrees and 40-50 degrees, which are composite peaks of porous carbon (amorphous) and nanosilicon in the porous carbon pores, indicating that the nanosilicon in the pores is also in an amorphous state, which is beneficial to the cycle performance of the silicon-carbon negative electrode.

[0091] 3. Raman spectroscopy analysis

[0092] Figure 3 This is the Raman spectrum of the silicon-carbon negative electrode material prepared in Example 1, at 510 cm -1 The peaks on the left and right are characteristic peaks of elemental silicon, indicating the formation of nano-silicon; -1 and 1580 -1 The peaks that appear are attributed to the D peak and G peak of porous carbon.

[0093] 4. Material Micro-Area Composition Analysis

[0094] The present invention uses energy dispersive spectroscopy (EDS) to perform micro-area composition analysis on the prepared silicon-carbon negative electrode material. Figure 4 This is a microscopic image of the silicon-carbon negative electrode material prepared in Example 1. The area to be analyzed is selected by a rectangular frame, and the micro-area composition analysis of the material within the rectangular frame is performed. Figure 5 is the EDS diagram of carbon in the rectangular frame, Figure 6 This is the EDS image of silicon within the rectangular frame.

[0095] 5. Nitrogen adsorption-desorption curve and pore size distribution curve

[0096] Figure 7 The nitrogen adsorption / desorption curves of the porous carbon raw material used in Example 1 and the silicon-carbon negative electrode material (abbreviated as silicon-carbon in the figure) prepared in Example 1 are as follows: Figure 8 1 is the pore size distribution curve of the porous carbon raw material and the prepared silicon-carbon negative electrode material used in Example 1.

[0097] Depend on Figure 7 It can be seen that porous carbon raw materials have a larger nitrogen adsorption capacity because they have relatively abundant pores. Figure 8 It can also be seen that the porous carbon raw material has relatively abundant pores. After the preparation method of the present invention is used to react the liquid metal with the liquid silicon source, the nitrogen adsorption of the resulting silicon-carbon negative electrode material is greatly reduced, and the abundant pores are also significantly reduced. This is because the nano-silicon produced by the reaction of the liquid metal and the liquid silicon source fills the pores of the porous carbon.

[0098] According to calculation, the specific surface area of the porous carbon raw material used in Example 1 is 1760 m 2 / g, pore volume is 0.7cm 3 / g; the specific surface area of the silicon-carbon negative electrode material prepared by the reaction of liquid metal and liquid silicon source is 24 m 2 / g, pore volume is 0.05cm 3 The decrease in specific surface area and pore volume also indicates that the generated nano-silicon is in the pores of porous carbon.

[0099] 6. Charge and discharge curve

[0100] The charge and discharge curves of the silicon-carbon negative electrode material obtained in Example 1 are as follows: Figure 9 As shown, it can be seen that the obtained material has a specific capacity of up to 1780 mAh / g, an initial efficiency of more than 90%, and most of the discharge specific capacity is around 0.2 V, and the charge specific capacity is around 0.4 V, which is a typical charge and discharge curve of silicon-carbon negative electrode materials.

[0101] 7. Cyclic stability

[0102] The cycle stability curves of the silicon-carbon negative electrode materials obtained in Examples 1-4 are as follows: Figure 10-13 As shown, it can be seen that the silicon-carbon negative electrode material prepared by the method disclosed in the present invention has a capacity retention rate of about 90% after 100 cycles, showing excellent cycle stability. This is mainly due to the use of the technology of the present invention. The pores of the porous carbon become nano-reaction containers for liquid silicon source and liquid metal. The prepared nano-silicon is small in size and is physically constrained by the porous carbon. The volume change is small during the charge and discharge process, so the cycle stability is good.

[0103] The electrochemical test results of the batteries prepared using the silicon-carbon negative electrode materials prepared in Examples 1-4 are shown in Table 1:

[0104] Table 1

[0105] Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100-cycle capacity retention rate (%) Example 1 1870.5 11.2 91.3% 91.5 Example 2 1854.7 14.5 89.2% 88.4 Example 3 1680.2 13.1 88.7% 91.6 Example 4 1637.4 16.3 92.2% 95.9

[0106] The electrochemical test results of the battery prepared using the silicon-carbon negative electrode material prepared in Examples 5-6 are shown in Table 2:

[0107] Table 2

[0108] Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100-cycle capacity retention rate (%) Example 5 1635.8 12.7 91.2% 91.7 Example 6 1753.2 11.3 88.9% 92.1 Example 7 1562.3 10.6 89.3% 89.5

[0109] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: Under the protection of inert gas, a liquid silicon source and a liquid metal are mixed to obtain a mixture, and the mixture is then mixed with porous carbon and heated to 50-200°C for reaction for 4 hours or 6 hours. The reaction product is washed and dried to obtain a silicon-carbon intermediate, and finally the surface of the silicon-carbon intermediate is carbon-coated to obtain the silicon-carbon material; The liquid silicon source is one or more of trichlorosilane, silicon tetrachloride, hexachlorodisilane and silicon tetrabromide; the liquid metal is one or more of cesium, gallium, gallium-indium alloy, gallium-tin alloy, gallium-zinc alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy and sodium-potassium alloy; The mass ratio of the liquid silicon source to the liquid metal in the mixture is 10:1-15; The mass ratio of the mixture to the porous carbon addition amount is 1:1-3.

2. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: The temperature when the liquid silicon source and the liquid metal are mixed, and the temperature when the mixture and the porous carbon are mixed is -30-20°C.

3. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: The mixture is mixed with the porous carbon material with the aid of ultrasound or vacuum.

4. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: The inert gas is one or more of nitrogen, argon and helium.

5. The method for preparing a silicon-carbon negative electrode material according to claim 1, wherein: The surface carbon coating is one or more of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

6. The silicon-carbon negative electrode material prepared according to any one of claims 1 to 5.

7. Use of the silicon-carbon negative electrode material as claimed in claim 6 in a lithium-ion battery.

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