Silicon-carbon negative electrode material and preparation method therefor, and lithium ion battery

Abstract

A silicon-carbon negative electrode material and a preparation method therefor, and a lithium ion battery. The preparation method comprises: removing an X group in a silane coupling agent to form a first product, wherein the molecular formula of the silane coupling agent is formula (1), the first product is represented by formula (2), n is a positive integer greater than or equal to 1, the X group comprises at least one of an amino group, a chlorine group, a methyl group, a methoxy group and an ethoxy group, and a Y group comprises at least one of a vinyl group, an epoxy group, a methacryloyloxy group, a sulfhydryl group and a urea group; after the first product is gasified, forming silicon-oxygen-carbon composite nanoparticles in holes of porous carbon by means of a pyrolysis reaction and an adsorption-deposition reaction, wherein the silicon-oxygen-carbon composite nanoparticles comprise a silicon-oxygen compound and amorphous silicon, as well as at least one of amorphous carbon and ceramic-phase silicon carbide; and depositing a carbon coating layer on the surfaces of the silicon-oxygen-carbon composite nanoparticles. The method can reduce the production cost and is suitable for industrial application.

Description

Silicon-carbon negative electrode material and preparation method thereof, and lithium-ion battery Technical Field

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

[0002] As the demand for energy density in lithium-ion batteries increases, existing graphite anodes are unlikely to meet future demands. Compared to commercial graphite electrodes, silicon electrodes have a theoretical specific capacity 10 times greater, at 4200 mM / g. However, silicon electrodes undergo significant volume changes (>300%) during lithium insertion and removal, leading to particle fragmentation and poor cycling stability.

[0003] Various studies have shown that reducing the particle size of silicon electrodes to nanoscale and making carbon coatings on nano-silicon to form nano-silicon-based composite materials is a method to inhibit the particle breakage of silicon electrodes and improve the cycle stability. However, the tap density, coulomb efficiency and cost of nano-silicon-based composite materials are low, which inhibit their industrialization. In contrast, micro-silicon-based composite materials, especially modified micro-silicon-based composite materials, are more favored by the industry. The modification method of the micro-silicon-based composite material includes coating amorphous carbon or graphene on the silicon surface to improve its stability. However, there is still a lack of low-cost methods that can produce micro-silicon-based composite materials with high electrochemical performance on a large scale.

[0004] Summary of the Invention

[0005] One aspect of the present application provides a method for preparing a silicon-carbon negative electrode material, comprising: removing the X group in a silane coupling agent to form a first product, wherein the molecular formula of the silane coupling agent is The first product is wherein n is a positive integer greater than or equal to 1, the X group includes at least one of an amino group, a chloro group, a methyl group, a methoxy group, and an ethoxy group, and the Y group includes at least one of a vinyl group, an epoxy group, a methacryloxy group, a mercapto group, and a urea group; after gasifying the first product, silicon-oxygen-carbon composite nanoparticles are formed in the pores of the porous carbon through a cracking reaction and an adsorption deposition reaction, wherein the silicon-oxygen-carbon composite nanoparticles include silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide; and a carbon coating layer is deposited on the surface of the silicon-oxygen-carbon composite nanoparticles.

[0006] In some embodiments of the present application, the silane coupling agent includes at least one of 3-(methacryloyloxy)propyltrimethoxysilane, 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.

[0007] In some embodiments of the present application, a heat treatment process is used to remove the X group in the silane coupling agent, and the heat treatment process is performed in an inert atmosphere at a temperature of 500° C. to 800° C.

[0008] In some embodiments of the present application, before removing the X group in the silane coupling agent by a heat treatment process, the preparation method further comprises: removing impurities in the silane coupling agent at a temperature of 100° C. to 200° C.

[0009] In some embodiments of the present application, when the X group is an amino group or a chloro group, the heat treatment process is carried out at a temperature of 500°C to 600°C; when the X group is a methyl group, the heat treatment process is carried out at a temperature of 600°C to 700°C; and when the X group is a methoxy group or an ethoxy group, the heat treatment process is carried out at a temperature of 700°C to 800°C.

[0010] In some embodiments of the present application, when the X group is an amino group or a chloro group, a hydrolysis process is used to remove the X group in the silane coupling agent.

[0011] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles account for 40% to 50% of the silicon-carbon negative electrode material by mass.

[0012] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles fill 40% to 70% of the volume of the pores.

[0013] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles include, by mass percentage, 80% to 95% silicon oxides, 5% to 10% amorphous silicon, 0% to 6% amorphous carbon, and 0% to 4% ceramic phase silicon carbide.

[0014] In some embodiments of the present application, the reaction temperature for forming silicon-oxygen-carbon composite nanoparticles in the pores of porous carbon through the cracking reaction and the adsorption deposition reaction is 900° C. to 1000° C.

[0015] In some embodiments of the present application, the specific surface area of ​​the porous carbon is 1500 to 2500 m 2 / g, the volume of the pores is 0.6-1.5g / m 3 .

[0016] In some embodiments of the present application, in the pores, the volume of micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2 nm, and the pore diameter of the mesopores is 2 nm to 50 nm.

[0017] In some embodiments of the present application, the process of depositing a carbon coating layer on the surface of the silicon-oxygen-carbon composite nanoparticles includes: depositing a first carbon coating layer on the surface of the silicon-oxygen-carbon composite nanoparticles; and then depositing a second carbon coating layer on the surface of the first carbon coating layer, wherein the first carbon coating layer is an amorphous carbon layer grown in an orderly manner, and the second carbon coating layer has a convex-concave structure on the surface.

[0018] On the other hand, the present application also provides a silicon-carbon negative electrode material, including: porous carbon, the porous carbon including pores, silicon-oxygen-carbon composite nanoparticles formed in the pores, the silicon-oxygen-carbon composite nanoparticles including silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide; the surface of the silicon-oxygen-carbon composite nanoparticles has a carbon coating layer.

[0019] In some embodiments of the present application, the specific surface area of ​​the porous carbon is 1500 to 2500 m 2 / g, the volume of the pores is 0.6-1.5g / m 3 .

[0020] In some embodiments of the present application, in the pores, the volume of micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2 nm, and the pore diameter of the mesopores is 2 nm to 50 nm.

[0021] In some embodiments of the present application, the carbon coating layer includes: a first carbon coating layer coating the surface of the silicon-oxygen-carbon composite nanoparticles; a second carbon coating layer coating the surface of the first carbon coating layer, the first carbon coating layer is an amorphous carbon layer grown in an orderly manner, and the second carbon coating layer has a convex-concave structure on the surface.

[0022] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles fill 40% to 70% of the volume of the pores.

[0023] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles include, by mass percentage, 80% to 95% silicon oxides, 5% to 10% amorphous silicon, 0% to 6% amorphous carbon, and 0% to 4% ceramic phase silicon carbide.

[0024] An embodiment of the present application further provides a lithium-ion battery, comprising a negative electrode, wherein the negative electrode comprises any one of the silicon-carbon negative electrode materials described in the embodiment of the present application.

[0025] The present application provides a silicon-carbon negative electrode material and a preparation method thereof, using a silane coupling agent as a silicon source. Since the silane coupling agent has low cost and high safety, the preparation method can reduce production costs and is suitable for industrial applications.

[0026] The preparation method of the silicon-carbon negative electrode material described in the embodiment of the present application uses a silane coupling agent as a silicon source, and adopts a cracking and adsorption deposition method to deposit uniformly distributed silicon-oxygen-carbon composite nanoparticles in the pores of a porous carbon matrix. The silicon-oxygen-carbon composite nanoparticles are silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide. The amorphous carbon has good conductivity, and the pores in the porous carbon and the ceramic phase silicon carbide can effectively alleviate the volume expansion of silicon oxides and amorphous silicon during the charge and discharge cycle. The lithium-ion battery made of the silicon-carbon negative electrode material has better conductivity and higher first charge capacity and volume share. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The following figures describe in detail exemplary embodiments disclosed in this application. Identical reference numerals denote similar structures in several views of the drawings. Those skilled in the art will appreciate that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of this application. Other embodiments may also achieve the same inventive intent as described in this application. It should be understood that the drawings are not drawn to scale. Among them:

[0028] FIG1 is a flow chart of a method for preparing a silicon-carbon negative electrode material according to an embodiment of the present application;

[0029] FIG2 is a schematic structural diagram of a silicon-carbon negative electrode material according to an embodiment of the present application;

[0030] FIG3 is a schematic structural diagram of the equipment used in the method for preparing the silicon-carbon negative electrode material according to an embodiment of the present application;

[0031] FIG4 is a scanning electron microscope image of the silicon-carbon negative electrode material according to an embodiment of the present application. DETAILED DESCRIPTION

[0032] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content of this application. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but is intended to be of the widest scope consistent with the claims.

[0033] 1 , the method for preparing the silicon-carbon negative electrode material according to an embodiment of the present application includes the following steps:

[0034] Step S1: removing the X group in the silane coupling agent to form a first product, wherein the molecular formula of the silane coupling agent is The first product is Wherein n is a positive integer greater than or equal to 1, the X group includes at least one of amino, chloro, methyl, methoxy and ethoxy, and the Y group includes at least one of vinyl, epoxy, methacryloxy, mercapto and urea.

[0035] In some embodiments of the present application, the silane coupling agent includes at least one of 3-(methacryloyloxy)propyltrimethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

[0036] In some embodiments of the present application, when the X group is an amino group or a chloro group, a hydrolysis process is used to remove the X group in the silane coupling agent. The hydrolysis process includes: adding the silane coupling agent to an aqueous solution, hydrolyzing the amino group or the chloro group in the silane coupling agent in the aqueous solution, and drying the hydrolyzed product to remove the water therein to form the first product.

[0037] In some embodiments of the present application, a heat treatment process is used to remove the X group in the silane coupling agent. The heat treatment process includes: performing the heat treatment in an inert atmosphere at a temperature of 500°C to 800°C to form a first product mainly including Si, O, and C elements. Specifically, the heat treatment process includes: heating the silane coupling agent to the fracture temperature of the X group under the protection of an inert gas, and heat treating for a specific time to completely remove the X group, thereby forming the first product. The inert gas is, for example, argon, and the heat treatment time is, for example, 3 hours to 5 hours.

[0038] Since silane coupling agents usually contain impurities such as moisture, in some embodiments of the present application, before using a heat treatment process to remove the X group in the silane coupling agent, the preparation method further includes: removing impurities in the silane coupling agent at a temperature of 100° C. to 200° C.

[0039] Since the X group is closely related to -[CH2] n - is bonded in the form of a chemical bond. Different heat treatment temperatures are required for different X groups to control the breakage of the chemical bond. In some embodiments of the present application, when the X group is an amino group or a chloro group, the heat treatment process is carried out at a temperature of 500°C to 600°C, and the CN bond will break at 500°C to 600°C; when the X group is a methyl group, the heat treatment process is carried out at a temperature of 600°C to 700°C, and the CC bond will break at 600°C to 700°C; and when the X group is a methoxy group or an ethoxy group, the heat treatment process is carried out at a temperature of 700°C to 800°C, and the CO bond will break at 700°C to 800°C.

[0040] Since the presence of the X group can destroy the structure of the porous carbon matrix in the subsequent process on the one hand, and occupy the pores of the porous carbon on the other hand, the silicon-oxygen-carbon composite nanoparticles generated in the subsequent process cannot enter the interior of the pores, thereby deteriorating the cycle performance of the generated silicon-carbon negative electrode material, it is necessary to remove the X group first.

[0041] Step S2: After gasifying the first product, forming silicon-oxygen-carbon composite nanoparticles in the pores of the porous carbon through a cracking reaction and an adsorption deposition reaction, wherein the silicon-oxygen-carbon composite nanoparticles include silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide;

[0042] In an embodiment of the present application, the temperature for vaporizing the first product is 900°C to 1000°C. The process of vaporizing the first product can be performed in an evaporation chamber. After vaporizing the first product, the vaporized first product is introduced into a deposition chamber, wherein porous carbon is placed in the deposition chamber. The vaporized first product undergoes a cracking reaction in the deposition chamber to form cracked products. The cracked products undergo an adsorption and deposition reaction in the pores of the porous carbon to form silicon-oxygen-carbon composite nanoparticles. The silicon-oxygen-carbon composite nanoparticles include silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic silicon carbide. In some embodiments, the silicon-oxygen-carbon composite nanoparticles include silicon oxides, amorphous silicon, amorphous carbon, and ceramic silicon carbide. In other embodiments, the silicon-oxygen-carbon composite nanoparticles include silicon oxides, amorphous silicon, and amorphous carbon. The silicon-oxygen-carbon composite nanoparticles may also include silicon oxides, amorphous silicon, and ceramic silicon carbide.

[0043] In some embodiments of the present application, the deposition time of the cracking reaction and adsorption deposition reaction to form silicon-oxygen-carbon composite nanoparticles in the pores of porous carbon is 1.5 hours to 4.5 hours, and the deposition temperature is 900°C to 1000°C. Optionally, the deposition time is 2.5 hours, and the deposition temperature is, for example, 940°C, 960°C and 990°C.

[0044] In the embodiment of the present application, the specific surface area of ​​the porous carbon is 1500-2500m 2 / g, the volume of the pores is 0.6-1.5g / m 3 , in the pores, the volume of micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2nm, and the pore diameter of the mesopores is 2nm to 50nm. The larger specific surface area and larger pore volume of the porous carbon allow more silicon-oxygen-carbon composite nanoparticles to be deposited in the porous carbon, so as to improve the reversible capacity, charge-discharge cycle performance and conductivity of the formed silicon-carbon negative electrode material. The micropores limit the particle size of the silicon oxides, amorphous silicon, amorphous carbon and ceramic phase silicon carbide particles formed in the pores.

[0045] At a deposition temperature of 900°C to 1000°C, the first product first undergoes a cracking reaction, wherein the CC bond and OC bond in the first product are first broken, and then the Si-O bond and Si-C bond are broken, and the molecules formed by the breakage enter the pores of the porous carbon through capillary adsorption.

[0046] During the cracking reaction, although the C—H bonds and Si—H bonds in the first product are also broken to form H ions, the H ions can react with oxidizing substances in the environment to generate water vapor after cracking, and the water vapor leaves the reaction chamber along with the reaction by-products.

[0047] The C atoms generated during the cracking reaction are adsorbed and deposited in the pores to form amorphous carbon. The amorphous carbon can greatly improve the conductivity of the silicon-carbon negative electrode material.

[0048] The Si and O atoms generated during the cracking reaction are also adsorbed and deposited in the pores. Some of the Si atoms will nucleate and grow in the form of amorphous silicon, while other Si atoms will combine with O atoms and be deposited in the pores in the form of silicon oxides. The greater the amount of amorphous silicon and silicon oxides deposited as the silicon-carbon negative electrode material, the higher the gram capacity of the silicon-carbon negative electrode material. The theoretical gram capacity of silicon is 4200mAh / g, and the theoretical gram capacity of the silicon oxide is 2600mAh / g.

[0049] At the end of the adsorption-deposition reaction, some of the amorphous carbon atoms previously deposited in the pores react with some of the amorphous silicon atoms to form ceramic-phase silicon carbide (SiC). This ceramic-phase silicon carbide has high hardness and is evenly distributed within the pores. During the charge-discharge cycle of the silicon-carbon anode material, the insertion and extraction of lithium ions causes the silicon-carbon anode material to expand in volume. This ceramic-phase silicon carbide can suppress and mitigate this expansion.

[0050] In the embodiment of the present application, the first product can be controlled by controlling the deposition temperature of the cracking and adsorption deposition reaction. The breaking of chemical bonds in the porous carbon thereby controls the mass percentage of amorphous carbon, amorphous silicon, silicon oxide compounds, and ceramic phase silicon carbide formed in the pores of the porous carbon. As the reaction time of the cracking and adsorption deposition reactions increases, the mass percentage of amorphous carbon, amorphous silicon, silicon oxide compounds, and ceramic phase silicon carbide formed in the pores of the porous carbon also changes. For example, increasing the deposition temperature and reaction time will reduce the content of the amorphous carbon.

[0051] In other embodiments, the content of each molecular group and the length of the carbon chain of the first product can be controlled by selecting the type of the silane coupling agent, thereby controlling the mass percentage of amorphous carbon, amorphous silicon, silicon oxides and ceramic phase silicon carbide formed in the pores of the porous carbon.

[0052] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles comprise, by mass percentage, 80% to 95% silicon oxide, 5% to 10% amorphous silicon, 0% to 6% amorphous carbon, and 0% to 4% ceramic silicon carbide. In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles comprise 90% silicon oxide, 5% amorphous silicon, 3% amorphous carbon, and 2% ceramic silicon carbide. Alternatively, in other embodiments, the silicon-oxygen-carbon composite nanoparticles comprise 88% silicon oxide, 7% amorphous silicon, 2% amorphous carbon, and 3% ceramic silicon carbide.

[0053] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles account for 40% to 50% of the silicon-carbon negative electrode material by mass.

[0054] As the cracking and adsorption deposition reactions continue, the silicon-oxygen-carbon composite nanoparticles formed in the pores continue to nucleate and grow until they fill the entire pore. Since most of the silicon-oxygen-carbon composite nanoparticles in the embodiments of the present application are formed in micropores, more than 80% of the silicon-oxygen-carbon composite nanoparticles have a cross-sectional diameter of less than or equal to 2 nm. The length of the silicon-oxygen-carbon composite nanoparticles varies with the length of the pores. In some embodiments of the present application, the length of the silicon-oxygen-carbon composite nanoparticles accounts for 40-70% of the length of the pores.

[0055] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles fill 40% to 70% of the volume of the pores. If the proportion of the silicon-oxygen-carbon composite nanoparticles filling the pore volume is too low, the charge and discharge capacity of the silicon-carbon negative electrode material will be reduced. However, such a low proportion means that the unfilled volume in the pores is large, which can effectively alleviate the volume expansion of the silicon-carbon negative electrode material. If the proportion of the silicon-oxygen-carbon composite nanoparticles filling the pore volume is too high, for example, all the solvent in the pores is completely filled by the silicon-oxygen-carbon composite nanoparticles, and even some of the silicon-oxygen-carbon composite nanoparticles are deposited on the porous carbon surface, then during the slurry process of making the battery negative electrode of the silicon-carbon negative electrode material, the amorphous silicon deposited on the porous carbon surface will generate bubbles in the water system. Moreover, after the silicon-carbon negative electrode material is made into a battery cell, during the electrochemical cycle, the amorphous silicon deposited on the porous carbon surface will expand in volume, and the part that undergoes the volume expansion will not be supported by the carbon skeleton of the porous carbon, making the structure of the battery cell more prone to rupture.

[0056] In the embodiment of the present application, as shown in FIG3 , the process of removing the X group in the silane coupling agent by a heat treatment process and the process of vaporizing the first product can be carried out in an evaporation chamber, and the cracking and adsorption deposition reaction can be carried out in the deposition chamber. The evaporation chamber and the deposition chamber can be connected by a first pipe 10. The first pipe 10 can also be connected to a second pipe 11 and a third pipe 12. The second pipe 11 and the third pipe 12 are mutually conductive at the connection point with the first pipe 10. A three-way switch 13 is provided at the connection point, and a one-way valve 14 is provided on the third pipe 12. After the first product is vaporized in the evaporation chamber, the switch of the three-way switch 13 is set at point B and the one-way valve is closed. Then, the vaporized first product is passed from the evaporation chamber into the deposition chamber. Porous carbon is placed in the deposition chamber. The porous carbon reacts with the vaporized first product by chemical vapor deposition to generate the silicon-oxygen-carbon composite nanoparticles. By controlling the opening and closing of the three-way switch, the flow rate of the first gasified product entering the deposition chamber is adjusted, thereby adjusting the mass percentages of carbon-oxygen and silicon in the silicon-oxygen-carbon composite nanoparticles.

[0057] When a heat treatment process is used within the evaporation chamber to remove the X groups from the silane coupling agent, the three-way switch 13 is opened to point A and the one-way valve is closed. Impurity groups generated by decomposition during the heat treatment process are then discharged through the second conduit 11. If the deposition reaction to form the carbon coating layer also occurs within the deposition chamber, the one-way valve is opened and the three-way switch is opened to point C during deposition of the carbon coating layer. The carbon source gas for forming the carbon coating layer enters the deposition chamber through the third conduit 12 for coating.

[0058] Step S3: depositing a carbon coating layer on the surface of the silicon-oxygen-carbon composite nanoparticles.

[0059] In the embodiments of the present application, the reaction to form the carbon coating layer can be carried out in a chemical vapor deposition apparatus or in the deposition chamber shown in FIG3 . The raw material gas for forming the carbon coating layer is a carbon-containing gas, such as at least one of methane, acetylene, or propane. The raw material gas flow rate is 1 to 5 L / min, the reaction temperature is 600 to 900°C, and the reaction time is 1 to 10 hours.

[0060] In one embodiment of the present application, the process of depositing a carbon coating layer on the surface of the silicon-oxygen-carbon composite nanoparticles includes: depositing a first carbon coating layer on the surface of the silicon-oxygen-carbon composite nanoparticles; and then depositing a second carbon coating layer on the surface of the first carbon coating layer, wherein the first carbon coating layer is an amorphous carbon layer grown in an orderly manner, and the second carbon coating layer has a convex-concave structure on the surface.

[0061] In one embodiment of the present application, a first carbon coating layer is first deposited on the surface of silicon-oxygen-carbon composite nanoparticles. For example, acetylene is first used as the raw material gas for CVD reaction, and the reaction conditions are: the flow rate of acetylene gas is 1 to 3 L / min, the reaction temperature is 600-700°C, and the reaction time is 1 to 5 hours; then a second carbon coating layer is deposited on the surface of the first carbon coating layer. For example, methane is used as the raw material gas for CVD reaction, and the reaction conditions are: the flow rate of methane gas is 1 to 3 L / min, the reaction temperature is 600-900°C, and the reaction time is 1 to 10 hours.

[0062] In an embodiment of the present application, a first carbon coating layer and a second carbon coating layer are deposited on the surface of silicon-oxygen-carbon composite nanoparticles. On the one hand, the first carbon coating layer and the second carbon coating layer formed on the surface of the silicon-oxygen-carbon composite nanoparticles are carbon layers with different structures. The first carbon coating layer can provide a uniform coating layer and structure, and the second carbon coating layer provides a rich conductive network.

[0063] An embodiment of the present application also provides a silicon-carbon negative electrode material, including: porous carbon, the porous carbon including pores, silicon-oxygen-carbon composite nanoparticles formed in the pores, the silicon-oxygen-carbon composite nanoparticles including silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide; the surface of the silicon-oxygen-carbon composite nanoparticles has a carbon coating layer.

[0064] FIG2 is a schematic diagram of the structure of the silicon-carbon anode material formed in an embodiment of the present application. As can be seen from the figure, the silicon-carbon anode material skeleton is a porous carbon 110. Silicon oxide 113, amorphous silicon 114, amorphous carbon 115, and ceramic silicon carbide 116 are deposited within the pores 111 of the porous carbon 110. The carbon coating layer 112 coats the surface of the silicon-oxygen-carbon composite nanoparticles. The silicon oxide 113, amorphous silicon 114, amorphous carbon 115, and ceramic silicon carbide 116 are relatively evenly distributed within the pores 111.

[0065] In the embodiment of the present application, the specific surface area of ​​the porous carbon is 1500-2500m 2 / g, the volume of the pores is 0.6-1.5g / m 3 In the pores, the volume of micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2nm, and the pore diameter of the mesopores is 2nm to 50nm.

[0066] In an embodiment of the present application, the carbon coating layer includes: a first carbon coating layer coating the surface of the silicon-oxygen-carbon composite nanoparticles; a second carbon coating layer coating the surface of the first carbon coating layer, the first carbon coating layer is an amorphous carbon layer grown in an orderly manner, and the second carbon coating layer has a convex-concave structure on the surface.

[0067] In the embodiment of the present application, the pores are not completely filled, and the silicon-oxygen-carbon composite nanoparticles fill 40% to 70% of the volume of the pores.

[0068] In some embodiments of the present application, the silicon-oxygen-carbon composite nanoparticles include, by mass percentage, 80% to 95% silicon oxides, 5% to 10% amorphous silicon, 0% to 6% amorphous carbon, and 0% to 4% ceramic phase silicon carbide.

[0069] The present application provides a silicon-carbon negative electrode material and a preparation method thereof, using a silane coupling agent as a silicon source. Since the silane coupling agent has low cost and high safety, the preparation method can reduce production costs and is suitable for industrial applications.

[0070] The preparation method of the silicon-carbon negative electrode material described in the embodiment of the present application uses a silane coupling agent as a silicon source, and adopts a cracking and adsorption deposition method to deposit uniformly distributed silicon-oxygen-carbon composite nanoparticles in the pores of a porous carbon matrix. The silicon-oxygen-carbon composite nanoparticles are silicon oxides and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide. The amorphous carbon has good conductivity, and the pores in the porous carbon and the ceramic phase silicon carbide can effectively alleviate the volume expansion of silicon oxides and amorphous silicon during the charge and discharge cycle. The lithium-ion battery made of the silicon-carbon negative electrode material has better conductivity and higher first charge capacity and volume share.

[0071] The present application also provides a lithium-ion battery, which includes a negative electrode, and the negative electrode includes the silicon-carbon negative electrode material described in any embodiment.

[0072] This application does not limit the preparation method of the negative electrode sheet. This embodiment only provides an implementable preparation method: a mixture of the silicon-carbon negative electrode material, binder, and conductive agent is homogenized and coated on copper foil, vacuum dried, and rolled to produce the negative electrode sheet. The mass ratio of the silicon-carbon negative electrode material, binder, and conductive agent can be 70:20:10. The conductive agent can be conductive carbon black, the binder can be any commercially available binder for lithium-ion batteries, and the dispersant can be deionized water.

[0073] The present application does not limit the preparation method of the lithium-ion battery. This embodiment is only one possible preparation method: a 1 mol / L LiPF6 mixed solvent is used as the electrolyte, a polypropylene microporous membrane is used as the diaphragm, and a metal lithium sheet is used as the counter electrode. The silicon-carbon negative electrode material prepared in any embodiment of the present application is prepared into the negative electrode of the lithium-ion battery, and the button cells are assembled in an inert gas glove box system filled with argon to prepare the lithium-ion battery.

[0074] Example 1:

[0075] Executing step S1, removing impurities from the silane coupling agent using a heat treatment process, first placing 100 g of the silane coupling agent (3-aminopropyltriethoxysilane) in an evaporation chamber, heating to 700° C. in an argon atmosphere to remove the amino group in the 3-aminopropyltriethoxysilane, and reacting for 3 hours under constant temperature conditions to obtain a first product;

[0076] Executing step S2: placing 100 g of porous carbon in the deposition chamber, raising the temperature of the evaporation chamber to 900° C., vaporizing and evaporating the first product, and then passing it into the deposition chamber, setting the temperature in the deposition chamber to the same as the evaporation temperature of the evaporation chamber as the deposition temperature, and allowing a vapor deposition reaction to occur in the deposition chamber for 2.5 hours to obtain silicon-oxygen-carbon composite nanoparticles;

[0077] Execute step S3: introduce acetylene into the deposition chamber, the acetylene flow rate is 0.5 L / min, the coating temperature is 600° C., and the coating time is 3 hours to obtain a silicon-carbon negative electrode material coated with a carbon coating layer.

[0078] Referring to Figure 4, which shows an SEM image of a cross-section of the silicon-carbon anode material formed using the method of an embodiment, it can be seen that there are partially unfilled pores within the silicon-oxygen-carbon composite nanoparticles, indicating that the porous carbon is not completely filled. These incomplete pores can mitigate the volume expansion of the silicon-carbon anode material during the charge-discharge cycle. Furthermore, the pores contain silicon-oxygen-carbon composite nanoparticles, which include various types of microparticles, such as amorphous carbon, amorphous silicon, silicon oxide compounds, and ceramic silicon carbide.

[0079] Example 2

[0080] Compared with Example 1, the mass of the silane coupling agent (3-aminopropyltriethoxysilane) was changed to 50 g.

[0081] Example 3

[0082] Compared with Example 1, the mass of the silane coupling agent (3-aminopropyltriethoxysilane) was changed to 200 g.

[0083] Example 4

[0084] Compared to Example 1, the temperature in step S1 was adjusted to 400°C.

[0085] Example 5

[0086] Compared to Example 1, the temperature in step S1 was adjusted to 1000°C.

[0087] Example 6

[0088] Compared with Example 1, the reaction time in step S1 was adjusted to 1 h.

[0089] Example 7

[0090] Compared with Example 1, the reaction time in step S1 was adjusted to 5 h.

[0091] Example 8

[0092] Compared with Example 1, the deposition temperature in step S2 was adjusted to 700°C.

[0093] Example 9

[0094] Compared with Example 1, the deposition temperature in step S2 was adjusted to 1100°C.

[0095] Example 10

[0096] Compared with Example 1, the deposition time in step S2 was adjusted to 1 h.

[0097] Example 11

[0098] Compared with Example 1, the deposition time in step S2 was adjusted to 4 h.

[0099] Example 12

[0100] Compared with Example 1, the coating temperature in step S3 was adjusted to 500°C.

[0101] Example 13

[0102] Compared with Example 1, the coating temperature in step S3 was adjusted to 700°C.

[0103] Example 14

[0104] Compared with Example 1, the coating time in step S3 was adjusted to 1 h.

[0105] Example 15

[0106] Compared with Example 1, the coating time in step S3 was adjusted to 5 h.

[0107] Example 16

[0108] Compared with Example 1, the flow rate of acetylene in step S3 was adjusted to 0.1 L / min.

[0109] Example 17

[0110] Compared with Example 1, the flow rate of acetylene in step S3 was adjusted to 1 L / min.

[0111] Example 18

[0112] Step S1: Decontamination of the silane coupling agent using a hydrolysis method. 100 ml of the silane coupling agent (3-aminopropyltriethoxysilane) was placed in an aqueous solution and stirred at high speed for 1 hour to allow for complete hydrolysis and removal of the amino groups in the 3-aminopropyltriethoxysilane. The water in the aqueous solution was then evaporated to obtain a first product. The remaining steps were the same as in Example 1.

[0113] Example 19

[0114] Compared to Example 1, the temperature in step S1 was adjusted to 500°C.

[0115] Example 20

[0116] Compared to Example 1, the temperature in step S1 was adjusted to 600°C.

[0117] Example 21

[0118] Compared with Example 1, the silane coupling agent in step S1 was adjusted to 3-(methacryloyloxy)propyltrimethoxysilane.

[0119] Example 22

[0120] Compared with Example 1, the silane coupling agent in step S1 was adjusted to 3-aminopropyltrimethoxysilane.

[0121] Table 1 shows the effect of different masses of silane coupling agents on the electrochemical performance of the generated silicon-carbon negative electrode material after being made into a lithium-ion battery. When all other conditions are exactly the same, only the mass of the silane coupling agent (3-aminopropyltriethoxysilane) as a reactant is changed, and the difference in electrochemical performance of the generated silicon-carbon negative electrode material after being made into a lithium-ion battery is observed. As can be seen from Table 1, the greater the mass of the silane coupling agent, the higher the corresponding first charge capacity and first coulombic efficiency of the lithium-ion battery made from the generated silicon-carbon negative electrode material. This shows that the greater the mass of the silane coupling agent, the more silicon-oxygen-carbon composite nanoparticles will be generated. However, the mass of the silane coupling agent as a reactant cannot be too large. When the mass of the silane coupling agent is too large, after the pores in the porous carbon are filled, the generated silicon-oxygen-carbon composite nanoparticles will be deposited on the surface of the porous carbon. The silicon-oxygen-carbon composite nanoparticles deposited on the surface of the porous carbon will have greater activity, and volume expansion will occur during the charge and discharge process of the lithium-ion battery, and the volume expansion will lead to poor cycle performance.

[0122] Table 1. Effects of different silane coupling agent masses on the electrochemical performance of lithium-ion batteries made from silicon-carbon anode materials

[0123] The capacity retention rate after 200 cycles in this application refers to the capacity retention rate of a lithium-ion battery prepared from the silicon-carbon negative electrode material prepared in the example after 200 charge and discharge cycles. When the content of silicon oxides and amorphous silicon in the silicon-carbon negative electrode material is high, the volume expansion of the lithium-ion battery during the charge and discharge cycle will increase, resulting in a deterioration in the charge and discharge cycle performance of the lithium-ion battery. When the amount of silicon-oxygen-carbon composite nanoparticles deposited in the pores increases, the volume of the pores not filled with silicon-oxygen-carbon composite nanoparticles decreases, and the charge and discharge cycle performance of the lithium-ion battery deteriorates.

[0124] Table 2 shows the effects of using different reaction temperatures and reaction times in step S1, as well as different process methods (thermal decomposition or hydrolysis) to remove the amino group from 3-aminopropyltriethoxysilane to obtain the first product, on the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery. With all other conditions remaining identical, only the temperature and time of the thermal decomposition process are varied to see differences in the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery.

[0125] Table 2. Effects of different heat treatment temperatures and times on the electrochemical performance of the generated silicon-carbon anode materials after being made into lithium-ion batteries

[0126] As can be seen from Table 2, since the silane coupling agent contains X groups, the water and X groups in the silane coupling agent are removed as impurities as the heat treatment proceeds. However, if the heat treatment temperature is too high or the reaction time is too long, the siloxane component in the silane coupling agent will be lost, resulting in a decrease in the initial charge capacity of the lithium battery after the silicon-carbon anode material is manufactured. If the heat treatment temperature is too low or the reaction time is too short, the X groups in the silane coupling agent will remain. These residual X groups will evaporate into the porous carbon in subsequent processes, significantly adversely affecting the electrochemical performance of the resulting silicon-carbon anode material.

[0127] The data in Table 2 also show that when the heat treatment process is 400°C, the amino group in the silane coupling agent is not removed (Example 4), resulting in low initial charge capacity, sub-coulombic efficiency, and 200-cycle capacity retention of the resulting silicon-carbon negative electrode material. When the heat treatment temperature reaches 500°C for 3 hours, the amino group in the silane coupling agent can be completely removed, thereby increasing the proportion of amorphous silicon and silicon oxide compounds in the silicon-oxygen-carbon composite nanoparticles, resulting in an increase in the initial coulombic efficiency and initial charge capacity of the resulting silicon-carbon negative electrode material.

[0128] A heat treatment process at 600°C for 3 hours not only completely removes the amino groups in the silane coupling agent but also further reduces the amorphous carbon content in the silicon-oxygen-carbon composite nanoparticles. This allows the proportion of amorphous silicon and silicon oxide compounds in the silicon-oxygen-carbon composite nanoparticles to be further increased in subsequent processes, further improving the initial coulombic efficiency and initial charge capacity of the resulting silicon-carbon negative electrode material. The reduction in the amorphous carbon content in the silicon-oxygen-carbon composite nanoparticles also reduces the conductivity of the silicon-carbon negative electrode material and increases the number of pre-existing pores, resulting in a corresponding increase in the charge-discharge cycle capacity of the silicon-carbon negative electrode material.

[0129] During the heat treatment process at 1000°C for 3 hours, not only is the amino group in the silane coupling agent completely removed, but the C-C bond in the first powder is completely broken, and the Si-O and Si-C are partially broken, resulting in the loss of amorphous silicon and silicon oxides, thereby causing a decrease in the first coulombic efficiency and the first charge capacity of the silicon-carbon negative electrode material. At the same time, in the subsequent process, the number of unfilled pores in the porous carbon increases, resulting in a corresponding increase in the charge and discharge cycle capacity of the silicon-carbon negative electrode material.

[0130] It can also be seen from Table 2 that although the hydrolysis process can remove the amino group in the silane coupling agent, compared with the heat treatment process, the improvement of the electrochemical performance of the generated silicon-carbon negative electrode material is not obvious enough.

[0131] The reaction temperature of the heat treatment process is 700°C, and the reaction time is different. It can be found that when the reaction time is too short, the amorphous carbon content in the silicon-oxygen-carbon composite nanoparticles decreases in the subsequent process, and the proportion of amorphous silicon and silicon oxide compounds in the silicon-oxygen-carbon composite nanoparticles increases, resulting in an increase in the first charge capacity and the first coulomb efficiency. However, the reduction in the amorphous carbon content in the silicon-oxygen-carbon composite nanoparticles causes the conductivity of the silicon-carbon negative electrode material to deteriorate, thereby causing the charge and discharge cycle capacity of the silicon-carbon negative electrode material to deteriorate. A large amount of amorphous carbon will cause overfilling, resulting in a reduction in the volume of the unfilled portion of the pores of the porous carbon, which is not conducive to the volume expansion of the formed silicon-carbon negative electrode material during the charge and discharge cycle, thereby causing the charge and discharge cycle capacity of the silicon-carbon negative electrode material to deteriorate.

[0132] Table 3 shows the effects of varying deposition temperatures and times within the evaporation chamber in step S2 on the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery. With all other conditions remaining unchanged, adjusting only the deposition temperature and time within the deposition chamber in step S2 reveals differences in the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery.

[0133] Table 3. Effects of different deposition temperatures and deposition times on the electrochemical performance of the generated silicon-carbon anode materials after being made into lithium-ion batteries

[0134] From Table 3, it can be analyzed that the higher the deposition temperature and the longer the deposition time, the faster the decomposition rate of the first product of gasification by chemical vapor deposition reaction; and the higher the deposition temperature, the higher the temperature of evaporation in the evaporation chamber, the more mass of the first product of gasification per unit time, the more contact between the first product of gasification and porous carbon will increase, and the efficiency of depositing silicon-oxygen-carbon composite nanoparticles in the pores of porous carbon will be higher. However, if the deposition temperature is too high and the deposition time is too long, the Si and C deposited in the porous carbon will continuously react to form ceramic phase SiC. Excessive ceramic phase SiC leads to a decrease in the first charge capacity and the first coulomb efficiency of the lithium-ion battery. However, the ceramic phase SiC plays a supporting role in the electrochemical cycle of the lithium-ion battery, which is conducive to circulation. Therefore, it is necessary to control the amount of SiC generated in the ceramic phase. If the deposition temperature is too low, as in Example 8, Si-O and Si-C cannot break at the deposition temperature, resulting in the inability to generate amorphous silicon in the pores of the porous carbon, thereby making the first charge capacity and the first coulomb efficiency of the lithium-ion battery lower than Example 1.

[0135] Table 4 shows the effects of using different coating temperatures and coating times for depositing the carbon coating layer in step S3 on the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery. With all other conditions remaining unchanged, adjusting only the coating temperature and coating time for depositing the carbon coating layer in step S3 reveals differences in the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery.

[0136] Table 4. Effects of different coating temperatures and coating times on the electrochemical performance of the generated silicon-carbon negative electrode materials after being made into lithium-ion batteries

[0137] As can be analyzed from Table 4, as the coating temperature and coating time increase, the thickness of the formed carbon coating layer increases (manifested as an increase in carbon content). This increase in carbon coating layer thickness leads to a decrease in the initial charge capacity of the lithium-ion battery, an increase in the initial coulombic efficiency, and an improvement in the capacity retention rate after 200 cycles. However, if the coating temperature is too high or the coating time is too long, the amorphous silicon grains generated within the porous silicon pores will grow, resulting in a decrease in the cycling performance of the lithium-ion battery.

[0138] Table 5 shows the effects of using different acetylene flow rates for depositing the carbon coating in step S3 on the electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery. Adjusting only the acetylene flow rate for depositing the carbon coating in step S3, while keeping all other conditions constant, shows the difference in electrochemical performance of the resulting silicon-carbon anode material after fabrication into a lithium-ion battery.

[0139] Table 4. Effects of different acetylene flow rates on the electrochemical performance of the generated silicon-carbon anode material after being made into lithium-ion batteries

[0140] From Table 5, it can be analyzed that as the acetylene flow rate increases, the thickness of the formed coating layer increases (manifested as an increase in carbon content), which will lead to a decrease in the first charge capacity of the lithium-ion battery, an increase in the first coulombic efficiency, and an increase in the capacity retention rate after 200 cycles.

[0141] Table 6 shows the effects of using different silane coupling agents in step S1 on the electrochemical performance of the silicon-carbon anode material after fabrication into a lithium-ion battery. With all other conditions remaining unchanged, only the silane coupling agent in step S1 was adjusted to show the differences in electrochemical performance of the silicon-carbon anode material after fabrication into a lithium-ion battery.

[0142] Table 6. Effects of different silane coupling agents on the electrochemical performance of the generated silicon-carbon negative electrode materials after being made into lithium-ion batteries

[0143] Table 6 shows that using different silane coupling agents results in different electrochemical performance of the silicon-carbon anode materials used in lithium-ion batteries. Using silane coupling agents with longer carbon chains as the reaction raw materials results in a higher content of amorphous carbon deposited in the pores of the porous carbon. This higher amorphous carbon content improves the conductivity of the silicon-carbon anode material. However, a higher amorphous carbon content reduces the proportion of amorphous silicon formed within the pores, resulting in a decrease in the initial charge capacity of the lithium-ion battery.

[0144] Finally, it should be understood that the embodiments of the application disclosed herein are illustrations of the principles of the embodiments of the present application. Other modified embodiments are also within the scope of the present application. Therefore, the embodiments disclosed in the present application are merely examples and not limitations. Those skilled in the art can adopt alternative configurations based on the embodiments in the present application to implement the applications in the present application. Therefore, the embodiments of the present application are not limited to those embodiments that have been precisely described in the application.

Claims

1. A preparation method of a silicon-carbon anode material, characterized in that, Comprising: Remove the X group in the silane coupling agent to form a first product, and the molecular formula of the silane coupling agent is The first product is wherein n is a positive integer greater than or equal to 1, the X group includes at least one of an amino group, a chloro group, a methyl group, a methoxy group, and an ethoxy group, and the Y group includes at least one of a vinyl group, an epoxy group, a methacryloyloxy group, a mercapto group, and a ureido group; After gasifying the first product, silicon oxycarbide composite nanoparticles are formed in the pores of the porous carbon through a cracking reaction and an adsorption deposition reaction, wherein the silicon oxycarbide composite nanoparticles include silicon oxide and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide; and A carbon coating layer is deposited on the surface of the silicon oxycarbide composite nanoparticles.

2. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that, The silane coupling agent includes at least one of 3-(methacryloyloxy)propyltrimethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

3. The preparation method of the silicon-carbon anode material according to claim 1, wherein, A heat treatment process is used to remove the X group in the silane coupling agent, and the heat treatment process is carried out in an inert atmosphere and at a temperature of 500°C to 800°C.

4. The preparation method of the silicon-carbon anode material according to claim 3, wherein, Before using the heat treatment process to remove the X group in the silane coupling agent, the preparation method further includes: removing impurities in the silane coupling agent at a temperature of 100°C to 200°C.

5. The preparation method of the silicon-carbon anode material according to claim 4, characterized in that, When the X group is an amino group or a chloro group, the heat treatment process is carried out at a temperature of 500°C to 600°C; when the X group is a methyl group, the heat treatment process is carried out at a temperature of 600°C to 700°C; and when the X group is a methoxy group or an ethoxy group, the heat treatment process is carried out at a temperature of 700°C to 800°C.

6. The preparation method of the silicon-carbon anode material according to claim 1, wherein When the X group is an amino group or a chloro group, a hydrolysis process is used to remove the X group in the silane coupling agent.

7. The preparation method of the silicon-carbon anode material according to claim 1, wherein, By mass percentage, the silicon oxycarbide composite nanoparticles account for 40% to 50% of the silicon-carbon negative electrode material.

8. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that The silicon oxycarbide composite nanoparticles fill 40% to 70% of the volume of the pores.

9. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that, By mass percentage, the silicon oxycarbide composite nanoparticles include: 80% to 95% of silicon oxide, 5% to 10% of amorphous silicon, 0% to 6% of amorphous carbon, and 0% to 4% of ceramic phase silicon carbide.

10. The preparation method of the silicon-carbon anode material according to claim 1, characterized in that, The reaction temperature for forming the silicon oxycarbide composite nanoparticles in the pores of the porous carbon through a cracking reaction and an adsorption deposition reaction is 900°C to 1000°C.

11. The preparation method of the silicon-carbon anode material according to claim 1, wherein, The specific surface area of the porous carbon is 1500 to 2500 m 2 / g, and the volume of the pores is 0.6 to 1.5 g / m 3 .

12. The preparation method of the silicon-carbon anode material according to claim 11, wherein, In the pores, the volume of the micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2 nm, and the pore diameter of the mesopores is 2 nm to 50 nm.

13. The preparation method of the silicon-carbon negative electrode material according to claim 1, wherein, The process for depositing a carbon coating layer on the surface of the silicon oxycarbide composite nanoparticles includes: depositing a first carbon coating layer on the surface of the silicon oxycarbide composite nanoparticles; and then depositing a second carbon coating layer on the surface of the first carbon coating layer. The first carbon coating layer is an orderly grown amorphous carbon layer, and the second carbon coating layer has a convex and concave structure on the surface.

14. A silicon-carbon negative electrode material, characterized in that, Comprising: Porous carbon, the porous carbon includes pores, and silicon oxycarbide composite nanoparticles are formed in the pores. The silicon oxycarbide composite nanoparticles include silicon oxide and amorphous silicon, and at least one of amorphous carbon and ceramic phase silicon carbide; and the surface of the silicon oxycarbide composite nanoparticles has a carbon coating layer.

15. The silicon-carbon negative electrode material according to claim 14, wherein, The specific surface area of the porous carbon is 1500 to 2500 m 2 / g, and the volume of the pores is 0.6 to 1.5 g / m 3 .

16. The silicon-carbon negative electrode material according to claim 15, characterized in that, In the pores, the volume of the micropores accounts for more than 80% of the volume of the pores, and the rest are mesopores. The pore diameter of the micropores is less than 2 nm, and the pore diameter of the mesopores is 2 nm to 50 nm.

17. The silicon-carbon anode material according to claim 14, characterized in that, The carbon coating layer includes: a first carbon coating layer covering the surface of the silicon oxycarbide composite nanoparticles; a second carbon coating layer covering the surface of the first carbon coating layer. The first carbon coating layer is an amorphous carbon layer with ordered growth, and the second carbon coating layer has a concave-convex structure on its surface.

18. The silicon-carbon negative electrode material according to claim 14, characterized in that, The silicon oxycarbide composite nanoparticles fill 40% to 70% of the volume of the pores.

19. The silicon-carbon negative electrode material according to claim 14, wherein By mass percentage, the silicon oxycarbide composite nanoparticles include: 80% to 95% of silicon oxide compounds, 5% to 10% of amorphous silicon, 0% to 6% of amorphous carbon, and 0% to 4% of ceramic phase silicon carbide.

20. A lithium-ion battery, characterized in that, It includes a negative electrode, and the negative electrode includes the silicon-carbon negative electrode material according to any one of claims 14 to 19.

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