Silicon-carbon composite material, method for preparing the same, and use thereof

Abstract

The application relates to the field of lithium ion battery negative electrode material preparation, and discloses a silicon-carbon composite material and a preparation method and application thereof. The composite material comprises graphite, nano-silicon, a nitrogen-containing carbon layer between the graphite and the nano-silicon, and a carbon coating layer wrapping the nano-silicon. The silicon-carbon composite material provided by the application has good charge-discharge cycle stability when applied to a lithium battery negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material preparation, specifically to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] In recent years, the new energy industry has ushered in unprecedented development opportunities. Among them, lithium-ion batteries, as the most promising key product to replace traditional fossil fuels, have been widely used in various fields such as electronic products, electric vehicles, and energy storage. Compared with the currently widely used graphite anode, silicon-based materials have higher capacity and are expected to meet the ever-increasing energy density requirements of lithium batteries; however, silicon-based materials have low conductivity, and silicon experiences severe volume expansion during lithium insertion / extraction.

[0003] Typically, nano-sized silicon particles are used in combination with graphite-based anode materials to simultaneously address the issues of volume expansion and poor conductivity of silicon during lithium insertion / extraction. However, due to their high surface energy, nano-silicon particles tend to agglomerate during dispersion. This makes it difficult to uniformly distribute the nano-silicon material in silicon-carbon anode materials formed by combining them with graphite-based anode materials. This results in uneven lithiation and excessive localized volume expansion after lithium insertion, significantly impacting the capacity of the anode material. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in current silicon-carbon composite materials and to provide a silicon-carbon composite material, its preparation method, and its applications. The silicon-carbon composite material provided by this invention exhibits good charge-discharge cycle stability when used as a negative electrode material in lithium batteries.

[0005] To achieve the above objectives, the first aspect of the present invention provides a silicon-carbon composite material, the composite material comprising graphite, nano-silicon, a nitrogen-containing carbon layer between the graphite and the nano-silicon, and a carbon coating layer encapsulating the nano-silicon.

[0006] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0007] (1) In the presence of a solvent, a grafting agent, a coating agent, graphite and nano-silicon are mixed to obtain a dispersion; the dispersion is subjected to a hydrothermal reaction to obtain a silicon-carbon precursor;

[0008] (2) The silicon carbide precursor is subjected to carbonization treatment;

[0009] The grafting agent is selected from aniline and C6-C. 11 At least one of the aniline derivatives.

[0010] The third aspect of this invention provides the application of the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect in the negative electrode of a lithium-ion battery.

[0011] The beneficial effects of the present invention through the above technical solution include:

[0012] The silicon-carbon composite material provided by this invention enables uniform dispersion and dense coating of nano-silicon on the graphite surface, enhancing the synergistic effect between nano-silicon and graphite. Furthermore, the carbon coating layer encapsulating the nano-silicon effectively isolates the nano-silicon particles, preventing self-aggregation and mitigating volume expansion during charge-discharge processes. When applied to lithium-ion batteries, the silicon-carbon composite material exhibits excellent charge-discharge cycle stability.

[0013] The silicon-carbon composite material preparation method provided by this invention achieves control over the bonding force between graphite and nano-silicon, as well as the surface coating of nano-silicon, through a one-step hydrothermal method. This results in the uniform distribution of nano-silicon on the graphite surface and simultaneous carbon coating of the nano-silicon surface, avoiding the self-aggregation problem of nano-silicon on the graphite surface. The silicon-carbon composite material preparation method provided by this invention is simple and efficient. Attached Figure Description

[0014] Figure 1 This is a SEM image of the silicon-carbon composite material prepared in Example 1;

[0015] Figure 2 This is a TEM image of the silicon-carbon composite material prepared in Example 1;

[0016] Figure 3 This is a pore distribution diagram of the silicon-carbon composite materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0017] Figure 4 These are the cycle stability test curves of the silicon-carbon composite materials prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The first aspect of the present invention provides a silicon-carbon composite material, the composite material comprising graphite, nano-silicon, a nitrogen-containing carbon layer between the graphite and the nano-silicon, and a carbon coating layer encapsulating the nano-silicon.

[0020] The composition of the composite material described in this invention was obtained through a combination of TEM and EDS tests. Specifically, TEM can be used to observe the carbon layer between graphite and nano-silicon, as well as the carbon coating layer on the surface of nano-silicon. EDS can be used to measure the distribution of different elements. The combination of the two tests can prove that a composite material with the above-mentioned structure is obtained.

[0021] The present invention allows for a wide range of selection for the content of nano-silicon. Preferably, in the silicon-carbon composite material, the mass content of nano-silicon is 40-80% based on the total mass of the silicon-carbon composite material. Specifically, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of these values, preferably 45-70%.

[0022] The nano-silicon content in the silicon-carbon composite material described in this invention was determined by thermogravimetric analysis, specifically using an SDT Q600 thermal comprehensive analysis instrument from TA Instruments, USA. Test conditions: test range 25℃-800℃, gas flow rate 100ml / min, heating rate 10℃ / min.

[0023] The present invention allows for a wide range of selection for the graphite content in the composite material. Preferably, the mass ratio of graphite to nano-silicon is 0.2-1.5:1, specifically 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, and any two of these values ​​forming a range, preferably 0.25-1:1.

[0024] The graphite content in the composite material of the present invention is obtained by calculation based on the amount of material fed.

[0025] According to the present invention, preferably, the nitrogen content is 0.5-2% by mass, based on the total weight of the silicon-carbon composite material, specifically 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, and any range of any two of these values. This preferred embodiment is beneficial for improving the bonding stability between graphite and silicon materials, thereby improving cycle performance; it also helps to improve the electrical conductivity of the carbon materials.

[0026] The nitrogen content in the silicon-carbon composite material described in this invention was determined by X-ray photoelectron spectroscopy (XPS), specifically using an ESCALAB 250Xi X-ray photoelectron spectroscopy instrument from Thermo Fisher Scientific, USA. Test conditions: room temperature 25℃, vacuum degree less than 5×10⁻¹⁰ mba, operating voltage 15 kV, using Al Kα as the X-ray source.

[0027] According to the present invention, preferably, the thickness of the nitrogen-containing carbon layer is 1-5 nm, specifically 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, and any range of any two of these values. Controlling the thickness of the nitrogen-containing carbon layer within the above-mentioned preferred range is more conducive to improving cycle performance; it also helps to improve the electrical conductivity of carbon materials.

[0028] The thickness of the carbon coating layer described in this invention was measured by TEM.

[0029] According to the present invention, preferably, the thickness of the carbon coating layer is 2-10 nm, specifically 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, and any two of these values ​​forming a range. Controlling the thickness of the carbon coating layer within the above-mentioned preferred range is beneficial for providing good electron and lithium ion transport channels, improving the conductivity of silicon materials and the lithium ion diffusion rate, and can also alleviate the volume expansion of silicon during charging and discharging, prevent silicon particle breakage, and improve the stability of the material.

[0030] The thickness of the carbon coating layer described in this invention was measured by TEM.

[0031] According to the present invention, preferably, the carbon content in the silicon-carbon composite material is 20-60% by mass, more preferably 30-55%, based on the total mass of the silicon-carbon composite material.

[0032] It is understandable that the carbon element here refers to all carbon elements in the composite material, including graphite and amorphous carbon.

[0033] The carbon content in the silicon-carbon composite material described in this invention was determined by X-ray photoelectron spectroscopy (XPS), specifically using an ESCALAB 250Xi X-ray photoelectron spectroscopy instrument from Thermo Fisher Scientific, USA. Test conditions: room temperature 25℃, vacuum degree less than 5×10⁻¹⁰ mba, operating voltage 15 kV, using Al Kα as the X-ray source.

[0034] According to the present invention, preferably, the pore size of the silicon-carbon composite material is in the range of 2-50 nm, more preferably in the range of 2-10 nm. This preferred embodiment provides greater structural stability within this pore size range, making it less likely to create spatial barriers for lithium ions. The framework structure can effectively buffer the volume expansion of silicon, which is beneficial to improving the cycling stability of the material.

[0035] According to the present invention, preferably, the pore volume of the silicon-carbon composite material is 0.03-0.15 cm³. 3 / g, specifically 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.1cm 3 / g, 0.11cm 3 / g, 0.12cm 3 / g, 0.13cm 3 / g, 0.14cm 3 / g, 0.15cm 3 / g, and the range of any two points among these values, preferably 0.05-0.09cm. 3 / g. This preferred embodiment facilitates the penetration of the electrolyte into the material, enhances the material's adsorption capacity for the electrolyte, promotes lithium ion transport, and improves the material's specific capacity and cycle stability.

[0036] The pore distribution of the silicon-carbon composite material described in this invention was measured using BET.

[0037] According to the present invention, preferably, the median particle size of the nano-silicon is 30-200 nm, more preferably 50-100 nm. Nano-silicon materials of this size can effectively reduce the transport distance of electrons and ions, and are easy to coat and graft.

[0038] The median particle size of the nano-silicon described in this invention was determined by dynamic light scattering characterization.

[0039] The nano-silicon described in this invention can be obtained commercially or prepared in-house using conventional methods in the field (such as the sanding method), and has the advantages of controllable cost and stable performance.

[0040] This invention does not impose a particular limitation on the median particle size of the silicon-carbon composite material, which can be appropriately selected according to different application scenarios. Preferably, the median particle size of the silicon-carbon anode material is 10-25 μm.

[0041] The median particle size of the silicon-carbon composite material described in this invention was measured using a Malvern laser particle size analyzer.

[0042] According to a preferred embodiment of the present invention, a silicon-carbon composite material is provided, the composite material comprising graphite, nano-silicon, amorphous carbon, and nitrogen.

[0043] Preferably, in the silicon-carbon composite material, the mass content of nano-silicon is 40-80%, more preferably 45-70%, based on the total mass of the silicon-carbon composite material;

[0044] Preferably, the mass ratio of graphite to nano-silicon is 0.2-1.5:1, more preferably 0.25-1:1;

[0045] Preferably, the nitrogen content is 0.5-2% by mass, based on the total weight of the silicon-carbon composite material;

[0046] Preferably, in the silicon-carbon composite material, the mass content of carbon element is 20-60%, more preferably 30-55%, based on the total mass of the silicon-carbon composite material.

[0047] This invention does not impose any particular limitation on the preparation method of the silicon-carbon composite material, as long as a silicon-carbon composite material with the above-mentioned characteristics can be obtained. To further improve the performance of the silicon-carbon composite material, and also to better illustrate the preparation of the silicon-carbon composite material, this invention also provides a method for preparing the silicon-carbon composite material.

[0048] A second aspect of the present invention provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0049] (1) In the presence of a solvent, a grafting agent, a coating agent, graphite and nano-silicon are mixed to obtain a dispersion; the dispersion is subjected to a hydrothermal reaction to obtain a silicon-carbon precursor;

[0050] (2) The silicon carbide precursor is subjected to carbonization treatment;

[0051] The grafting agent is selected from aniline and C6-C. 11 At least one of the aniline derivatives.

[0052] The method for preparing silicon-carbon anode material provided by this invention employs the synergistic effect of grafting agent and coating agent, achieving self-assembly of grafting agent and coating agent under hydrothermal reaction conditions. The coated nano-silicon is uniformly adsorbed on the graphite surface, and the interaction between nano-silicon and graphite is enhanced. Subsequent carbonization yields the silicon-carbon composite material described in the first aspect, which has significantly improved conductivity and stability in lithium battery anode material applications.

[0053] The present invention does not particularly limit the type of graphite used; it can be artificial graphite or natural graphite. For example, it can be spherical graphite.

[0054] The grafting agent used in this invention can connect one end to the graphite surface and the other end to nano-silicon, thereby grafting nano-silicon onto the graphite surface. According to this invention, the grafting agent is selected from aniline and C6-C... 11 At least one of the aniline derivatives, preferably selected from at least one of o-ethylaniline, m-methylaniline, p-butylaniline, p-phenylenediamine, p-ethoxyaniline, and 3-methoxyaniline. This preferred embodiment is beneficial for improving the cycling performance of the material and also for improving the electrical conductivity of the carbon material.

[0055] The coating agent used in this invention can coat the surface of nano-silicon, preventing the re-agglomeration of the nano-silicon. According to this invention, preferably, the coating agent is selected from at least one of polyvinyl alcohol, ethyl cellulose, polyvinyl butyral, polyvinylpyrrolidone, and phenolic resin.

[0056] The present invention allows for a wide range of solvent selection. Preferably, the solvent is selected from at least one of ethanol, methanol, water, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0057] According to the present invention, preferably, the median particle size of the nano-silicon is 30-200 nm, more preferably 50-100 nm.

[0058] According to the present invention, preferably, the mass ratio of graphite to nano-silicon is 0.2-1.5:1, more preferably 0.25-1:1.

[0059] According to the present invention, preferably, the mass ratio of the coating agent to nano-silicon is 0.05-0.4:1, more preferably 0.1-0.3:1. This preferred embodiment facilitates control of the thickness of the obtained carbon coating layer within the preferred range described in the first aspect.

[0060] According to the present invention, preferably, the mass ratio of grafting agent to nano-silicon is 0.01-0.1:1, more preferably 0.03-0.08:1. This preferred embodiment facilitates the application of the grafting agent and controls the uniform distribution of nano-silicon on the graphite surface.

[0061] The present invention does not impose a particular limitation on the amount of solvent used, as long as the other components are mixed evenly, and can be appropriately selected according to the actual situation.

[0062] The present invention does not impose any particular limitation on the order in which the solvent, grafting agent, coating agent, graphite, and nano-silicon are added during the mixing process described in step (1). They can be added separately or together. In order to achieve uniform mixing, the embodiments of the present invention preferably adopt the method of adding the solvent and coating agent first, and then adding the nano-silicon, graphite, and grafting agent.

[0063] In this invention, the self-assembly of the grafting agent and the coating agent can be achieved under hydrothermal reaction conditions, so that the coated nano-silicon is uniformly adsorbed on the graphite surface, and the nano-silicon material is uniformly dispersed on the graphite surface. Preferably, the hydrothermal reaction conditions in step (1) include: a temperature of 120-220℃, preferably 150-200℃; and a time of 20-150 min, preferably 30-120 min.

[0064] According to the present invention, preferably, the carbonization conditions in step (2) include: a temperature of 500-800°C and a time of 1-8 hours.

[0065] According to the present invention, preferably, the carbonization process is carried out in an inert atmosphere.

[0066] The present invention allows for a wide range of choices for the types of inert gases, including conventional choices in the field. Examples include nitrogen, argon, helium, and neon.

[0067] The third aspect of this invention provides the application of the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect in the negative electrode of a lithium-ion battery.

[0068] The silicon-carbon composite material provided by this invention, when applied to the negative electrode of a lithium-ion battery, exhibits excellent charge-discharge cycle stability.

[0069] According to a preferred embodiment of the present invention, a lithium-ion battery includes a positive electrode material, a negative electrode material, an electrolyte, and a separator, wherein the negative electrode material is the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0070] The present invention will be described in detail below through embodiments.

[0071] In the following embodiments, scanning electron microscopy (SEM) was used to characterize the morphology of the composite material. Specifically, the instrument used was a ZEISS-MERLIN high-resolution field emission scanning electron microscope from Germany. The test conditions were as follows: the sample was directly pressed onto the sample stage containing conductive tape, and then inserted into the electron microscope for observation; the accelerating voltage was 3kV.

[0072] In this invention, the morphology of the composite material was further characterized using a FEI-Tecnai transmission electron microscope (TEM). Test conditions: The sample was placed on a copper support mesh and then inserted into the electron microscope for observation.

[0073] In this invention, the median particle size of the composite material was obtained by dynamic light scattering characterization using a Malvern Panalytical MS-3000 laser particle size analyzer. Test conditions: The sample was dispersed in deionized water at a concentration of 0.01 mg / ml, and tested after sonication for 10 minutes. The instrument's light-blocking setting was set between 5% and 20%.

[0074] In this invention, the silicon content of the composite material was determined using an SDT Q600 thermal comprehensive analysis instrument from TA Instruments, USA. Test conditions: test range 25℃-800℃, gas flow rate 100ml / min, heating rate 10℃ / min;

[0075] In this invention, the carbon and nitrogen elements of the composite material were measured using an ESCALAB 250Xi X-ray photoelectron spectroscopy system from Thermo Fisher Scientific, USA. The testing conditions were: room temperature 25℃, vacuum degree less than 5×10⁻¹⁰ mba, operating voltage 15 kV, and Al Kα as the X-ray source.

[0076] Example 1

[0077] Weigh 80 ml of anhydrous ethanol, add 3 g of ethyl cellulose, stir until completely dissolved, then add 20 g of nano-silicon (median particle size 80 nm), 16 g of graphite, and 1 g of p-phenylenediamine sequentially. After stirring evenly, transfer to a stainless steel-lined polytetrafluoroethylene reactor and treat at 150 °C for 90 min. Then, after filtration, washing, and drying, obtain a silicon-carbon anode precursor. Carbonize the silicon-carbon anode precursor in a high-temperature tube furnace at 800 °C for 2 h to obtain the silicon-carbon anode material.

[0078] An exemplary SEM image of the silicon-carbon composite material prepared in Example 1 is provided, such as... Figure 1 As shown. From Figure 1 As can be seen, the material surface is uniformly coated with a carbon coating layer, the overall morphology of the material is uniform, and the sphericity is high.

[0079] An TEM image of the silicon-carbon composite material prepared in Example 1 is provided as an example. Figure 2 As shown. From Figure 2 As can be seen, there is a nitrogen-containing carbon layer between graphite and nano-silicon, and there is a carbon coating layer on the outer surface of nano-silicon.

[0080] An exemplary pore size distribution diagram of the silicon-carbon composite material prepared in Example 1 is provided, as follows: Figure 3 As shown. From Figure 3 As can be seen, the pore size of Example 1 is mainly a single mesopore of 2-5 nm, indicating that the stacking form of nano-silicon and graphite in the material has a single orientation.

[0081] Example 2

[0082] Weigh 80 ml of N-methylpyrrolidone, add 4 g of polyvinylpyrrolidone, stir until completely dissolved, then add 20 g of nano-silicon (median particle size 50 nm), 20 g of graphite powder, and 1.6 g of p-ethoxyaniline sequentially. After stirring evenly, transfer to a stainless steel-lined polytetrafluoroethylene reactor and treat at 200 °C for 120 min. Then, after filtration, washing, and drying, obtain a silicon-carbon anode precursor. Carbonize the silicon-carbon anode precursor in a high-temperature tube furnace at 650 °C for 5 h to obtain the silicon-carbon anode material.

[0083] Example 3

[0084] Weigh 80 ml of N,N-dimethylformamide, add 2.5 g of phenolic resin, stir until completely dissolved, then add 20 g of nano-silicon (median particle size 100 nm), 10 g of graphite powder, and 0.8 g of o-ethylaniline sequentially. After stirring evenly, transfer to a stainless steel-lined polytetrafluoroethylene reactor and treat at 180 °C for 30 min. Then, after filtration, washing, and drying, obtain a silicon-carbon anode precursor. Carbonize the silicon-carbon anode precursor in a high-temperature tube furnace at 700 °C for 3 h to obtain the silicon-carbon anode material.

[0085] Example 4

[0086] The method of Example 1 was followed, except that the amount of p-phenylenediamine added was 0.2 g, and a silicon-carbon composite material was obtained. Its composition and characteristic parameters are shown in Table 1.

[0087] Example 5

[0088] The method of Example 1 was followed, except that 1g of ethyl cellulose was added to obtain a silicon-carbon composite material, the composition and characteristic parameters of which are shown in Table 1.

[0089] Comparative Example 1

[0090] The procedure was carried out according to Example 1, except that the grafting agent p-phenylenediamine was not added, resulting in a silicon-carbon composite material, the composition of which and its characteristic parameters are shown in Table 1.

[0091] Figure 3 This is a pore size distribution diagram of the silicon-carbon composite material in Comparative Example 1. Figure 3As can be seen from the data, in Comparative Example 1, no grafting agent was added, and the pore size of the material was mainly mesopores between 2-50 nm and macropores exceeding 50 nm. This indicates that without the addition of grafting agent, the nano-silicon exhibits a multi-level porous structure on the graphite surface due to stacking.

[0092] Comparative Example 2

[0093] The method of Example 1 was followed, except that the coating agent ethyl cellulose was not added, resulting in a silicon-carbon composite material, the composition of which and its characteristic parameters are shown in Table 1.

[0094] Figure 3 The figure shows the pore size distribution of the silicon-carbon composite material prepared in Comparative Example 2. As can be seen from the figure, no coating agent was added in Comparative Example 2. The material has a small number of mesopores between 2-5 nm. The material has a dense structure, which is not conducive to the wetting of the electrolyte, affects the transfer of lithium ions between silicon and graphite, and affects the performance of the material's electrical properties.

[0095] Table 1

[0096]

[0097]

[0098] Test case

[0099] In this invention, the LAND battery testing system is used to test the electrochemical performance. The testing method includes: uniformly coating a negative electrode material, conductive carbon black, and binder onto a copper foil in an 8:1:1 ratio to form an electrode sheet with an areal density of 50-100 mg / cm³. 2 The test temperature was 25℃. Composite materials and lithium metal sheets from each example and comparative example were used as the positive and negative electrodes, respectively. A 1 mol / L LiPF6 solution was used as the electrolyte, and a polypropylene microporous membrane was used as the separator. CR2016 button cells were assembled. First discharge cycle: rate of 0.05C, voltage range 0.005V-1.5V, temperature 25℃. Cyclic charge / discharge cycle: rate of 0.2C, voltage range 0.005V-1.5V, temperature 25℃. Ten button cells were assembled for each sample, and battery performance was tested under the same voltage and current, with the average value taken. Battery performance is shown in Table 2.

[0100] Table 2

[0101]

[0102] As can be seen from the results in Table 2, the lithium-ion battery made using the composite material provided by this invention has better cycle performance.

[0103] pass Figure 4These are the cycle stability test curves of batteries made from silicon-carbon composite materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 under a charge-discharge current of 0.2C. From... Figure 4 As can be seen, compared with Comparative Example 1 and Comparative Example 2, the lithium-ion battery made using the composite material provided in Example 1 of the present invention has better cycle performance.

[0104] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The composite material includes graphite, nano-silicon, a nitrogen-containing carbon layer between the graphite and the nano-silicon, and a carbon coating layer that encapsulates the nano-silicon.

2. The composite material according to claim 1, wherein, In the silicon-carbon composite material, based on the total mass of the silicon-carbon composite material, the mass content of nano-silicon is 40-80%, preferably 45-70%; Preferably, the mass ratio of graphite to nano-silicon is 0.2-1.5:1, more preferably 0.25-1:1; Preferably, the nitrogen content is 0.5-2% by mass, based on the total weight of the silicon-carbon composite material; Preferably, the thickness of the nitrogen-containing carbon layer is 1-5 nm.

3. The composite material according to claim 1 or 2, wherein, The thickness of the carbon coating layer is 2-10 nm; Preferably, in the silicon-carbon composite material, the mass content of carbon element is 20-60%, more preferably 30-55%, based on the total mass of the silicon-carbon composite material.

4. The composite material according to any one of claims 1-3, wherein, The pore size of the silicon-carbon composite material is in the range of 2-50 nm, preferably in the range of 2-10 nm; Preferably, the pore volume of the silicon-carbon composite material is 0.03-0.15 cm³. 3 / g, preferably 0.05-0.09cm 3 / g; Preferably, the median particle size of the silicon-carbon composite material is 10-25 μm; Preferably, the median particle size of the nano-silicon is 30-200 nm, and more preferably 50-100 nm.

5. A method for preparing a silicon-carbon composite material, characterized in that, The method includes the following steps: (1) In the presence of a solvent, a grafting agent, a coating agent, graphite and nano-silicon are mixed to obtain a dispersion; the dispersion is subjected to a hydrothermal reaction to obtain a silicon-carbon precursor; (2) The silicon carbide precursor is subjected to carbonization treatment; The grafting agent is selected from aniline and C6-C. 11 At least one of the aniline derivatives.

6. The method according to claim 5, wherein, The grafting agent is selected from at least one of o-ethylaniline, m-methylaniline, p-butylaniline, p-phenylenediamine, p-ethoxyaniline, and 3-methoxyaniline; Preferably, the coating agent is selected from at least one of polyvinyl alcohol, ethyl cellulose, polyvinyl butyral, polyvinylpyrrolidone, and phenolic resin.

7. The method according to claim 5 or 6, wherein, The median particle size of the nano-silicon is 30-200 nm, preferably 50-100 nm; Preferably, the mass ratio of graphite to nano-silicon is 0.2-1.5:1, more preferably 0.25-1:1; Preferably, the mass ratio of the coating agent to nano-silicon is 0.05-0.4:1, more preferably 0.1-0.3:1; Preferably, the mass ratio of grafting agent to nano-silicon is 0.01-0.1:1, more preferably 0.03-0.08:

1.

8. The method according to any one of claims 5-7, wherein, The conditions for the hydrothermal reaction in step (1) include: a temperature of 120-220℃, preferably 150-200℃; and a time of 20-150 min, preferably 30-120 min.

9. The method according to any one of claims 5-8, wherein, The carbonization conditions in step (2) include: a temperature of 500-800℃ and a time of 1-8h; Preferably, the carbonization process is carried out in an inert atmosphere.

10. The application of a silicon-carbon composite material according to any one of claims 1-4 or a silicon-carbon composite material prepared by any one of claims 5-9 in a lithium-ion battery anode.

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