Silicon-carbon composite material, and preparation method therefor and use thereof

Abstract

A silicon-carbon composite material, and a preparation method therefor and a use thereof. The silicon-carbon composite material comprises a silicon-carbon composite particle; and the silicon-carbon composite particle comprises a carbon matrix and carbon nanotubes distributed in the carbon matrix, the tubes of the carbon nanotubes containing silicon nanowires.

Description

Silicon-carbon composite material, preparation method and application thereof

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202410870540.9, filed on June 08, 2024, and entitled "Silicon-carbon composite material, preparation method and application thereof", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to lithium ion battery materials, in particular, to a silicon-carbon composite material, a preparation method and application thereof. BACKGROUND

[0004] In the related art, most of the negative electrode materials of power batteries use graphite materials, which are difficult to meet market demand. As a new negative electrode material, silicon material has become the most potential negative electrode material because of its high theoretical capacity, low lithium intercalation platform, and abundant resources. However, silicon material will have a large-scale volume expansion during lithium intercalation, which will cause the structure of silicon material to be pulverized and the stability of the solid electrolyte interface (SEI) to be unstable, ultimately leading to a decrease in lithium intercalation capacity. In order to alleviate the lithium intercalation size effect of silicon material, the silicon material is usually nano-sized and amorphous, which reduces the size of the silicon material and alleviates the lithium intercalation expansion stress. However, the smaller size of amorphous nano-silicon has the disadvantages of high surface area and strong surface activity, which leads to easy aggregation and oxidation of the amorphous nano-silicon, and further leads to a decrease in the capacity of the negative electrode, a decrease in the initial efficiency, and a high expansion rate. SUMMARY

[0005] The purpose of the present disclosure is to provide a silicon-carbon composite material, a preparation method and application thereof. The silicon-carbon composite material has a low expansion rate and good stability, and when used as a negative electrode material of a lithium ion battery, a lower expansion rate and better electrochemical performance can be obtained.

[0006] To achieve the above purpose, the first aspect of the present disclosure provides a silicon-carbon composite material, the silicon-carbon composite material comprising silicon-carbon composite particles.

[0007] The silicon-carbon composite particles comprise a carbon matrix and carbon nanotubes distributed in the carbon matrix, and the carbon nanotubes contain silicon nanowires in the tubes.

[0008] Optionally, the silicon nanowires comprise amorphous silicon.

[0009] Optionally, the average diameter of the silicon nanowires is 3-60 nm, and / or

[0010] The average length of the silicon nanowires is 3-26 μm.

[0011] Optionally, the carbon nanotubes comprise single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0012] Optionally, the silicon-carbon composite material satisfies at least one of the following:

[0013] a. the average diameter of the carbon nanotubes is 10-100 nm;

[0014] b. the average length of the carbon nanotubes is 5-30 pm;

[0015] c. the aspect ratio of the carbon nanotubes is 50-3000.

[0016] Optionally, the multi-walled carbon nanotubes comprise 2-10 tube walls, and at least part of the adjacent tube walls are distributed with amorphous nanosilicon, the amorphous nanosilicon comprising silicon nanowires and / or nanosilicon particles.

[0017] Optionally, the ratio of the total volume of the silicon nanowires to the total volume of the intratubular space of the carbon nanotubes is 0.2-0.8.

[0018] Optionally, the outer walls of the carbon nanotubes and / or the carbon matrix are distributed with amorphous nanosilicon, the amorphous nanosilicon comprising silicon nanowires and / or nanosilicon particles.

[0019] Optionally, the silicon-carbon composite particle further comprises a carbon coating layer;

[0020] Optionally, the thickness of the carbon coating layer is 5-25 nm.

[0021] Optionally, the silicon-carbon composite material satisfies at least one of the following:

[0022] A. the D50 particle size of the silicon-carbon composite material is 6-20 pm;

[0023] B. the specific surface area of the silicon-carbon composite material is 0.3-3.0 m 2 / g;

[0024] C. the powder conductivity of the silicon-carbon composite material is (1-10) x 10 5 S / m;

[0025] D. the silicon-carbon composite particle is spherical and / or spheroidal.

[0026] Optionally, the content of carbon element in the silicon-carbon composite material is 50-80 w.t.%.

[0027] Optionally, the silicon-carbon composite material contains a pre-lithiation material.

[0028] Optionally, the carbon matrix comprises amorphous carbon and / or graphite.

[0029] The second aspect of the present disclosure provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0030] S1, depositing silicon atoms on graphene, converting the graphene into carbon nanotubes, and then forming silicon nanowires in the carbon nanotubes to obtain a carbon nanotube-silicon nanowire composite material;

[0031] S2, mixing and granulating the carbon nanotube-silicon nanowire composite material and a carbon source to obtain a silicon-carbon composite material.

[0032] Optionally, step S1 comprises the following steps:

[0033] S11, cracking a first silane gas to deposit the silicon atoms on the graphene;

[0034] S12, curling the graphene under the action of a catalyst and heating to convert the graphene into the carbon nanotubes, and depositing the silicon atoms on the inner wall of the carbon nanotubes.

[0035] Optionally, step S1 further comprises the following step:

[0036] S13, introducing a second silane gas into the carbon nanotubes obtained in step S12, and cracking the second silane gas to form silicon nanowires from the silicon atoms deposited on the inner wall.

[0037] Optionally, in steps S11 and / or S12, the first silane gas drives the graphene into a fluidized state.

[0038] Optionally, steps S11, S12 and S13 are carried out in a fluidized bed.

[0039] Optionally, in step S11, the reaction temperature is 500-600℃ and the time is 60-210 min.

[0040] Optionally, the flow rate of the first silane gas is 1.2-5.6 sccm per 1 g of the graphene.

[0041] Optionally, in step S12, the catalyst comprises one or more of elemental Pd, elemental Cu, elemental Co and elemental Ni.

[0042] In step S12, the heating time is 200-500 min and the heating temperature is 400-460℃.

[0043] The specific surface area of the carbon nanotubes is 50-150 m 2 / g.

[0044] Optionally, in step S13, the reaction temperature is 420-440℃, and the time is 10-30h.

[0045] The flow rate of the second silane gas is 3.6-8.5sccm relative to 1g of the graphene.

[0046] Optionally, in step S2, the mixing granulation method comprises spray drying granulation.

[0047] Optionally, the spray drying granulation conditions satisfy: the spray outlet temperature is 60-250℃, and the time is 10-60min.

[0048] Optionally, the carbon source comprises one or more of pitch, graphene, hard carbon, graphite and carbon nanotube.

[0049] Optionally, the amount of the carbon source is 40-50w.t.% in terms of carbon element relative to the total weight of the carbon nanotube-silicon nanowire composite and the carbon source.

[0050] Optionally, the method further comprises carbon coating on the granules obtained by the mixing granulation.

[0051] Optionally, the carbon coating method comprises pitch carbonization or chemical vapor deposition coating.

[0052] The third aspect of the present disclosure provides a negative electrode comprising the silicon-carbon composite material of the first aspect of the present disclosure or the silicon-carbon composite material prepared by the method of the second aspect of the present disclosure.

[0053] The fourth aspect of the present disclosure provides a lithium ion battery comprising the negative electrode of the third aspect of the present disclosure.

[0054] Through the above technical solution, the method of the present disclosure first cracks the silane gas into silicon atoms, then rolls the graphene to form carbon nanotubes, obtains carbon nanotubes with silicon atoms deposited on the inner wall, and connects the silicon atoms to form silicon nanowires in the subsequent step to obtain a carbon nanotube-silicon nanowire composite. Then the carbon nanotube-silicon nanowire composite is mixed with the carbon source for granulation, so that it is dispersed in the carbon matrix. The method of the present disclosure can prepare a silicon-carbon composite material with a specific structure through simple operation steps, and is easy to industrialize.

[0055] The silicon-carbon composite material of the present disclosure has a carbon matrix and carbon nanotubes dispersed in the carbon matrix, and the carbon nanotubes contain silicon nanowires. In one aspect, the nanosilicon in the form of nanowires has a low specific surface area, and placing the silicon nanowires in the carbon nanotubes can reduce the oxidation activity of the silicon nanowires and make it less likely to undergo side reactions, thus solving the problem of easy reaction of the silicon surface. Compared with the silicon-carbon negative electrode material in the related art which uses nanosilicon with a high surface area and strong surface activity, the silicon-carbon composite material of the present disclosure used as a lithium ion battery negative electrode material can avoid the reduction of the initial efficiency and capacity of the battery, and can obtain uniform capacity and swelling stress, thus avoiding the problems of high local capacity and large local swelling stress of the lithium-embedded particles. In another aspect, the carbon matrix can avoid the agglomeration of the nanosilicon and the carbon nanotubes, and reduce the expansion rate of the silicon-carbon composite material. The silicon-carbon composite material of the present disclosure has the characteristics of structural stability and high electrical conductivity, and when used as a lithium ion battery negative electrode material, it can obtain a low expansion rate and good electrochemical performance.

[0056] Other features and advantages of the present disclosure will be described in detail in the following detailed description section. BRIEF DESCRIPTION OF DRAWINGS

[0057] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, and are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation of the present disclosure. In the drawings:

[0058] FIG. 1 is an SEM image of the silicon-carbon composite material A1 prepared in Example 1 of the present disclosure.

[0059] FIG. 2 is an XRD image of the silicon-carbon composite material A1 prepared in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0060] The detailed description of the present disclosure is described below in conjunction with the accompanying drawings. It should be understood that the detailed description described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0061] The first aspect of the present disclosure provides a silicon-carbon composite material, which comprises silicon-carbon composite particles.

[0062] The silicon-carbon composite particles comprise a carbon matrix and carbon nanotubes distributed in the carbon matrix, and the carbon nanotubes contain silicon nanowires in the tubes.

[0063] The silicon-carbon composite material of the present disclosure has a carbon matrix and carbon nanotubes dispersed in the carbon matrix, and the carbon nanotubes contain silicon nanowires. The carbon nanotubes contain nanosilicon, which exists in the form of silicon nanowires, which can reduce the specific surface area and oxidation activity of the nanosilicon. When the silicon-carbon composite material of the present disclosure is used as a negative electrode material for a lithium ion battery, on the one hand, the initial efficiency and capacity of the battery can be avoided, and on the other hand, a relatively uniform battery capacity and expansion stress can be obtained, and the problem of local high lithium intercalation capacity and local high expansion stress of the particles can be avoided. In addition, the carbon nanotubes can avoid the agglomeration of the nanosilicon, and the carbon matrix can avoid the agglomeration of the carbon nanotubes, thereby reducing the expansion rate of the silicon-carbon composite material. The silicon-carbon composite material of the present disclosure has the characteristics of structural stability and high electrical conductivity, and when it is used as a negative electrode material for a lithium ion battery, a lower expansion rate and better electrochemical performance can be obtained.

[0064] In the present disclosure, the carbon nanotubes are distributed in the carbon matrix, which can be understood as a mixed state of the carbon nanotubes and the carbon matrix. The carbon nanotubes can be distributed in the carbon matrix, or a part of the carbon nanotubes can be distributed in the carbon matrix, and the other part of the carbon nanotubes can be located on the surface of the carbon matrix.

[0065] In the present disclosure, the carbon matrix includes but is not limited to amorphous carbon, graphite, etc.

[0066] In order to obtain better electrochemical performance, according to an embodiment of the present disclosure, the silicon nanowires include amorphous silicon.

[0067] According to an embodiment of the present disclosure, the average diameter of the silicon nanowires is 3-60 nm, preferably 15-35 nm, including but not limited to 3 nm, 10 nm, 15 nm, 22 nm, 28 nm, 30 nm, 35 nm, 42 nm, 46 nm, 50 nm, 55 nm, 60 nm, or a range consisting of any two of them; and / or, the average length of the silicon nanowires is 3-26 μm, preferably 15-25 μm, including but not limited to 3 μm, 5 μm, 8 μm, 12 μm, 15 μm, 20 μm, 23 μm, 26 μm, or a range consisting of any two of them; the diameters and lengths of all the silicon nanowires can be the same or different. In the same carbon nanotube, the maximum diameter of the silicon nanowires is smaller than the diameter of the carbon nanotube, and the maximum length is not greater than the length of the carbon nanotube.

[0068] According to an embodiment of the present disclosure, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes, and in order to further improve the structural stability and electrical conductivity of the material, the carbon nanotubes are preferably single-walled carbon nanotubes.

[0069] According to an embodiment of the present disclosure, the multi-walled carbon nanotube comprises 2-10 walls, the multi-walled carbon nanotube has a concentric circle structure, and amorphous nanosilicon is distributed between at least some adjacent walls, the amorphous nanosilicon comprising silicon nanowires and / or nanosilicon particles.

[0070] According to an embodiment of the present disclosure, the silicon-carbon composite material satisfies at least one of the following:

[0071] a. The average diameter of the carbon nanotubes is 10-100 nm, preferably 20-60 nm, including but not limited to 10 nm, 20 nm, 25 nm, 30 nm, 33 nm, 39 nm, 43 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 80 nm, 90 nm, 100 nm, or a range consisting of any two of them;

[0072] b. The average length of the carbon nanotubes is 5-30 μm, preferably 18-28 μm, including but not limited to 3 μm, 5 μm, 8 μm, 12 μm, 15 μm, 20 μm, 23 μm, 30 μm, or a range consisting of any two of them;

[0073] c. The aspect ratio of the carbon nanotubes is 50-3000, preferably 300-1400, including but not limited to 50, 80, 150, 230, 350, 430, 450, 500, 600, 750, 930, 1000, 1200, 1400, 1500, 2000, 2500, 3000, or a range consisting of any two of them;

[0074] The diameters and lengths of all carbon nanotubes can be the same or different; the carbon nanotubes with the above structure are beneficial to electron diffusion and improve the electrical conductivity of the material.

[0075] According to an embodiment of the present disclosure, there is a gap in the carbon nanotube, the silicon nanowires in the tube are not aggregated, and the ratio of the total volume of the silicon nanowires to the total volume of the space in the carbon nanotube is 0.2-0.8, preferably 0.5-0.6. When the carbon nanotube is a multi-walled carbon nanotube, the "total volume of the space in the carbon nanotube" includes the sum of the volumes of all cavities in the carbon nanotube, and the "total volume of the silicon nanowires" refers to the total volume of the silicon nanowires in the material.

[0076] According to an embodiment of the present disclosure, amorphous nanosilicon is distributed in the outer wall of the carbon nanotube and / or in the carbon matrix, the amorphous nanosilicon comprising silicon nanowires and / or nanosilicon particles.

[0077] According to an embodiment of the present disclosure, the silicon-carbon composite particles further comprise a carbon coating layer, i.e. the silicon-carbon composite material has a structure of carbon nanotubes containing silicon nanowires + carbon matrix dispersion + carbon coating layer; the carbon coating layer coats the outside of the carbon nanotubes and the carbon matrix, and can completely coat or partially coat, and has a uniform thickness, the thickness being 5-25 nm, preferably 10-15 nm; the carbon coating layer can avoid exposure of the silicon nanowires, reduce the occurrence of silicon side reactions, and further improve the battery capacity.

[0078] According to an embodiment of the present disclosure, the silicon-carbon composite material satisfies at least one of the following:

[0079] A. The D50 particle size of the silicon-carbon composite material is 6-20 μm, preferably 10-15 μm;

[0080] B. The specific surface area of the silicon-carbon composite material is 0.3-3.0 m 2 / g, preferably 0.8-1.6 m 2 / g;

[0081] C. The powder conductivity of the silicon-carbon composite material is (1-10) x 10 5 S / m, preferably (6-9) x 10 5 S / m;

[0082] D. The silicon-carbon composite particles are spherical and / or spheroidal;

[0083] Wherein, the spherical and spheroidal are defined as conventional in the art.

[0084] In order to make the material have higher capacity and lower expansion rate, according to an embodiment of the present disclosure, the content of carbon elements in the silicon-carbon composite material is 50-80 w.t.%, preferably 50-60 w.t.%, including but not limited to 50 w.t.%, 55 w.t.%, 60 w.t.%, 62 w.t.%, 65 w.t.%, 70 w.t.%, 75 w.t.%, 78 w.t.% and the like, or a range formed by any two of them, and the "content of carbon elements" includes the content of all carbon elements in the material, i.e. the total content of carbon elements in the carbon nanotubes, the carbon matrix and the carbon coating layer.

[0085] According to an embodiment of the present disclosure, the silicon-carbon composite material contains a pre-lithiation material, i.e. the composite material contains lithium elements from the pre-lithiation step; in a further embodiment, the lithium elements in the pre-lithiation material are combined with the nanosilicon in the form of lithium ions, specifically, the lithium ions can be embedded in the silicon nanowires and / or nanosilicon particles, which is beneficial to further improve the initial efficiency of the battery.

[0086] A second aspect of this disclosure provides a method for preparing silicon-carbon composite materials, the method comprising the following steps:

[0087] S1. Deposit silicon atoms on graphene to convert the graphene into carbon nanotubes, and then form silicon nanowires in the carbon nanotubes to obtain a carbon nanotube-silicon nanowire composite material.

[0088] S2. The carbon nanotube-silicon nanowire composite material and the carbon source are mixed and granulated to obtain a silicon-carbon composite material.

[0089] The method disclosed herein first involves splitting silane gas into silicon atoms, followed by graphene coiling to form carbon nanotubes with silicon atoms deposited on their inner walls. In a subsequent step, the silicon atoms connect to form silicon nanowires, resulting in a carbon nanotube-silicon nanowire composite. This composite exhibits a structure where silicon nanowires are contained within carbon nanotubes. The carbon nanotube-silicon nanowire composite is then mixed with a carbon source and granulated to disperse the composite within a carbon matrix. This method allows for the preparation of silicon-carbon composite materials with specific structures through simple operational steps and is easily industrialized.

[0090] In this disclosure, in step S1, the silicon atoms deposited on the inner wall of the carbon nanotube can be small particles formed by a number of silicon atoms, and the maximum size of the small particles is smaller than the diameter of the carbon nanotube.

[0091] In this disclosure, in step S1, the silicon atoms forming the silicon nanowires may include silicon atoms deposited on graphene or silicon atoms not deposited on graphene, which enter the carbon nanotubes and connect with the silicon atoms inside the tubes to form silicon nanowires.

[0092] According to one embodiment of this disclosure, step S1 includes the following steps:

[0093] S11. The first silane gas is cracked, and silicon atoms are deposited on the graphene.

[0094] S12. Under the action of a catalyst and heating, the graphene is curled up and transformed into the carbon nanotube, and the silicon atoms are deposited on the inner wall of the carbon nanotube.

[0095] According to one embodiment of this disclosure, step S1 further includes the following steps:

[0096] S13. Silane gas is introduced into the carbon nanotube containing silicon atoms on the inner wall of the tube, so that the silicon atoms from the silane cracking are deposited on the tube wall of the carbon nanotube to form silicon nanowires.

[0097] According to one embodiment of this disclosure, in steps S11 and / or S12, the first silane gas drives the graphene to form a fluidized state.

[0098] In this disclosure, the first silane gas and the second silane gas respectively include one or more of SiH4, SiH3Cl, SiH2Cl2 and SiHCl3; preferably, the first silane gas and the second silane gas are the same type.

[0099] According to one embodiment of this disclosure, the method further includes: preparing the graphene using an electric arc method, the steps of which are conventional in the art, and the conditions include: a DC discharge current of 500-3000A, preferably 1200-1800A, including but not limited to 500A, 600A, 800A, 1000A, 1200A, 1500A, 1800A, 2300A, 3000A, or any combination thereof; an electric arc calcination temperature of 1000-3000℃; and a time of 30-90min, preferably 50-70min, including but not limited to 30min, 50min, 56min, 60min, 70min, 80min, 90min, or any combination thereof.

[0100] According to one embodiment of this disclosure, steps S11, S12 and S13 are performed in a fluidized bed.

[0101] According to one embodiment of this disclosure, step S11 includes: placing graphene in a fluidized bed and introducing a first silane gas and a carrier gas into the fluidized bed, causing the first silane gas to decompose and depositing silicon atoms on the graphene; the temperature of step S11 is 500-600°C, preferably 520-580°C; the time is 60-210 min, preferably 60-180 min, more preferably 90-150 min; the flow rate of the silane gas relative to 1 g of the graphene is 1.2-5.6 sccm, preferably 1.8-4.2 sccm. cm (i.e., the flow rate of silane gas per gram of graphene is 1.2-5.6 sccm, preferably 1.8-4.2 sccm); the carrier gas of the silane gas is an inert gas, including one or more of nitrogen, argon and helium. The above conditions can fully decompose the silane gas, which is beneficial to the formation of silicon nanowires; in a preferred embodiment, in step S11, the first silane gas drives the graphene to form a fluidized state, the silane decomposes to obtain silicon atoms, at least some of the silicon atoms are deposited on the graphene, and some silicon atoms may exist in the fluidized bed chamber.

[0102] According to one embodiment of this disclosure, step S12 includes: placing the catalyst into the fluidized bed of step S11, and under the action of the catalyst and heating, causing the graphene to curl up to form carbon nanotubes; in step S12, the catalyst includes one or more of elemental Pd, elemental Cu, elemental Co and elemental Ni; in step S12, the heating time is 200-500 min, preferably 280-420 min; the heating temperature is 400-460℃, preferably 420-450℃, and the amount of catalyst used is conventional in the art; in step S12, the first silane gas can be continuously introduced. In a preferred embodiment, in step S12, the first silane gas drives the graphene to a fluidized state, and the graphene curls up. Under the conditions of high temperature and catalyst, carbon-carbon bonds are formed at the edge of the graphene to form carbon nanotubes. Silicon atoms are deposited on the inner wall of the carbon nanotubes. During the formation of carbon nanotubes, some undeposited silicon atoms may also be drawn into the carbon nanotube wall, that is, silicon atoms may exist inside the carbon nanotubes.

[0103] According to one embodiment of this disclosure, the carbon nanotubes obtained in step S12 have a specific surface area of ​​50-150 m². 2 / g.

[0104] To ensure the material has a suitable silicon content, according to one embodiment of this disclosure, step S13 includes: introducing silane gas into a carbon nanotube containing silicon atoms on its inner wall, so that silicon atoms obtained from silane pyrolysis form silicon nanowires on the inner wall of the carbon nanotube and optionally in the inner cavity of the tube; the temperature of step S13 is 420-440℃, preferably 425-435℃; the time is 10-20h, preferably 12-18h; the flow rate of the silane gas relative to 1g of graphene is 3.6-8.5sccm, preferably 4.2-7.8sccm (i.e., the flow rate of the silane gas per gram of graphene is 3.6-8.5sccm, preferably 4.2-7.8sccm); the carrier gas of the second silane gas is an inert gas; in step S13, the silicon atoms obtained from silane pyrolysis form silicon nanowires, which are deposited on the tube wall of the carbon nanotube, reducing the specific surface area and surface activity of silicon.

[0105] In this disclosure, the time of steps S11 and S13 refers to the time when silane gas is introduced. For example, in step S11, the start of introducing silane gas is considered the start of step S11.

[0106] According to one embodiment of this disclosure, step S13 further includes: separating the silicon-carbon composite particles from the catalyst, wherein the separation method is conventional in the art, such as centrifugal fractionation or airflow fractionation.

[0107] In order to make carbon nanotubes uniformly dispersed in the carbon matrix, according to one embodiment of the present disclosure, in step S2, the mixing and granulation method includes spray drying granulation, with the following conditions: spray outlet temperature of 60-250°C, preferably 120-230°C; and time of 10-60 min, preferably 20-40 min.

[0108] According to one embodiment of this disclosure, the carbon source includes one or more of pitch, graphene, hard carbon, graphite, and carbon nanotubes.

[0109] According to one embodiment of this disclosure, the amount of carbon source, expressed in terms of carbon elements, is 40-50 w.t. relative to the total weight of the carbon nanotube-silicon nanowire composite material and the carbon source.

[0110] According to one embodiment of this disclosure, the method further includes carbon coating the particles obtained by the mixed granulation, wherein the carbon coating method includes asphalt carbonization or chemical vapor deposition coating.

[0111] According to one embodiment of this disclosure, the conditions for asphalt carbonization include: uniformly mixing silicon-carbon composite particles with asphalt, heating to 200-300°C for 2-5 hours, coating the surface of the silicon-carbon composite particles with liquid asphalt, and cooling to room temperature to form a carbon coating layer. The amount of asphalt used is 5-10 w.t. relative to the total weight of the silicon-carbon composite particles.

[0112] According to one embodiment of this disclosure, chemical vapor deposition coating is performed in a tube furnace under the following conditions: a temperature of 600-1200°C, a time of 1-5 hours, and a carbon source including one or more of methane, acetylene, and ethylene; the amount of carbon source used is 3-8 wt.% relative to the total weight of the silicon-carbon composite particles.

[0113] According to one embodiment of this disclosure, the method further includes: shaping the particles obtained by mixing and granulation before carbon coating, wherein the shaped material is a spherical particle with a D50 particle size of 6-20 μm; the shaping method includes: mechanical shaping, and the specific steps are conventional in the art.

[0114] According to one embodiment of this disclosure, in step S2, the mixing and granulation may further incorporate a lithium source for pre-lithiation. The lithium source includes one or more of lithium oxide, lithium nitride, lithium hydride, lithium hydroxide, and lithium carbonate. The amount of lithium source used is 2-5 wt.% relative to the total weight of the carbon nanotube-silicon nanowire composite material.

[0115] A third aspect of this disclosure provides a negative electrode comprising the silicon-carbon composite material described in the first aspect of this disclosure, or a silicon-carbon composite material prepared using the method described in the second aspect of this disclosure.

[0116] This disclosure provides a fourth aspect of a lithium-ion battery, the lithium-ion battery including the negative electrode described in the third aspect of this disclosure.

[0117] According to one embodiment of this disclosure, the lithium-ion battery further includes a separator, a positive electrode, and an electrolyte. The separator, positive electrode material, and electrolyte are conventional in the art and are not specifically required here.

[0118] The present invention will be described in detail below with reference to embodiments, but this does not constitute a limitation on the present invention.

[0119] The test methods involved in the following examples and comparative examples are as follows:

[0120] Methods and instrument for testing the average length of carbon nanotubes: The length of carbon nanotubes was observed using transmission electron microscopy imaging technology, and the average length of carbon nanotubes was statistically analyzed. The instrument model was FEI Titan Themis 200.

[0121] Test method and instrument model for average diameter: The diameter of carbon nanotubes was observed using transmission electron microscopy imaging technology, and the average diameter of carbon nanotubes was statistically analyzed. The instrument model was FEI Titan Themis 200.

[0122] The methods for testing the average length and average diameter of silicon nanowires are the same as those for carbon nanotubes;

[0123] The ratio of the total volume of silicon nanowires to the total internal volume of carbon nanotubes is calculated as follows: πr is the calculated value. 2 l / πR 2 L, where r and l are the average radius and average length of the silicon nanowire, and R and L are the average radius of the cavity and the average length of the carbon nanotube;

[0124] Test method and instrument model for carbon coating thickness: The test method for observing the thickness of carbon coating by transmission electron microscopy imaging technology and statistically analyzing the average thickness of carbon coating is FEI Titan Themis 200.

[0125] Test method and instrument model for particle size of silicon-carbon composite materials: The test is based on GB / T 19077-2016 Particle size distribution laser diffraction method. At room temperature, take an appropriate amount of sample (0.2g) and 10mL of anhydrous ethanol in a 100ml beaker, disperse ultrasonically for 5 minutes, and then test in the dispersion medium ethanol. The laser particle size analyzer irradiation optical path / volume is 25cm / 200mL.

[0126] Test method and instrument model for specific surface area: The test is based on GB / T 19587-2017 Gas Adsorption BET Method for Determination of Specific Surface Area of ​​Solid Substances. The sample degassing conditions are drying at 200℃ in vacuum for 120 minutes. The adsorbed gas is nitrogen with a purity of 99.99%. The instrument model is Beijing Best 3H-2000PS2.

[0127] Test method and instrument model for powder conductivity: Take 2g of powder material and place it in the fixture cavity of the powder resistivity meter. Use the four-probe method for testing. The test pressure is 10MPa and the holding time is 20s. The instrument model is Yuaneng Powder Resistivity Meter PRCD3100.

[0128] Test method and instrument model for carbon content: high-frequency heating infrared absorption method, instrument model CSY202201 carbon-sulfur analyzer.

[0129] Example 1

[0130] The silicon-carbon composite material A1 was prepared using the following steps:

[0131] (1) In an arc chamber filled with Ar inert gas, bring two graphite rod electrodes close together, raise an arc, set a DC discharge current of 1500A, an arc burning temperature of 2000℃, and a reaction time of 60min. Then pull the two graphite rod electrodes apart and collect the deposits on the inner wall of the reaction chamber.

[0132] (2) The graphene collected in the reaction chamber was placed in a fluidized bed at 550℃. SiH4 silane gas was introduced into the fluidized bed, and N2 inert gas was used as the carrier gas. The flow rate of silane gas was 3.1 sccm relative to 1g of graphene, and the time was 120min.

[0133] (3) N2 carrier gas and SiH4 silane gas were continuously introduced, and elemental Pd catalyst was added to the fluidized bed for 350 min at a temperature of 430 °C. Graphene rolled up to form carbon nanotubes with silicon atoms deposited on the inner wall, with a specific surface area of ​​110 m². 2 / g;

[0134] (4) N2 carrier gas and SiH4 silane gas were continuously introduced for 15 hours at a temperature of 430°C. The silane gas flow rate was 6.2 sccm relative to 1g of graphene.

[0135] (5) The carbon nanotube-silicon nanowire composite material obtained in step (4) is uniformly mixed with asphalt and spray-dried for granulation. The amount of asphalt used in terms of carbon element is 50 w.t.% relative to the total weight of the composite material and asphalt, the spray outlet temperature is 180℃, and the time is 30 min.

[0136] (6) The particles obtained by spray drying granulation were shaped to obtain particles with a D50 particle size of 13.6 μm, and then carbon coating was performed. The carbon coating method was chemical vapor deposition coating, and the conditions included: temperature of 900℃, time of 3h, carbon source of methane and acetylene mixed gas with a mixing volume of 1:1, and carbon source amount of 5.6 wt% relative to the total weight of particles, to obtain silicon-carbon composite material A1, the parameters of which are listed in Tables 1 and 2.

[0137] The silicon-carbon composite material prepared in Example 1 was subjected to SEM and XRD tests, and the results are shown in Figures 1 and 2.

[0138] As shown in Figure 2, the nano-silicon in silicon-carbon composite material A1 is amorphous silicon.

[0139] Example 2

[0140] Silicon-carbon composite material A2 was prepared using the method of Example 1, the only difference being that the DC discharge current in step (1) was 1000A. The D50 particle size and its parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0141] Example 3

[0142] Silicon-carbon composite material A3 was prepared using the method of Example 1, with the only difference being that the DC discharge current in step (1) was 2000A. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0143] Example 4

[0144] Silicon-carbon composite material A4 was prepared using the method of Example 1, with the only difference being that the reaction time in step (1) was 30 min. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0145] Example 5

[0146] Silicon-carbon composite material A5 was prepared using the method of Example 1, with the only difference being that the reaction time in step (1) was 90 min. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0147] Example 6

[0148] Silicon-carbon composite material A6 was prepared using the method of Example 1, with the only difference being that the temperature in the fluidized bed in step (2) was 500°C. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0149] Example 7

[0150] Silicon-carbon composite material A7 was prepared using the method of Example 1, with the only difference being that the temperature in the fluidized bed in step (2) was 600°C. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0151] Example 8

[0152] Silicon-carbon composite material A8 was prepared using the method of Example 1, with the only difference being that the gas introduction time in step (4) was 10h. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0153] Example 9

[0154] Silicon-carbon composite material A9 was prepared using the method of Example 1, with the only difference being that the gas introduction time in step (4) was 20h. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD testing showed that the nano-silicon was amorphous silicon.

[0155] Example 10

[0156] The silicon-carbon composite material A10 was prepared using the method of Example 1. The only difference was that lithium hydride (LiH) was added during the mixing process in step (5). The amount of lithium source used was 3 w.t.% relative to the total weight of the carbon nanotube-silicon nanowire composite material. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD tests showed that the nano-silicon was amorphous silicon.

[0157] Example 11

[0158] Silicon-carbon composite material A11 was prepared using the method of Example 1, except that step (6) was not performed. The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD tests show that the nano-silicon is amorphous silicon.

[0159] Transmission electron microscopy (TEM) tests on the silicon-carbon composite material prepared in the above embodiments show that it has a structure in which silicon nanowires are present within single-walled carbon nanotubes.

[0160] Comparative Example 1

[0161] The silicon-carbon composite material D1 was prepared using the method of Example 1. The only difference was that step (4) was not performed. Instead, carbon nanotubes with silicon atoms deposited on the inner wall obtained in step (3) were directly mixed with pitch and carried out step (5). The D50 particle size and parameters of the shaped particles are listed in Tables 1 and 2. XRD test showed that the nano-silicon was amorphous silicon. According to transmission electron microscopy, the nano-silicon did not have a silicon nanowire structure.

[0162] Comparative Example 2

[0163] The silicon-carbon composite material D2 was prepared using the method of Example 1. The only difference was that the reaction in step (5) was not carried out, and the product obtained in step (4) was directly coated with carbon in step (6). The parameters are listed in Tables 1 and 2. XRD test showed that the nano-silicon was amorphous silicon.

[0164] Table 1

[0165] Table 2

[0166] Test case

[0167] Battery fabrication: The composite materials prepared in the examples and comparative examples, as well as commercial silicon-carbon products, were used as negative electrode active materials. They were mixed with acetylene black and sodium carboxymethyl cellulose in a ratio of 8:1:1 and then coated onto copper foil to obtain the working electrode. A lithium metal sheet was used as the counter electrode. A PE / PP composite separator was used as the ion exchange membrane. A coin cell was fabricated using a weight ratio of LiPF6 (lithium hexafluorophosphate):EC (ethylene carbonate):EMC (ethyl methyl carbonate):DMC (dimethyl carbonate):DEC (diethyl carbonate):VC (ethylene carbonate):FEC (fluoroethylene carbonate) = 13.5:31:35:10:10:5:7) as the electrolyte. The results are listed in Table 3.

[0168] Charge and discharge performance test: The button cell was discharged to 0.005V at a constant current of 0.01C at room temperature, and then charged to 1.5V at a constant current of 0.1C. The discharge capacity and charge capacity of the battery were recorded, and the charge and discharge efficiency (%) was calculated as: charge capacity / discharge capacity × 100%.

[0169] Battery testing equipment: LANHE Blue Battery Testing System.

[0170] Expansion Test: Before assembling the coin cell, the original thickness of the electrode sheet for each sample group was measured using a micrometer. After initial discharge to 100% SOC, the coin cell was disassembled, the negative electrode sheet was removed, and cleaned with dichloromethane (DCM) solution. After drying, the thickness was measured to obtain the 100% SOC negative electrode sheet thickness. Initial expansion rate = 100% × (100% SOC negative electrode sheet thickness - original negative electrode sheet thickness) / original negative electrode sheet thickness.

[0171] Initial reversible capacity: Capacity of the first cycle of coin charging.

[0172] 100-cycle capacity retention: A coin cell is discharged at room temperature with a constant current of 0.01C to 0.005V, and then charged at a constant current of 0.1C to 1.5V. This is counted as one cycle. 100-cycle capacity retention = (Coin cell charging capacity on the 100th cycle / Coin cell charging capacity on the first cycle) × 100%.

[0173] Powder resistivity testing: The four-probe method is used, which uses four probes to measure the current and voltage on the powder sample, calculates the resistivity, and then obtains the powder conductivity.

[0174] Table 3

[0175] Based on the above data, it can be seen that using the silicon-carbon composite material disclosed herein as the negative electrode of a lithium-ion battery can achieve a lower expansion rate, higher battery capacity, and greater stability.

[0176] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0177] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0178] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes silicon-carbon composite particles; The silicon-carbon composite particles include a carbon matrix and carbon nanotubes distributed in the carbon matrix, wherein the carbon nanotubes contain silicon nanowires.

2. The silicon-carbon composite material according to claim 1, wherein, The silicon nanowires comprise amorphous silicon.

3. The silicon-carbon composite material according to claim 1 or 2, wherein, The silicon nanowires have an average diameter of 3-60 nm, and / or The average length of the silicon nanowires is 3-26 μm.

4. The silicon-carbon composite material according to any one of claims 1-3, wherein, The carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

5. The silicon-carbon composite material according to any one of claims 1-4, wherein, The silicon-carbon composite material satisfies at least one of the following: a. The average diameter of the carbon nanotubes is 10-100 nm; b. The average length of the carbon nanotubes is 5-30 μm; c. The aspect ratio of the carbon nanotubes is 50-3000.

6. The silicon-carbon composite material according to claim 4, wherein, The multi-walled carbon nanotubes comprise 2-10 tube walls, with amorphous silicon nanoparticles distributed between at least some of the adjacent tube walls. The amorphous silicon nanoparticles include silicon nanowires and / or silicon nanoparticles.

7. The silicon-carbon composite material according to any one of claims 1-6, wherein, The ratio of the total volume of the silicon nanowires to the total volume of the internal space of the carbon nanotubes is 0.2-0.

8.

8. The silicon-carbon composite material according to any one of claims 1-7, wherein, Amorphous silicon nanoparticles are distributed on the outer wall of the carbon nanotubes and / or within the carbon matrix, the amorphous silicon nanoparticles comprising silicon nanowires and / or silicon nanoparticles.

9. The silicon-carbon composite material according to any one of claims 1-8, wherein, The silicon-carbon composite particles also include a carbon coating layer; Optionally, the thickness of the carbon coating layer is 5-25 nm.

10. The silicon-carbon composite material according to any one of claims 1-9, wherein, The silicon-carbon composite material satisfies at least one of the following: A. The D50 particle size of the silicon-carbon composite material is 6-20 μm; B. The specific surface area of ​​the silicon-carbon composite material is 0.3-3.0 m². 2 / g; C. The powder conductivity of the silicon-carbon composite material is (1-10)×10⁻⁶. 5 S / m; D. The silicon-carbon composite particles are spherical and / or near-spherical.

11. The silicon-carbon composite material according to any one of claims 1-10, wherein, The carbon content in the silicon-carbon composite material is 50-80 wt%.

12. The silicon-carbon composite material according to any one of claims 1-11, wherein, The silicon-carbon composite material contains pre-lithiated materials.

13. The silicon-carbon composite material according to any one of claims 1-12, wherein, The carbon matrix includes amorphous carbon and / or graphite.

14. A method for preparing silicon-carbon composite materials, characterized in that, The method includes the following steps: S1. Deposit silicon atoms on graphene to convert the graphene into carbon nanotubes, and then form silicon nanowires in the carbon nanotubes to obtain a carbon nanotube-silicon nanowire composite material. S2. The carbon nanotube-silicon nanowire composite material and the carbon source are mixed and granulated to obtain a silicon-carbon composite material.

15. The method according to claim 14, wherein, Step S1 includes the following steps: S11. The first silane gas is cracked, and silicon atoms are deposited on the graphene. S12. Under the action of a catalyst and heating, the graphene is curled up and transformed into the carbon nanotube, and the silicon atoms are deposited on the inner wall of the carbon nanotube.

16. The method according to claim 15, wherein, Step S1 also includes the following steps: S13. A second silane gas is introduced into the carbon nanotubes obtained in step S12, so that the silicon atoms obtained by the cracking of the second silane gas and the silicon atoms deposited on the inner wall form silicon nanowires.

17. The method according to claim 15 or 16, wherein, In steps S11 and / or S12, the first silane gas drives the graphene to form a fluidized state.

18. The method according to claim 16, wherein, Steps S11, S12 and S13 are carried out in a fluidized bed; Optionally, the reaction temperature in step S11 is 500-600℃ and the reaction time is 60-210 min; Optionally, the flow rate of the first silane gas is 1.2-5.6 sccm relative to 1 g of the graphene.

19. The method according to any one of claims 15-18, wherein, In step S12, the catalyst includes one or more of elemental Pd, elemental Cu, elemental Co, and elemental Ni; In step S12, the heating time is 200-500 min and the heating temperature is 400-460℃; Optionally, the specific surface area of ​​the carbon nanotubes is 50-150 m². 2 / g.

20. The method according to claim 16 or 18, wherein, The reaction temperature in step S13 is 420-440℃, and the reaction time is 10-30h. The flow rate of the second silane gas is 3.6-8.5 sccm relative to 1g of the graphene.

21. The method according to any one of claims 14-20, wherein, In step S2, the mixing and granulation method includes spray drying granulation; Optionally, the spray drying granulation conditions meet the following requirements: spray outlet temperature is 60-250℃, and time is 10-60 min; Optionally, the carbon source includes one or more of pitch, graphene, hard carbon, graphite, and carbon nanotubes; Optionally, the amount of carbon source, expressed as elemental carbon, is 40-50 w.t.% relative to the total weight of the carbon nanotube-silicon nanowire composite material and the carbon source.

22. The method according to any one of claims 14-21, wherein, The method further includes carbon coating the particles obtained by the mixed granulation; Optionally, the carbon coating method includes bitumen carbonization or chemical vapor deposition coating.

23. A negative electrode, characterized in that, The negative electrode comprises the silicon-carbon composite material according to any one of claims 1-13, or the silicon-carbon composite material prepared by the method according to any one of claims 14-22.

24. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode as described in claim 23.

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