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

Abstract

A silicon-carbon composite material, a preparation method therefor, a negative electrode, and a battery, particularly relating to the technical field of batteries. The silicon-carbon composite material is formed from silicon-carbon composite material particles, the silicon-carbon composite material particles comprising a C / C composite porous material and silicon nanoparticles located in the pores and on the surface of the C / C composite porous material. The C / C composite porous material comprises a first carbon material and a second carbon material, the first carbon material being a porous carbon matrix, and the second carbon material penetrating through the inside of the C / C composite porous material and further penetrating through the silicon-carbon composite material. With respect to the provided silicon-carbon composite material, the C / C composite porous material is prepared by introducing the second carbon material, so that a conductive network having strength and flexibility is formed between the C / C composite porous material and the silicon nanoparticles, preventing the silicon from losing contact with the carbon substrate material when the volume changes, thus further improving the electronic conductivity and ionic conductivity of the silicon-carbon composite material and prolonging the service life of the material.

Description

Silicon-carbon composite material, preparation method thereof, negative electrode and battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to application number 202311154535X filed with the Patent Office of China on September 7, 2023, entitled “Silicon-carbon composite material, preparation method thereof, negative electrode and battery,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a silicon-carbon composite material, a preparation method thereof, a negative electrode, and a battery. Background Art

[0004] In recent years, the performance of silicon negative electrodes has been continuously improved, and Si / C composite negative electrode materials are facing industrialization, but the performance of silicon negative electrodes in all aspects still needs to be further improved.

[0005] The silicon negative electrode has the characteristics of high specific energy, but it also brings about huge volume expansion (about 300%) and contraction of silicon during the charge and discharge process. The composite of carbon material and silicon material can alleviate the volume effect of silicon during lithium insertion and removal to a certain extent. However, due to the repeated expansion and contraction of silicon volume, silicon and carbon are easily separated and lose contact. The intrinsic electronic conductivity of silicon is low, only 10 -5 ~10 -3 S / cm, and the lithium ion diffusion coefficient is also low, at 10 -14 ~10 -13 cm 2 / s, which will cause the structure and morphology of the silicon-carbon composite material to deteriorate and the internal resistance of the battery to increase, leading to failure problems such as a decrease in battery energy density, a decrease in voltage and power, and heat generation.

[0006] In view of this, the present disclosure is proposed.

[0007] Summary of the Invention

[0008] One of the purposes of the present disclosure is to provide a silicon-carbon composite material to solve the problem in the prior art that repeated expansion and contraction of silicon materials leads to loss of contact between silicon and carbon, resulting in degradation of the structural stability and electrochemical performance of the silicon-carbon composite material.

[0009] A second purpose of the present disclosure is to provide a method for preparing a silicon-carbon composite material.

[0010] A third object of the present disclosure is to provide a negative electrode.

[0011] A third object of the present disclosure is to provide a battery.

[0012] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions are adopted:

[0013] In a first aspect, the present disclosure provides a silicon-carbon composite material, which is composed of silicon-carbon composite material particles; the silicon-carbon composite material particles include a C / C composite porous material and silicon nanoparticles located in the pores and on the surface of the C / C composite porous material; the C / C composite porous material includes a first carbon material and a second carbon material; the first carbon material is a porous carbon matrix, and the second carbon material runs through the interior of the C / C composite porous material and further runs through the silicon-carbon composite material; the size of the second carbon material in at least one dimension is greater than 100 nm.

[0014] Furthermore, the second carbon material accounts for 0.01 to 10 wt.% in the C / C composite porous material, and the second carbon material includes at least one of carbon nanotubes, graphene, carbon black and carbon fibers.

[0015] Furthermore, the size of the second carbon material in the first dimension is L, which satisfies 100 nm<L<100 μm, and the size of the second carbon material in the second dimension is a, which satisfies 0<a<20 nm.

[0016] Furthermore, the L satisfies: 100 nm<L<20 μm, and the a satisfies: 0<a<10 nm.

[0017] Furthermore, the compacted specific surface area of ​​the silicon-carbon composite material is 1 to 20 times, preferably 1 to 10 times, and more preferably 1 to 5 times the specific surface area of ​​the silicon-carbon composite material.

[0018] Furthermore, the pore volume of the C / C composite porous material is 0.2 to 3.0 cm 3 / g, wherein the volume proportion of micropores is greater than 50%.

[0019] Furthermore, the pore volume of the C / C composite porous material is 0.4 to 1.5 cm 3 / g, of which the volume proportion of micropores is greater than 70%.

[0020] Furthermore, the diameter of the silicon nanoparticles is 0.5 to 5 nm. Furthermore, the content of silicon in the silicon-carbon composite material is 5 to 80 wt.%.

[0021] Furthermore, the silicon-carbon composite material particles also include heteroatoms X located in the pores of the C / C composite porous material, wherein the heteroatom X includes at least one of B, N, P, O and S. The heteroatom X forms Si-X chemical bonds with the silicon atoms in the silicon nanoparticles and separates and encapsulates the silicon nanoparticles.

[0022] Furthermore, the heteroatom content in the silicon-carbon composite material is 0 to 10 wt.%.

[0023] Furthermore, the surface of the silicon-carbon composite material particles has a coating layer; preferably, the material of the surface coating layer is selected from one or more of solid electrolytes, conductive polymers, carbonaceous materials, metals, alloys, metal oxides, metal halides, metal sulfides, metal phosphates, borates, sulfates, nitrates and polymetallic oxygen salts.

[0024] Furthermore, the surface of the silicon-carbon composite material particles has a coating layer with a grid structure. Preferably, the material of the coating layer includes at least one of carbon nanotubes, graphene, carbon black or carbon fiber.

[0025] Furthermore, the specific surface area of ​​the silicon-carbon composite material is 0.1 to 50 m 2 / g, pore volume is 0.01~0.5cm 3 / g.

[0026] Furthermore, the specific surface area of ​​the silicon-carbon composite material is 0.1 to 10 m 2 / g, pore volume is 0.01~0.1cm 3 / g.

[0027] Furthermore, the true density of the silicon-carbon composite material is 1.3 to 2.0 g / cm 3 , the closed pore volume is 0.01~0.25cm 3 / g.

[0028] The second aspect of the present disclosure provides a method for preparing a silicon-carbon composite material, comprising the following steps: step S1, providing a C / C composite porous material, wherein the C / C composite porous material comprises a first carbon material and a second carbon material; the first carbon material is a porous carbon matrix, and the second carbon material runs through the interior of the C / C composite porous material, and then runs through the silicon-carbon composite material; step S2, contacting a silicon-containing precursor with the C / C composite porous material, performing chemical vapor deposition, so that silicon nanoparticles are distributed in the pores and on the surface of the C / C composite porous material, to obtain the silicon-carbon composite material; wherein the C / C composite porous material, the first carbon material, the second carbon material and the silicon nanoparticles respectively have the same meanings as in the above-mentioned first aspect.

[0029] Furthermore, the method for preparing the C / C composite porous material is to introduce a second carbon material into at least one of the different preparation processes in the preparation process of the porous carbon material, wherein the preparation process includes a carbon precursor process, a carbon precursor pre-stabilization process, a carbonization process, a further pore-forming process, and a finished carbon material process;

[0030] Preferably, a first carbon material precursor and a second carbon material are mixed, and the mixture is sintered in an inert atmosphere or a mixed atmosphere of an inert gas and an oxygen-containing gas to obtain a C / C composite porous material; or, the first carbon material precursor is sintered in an inert atmosphere to obtain a first carbon material, and then the first carbon material and the second carbon material are mixed, and the mixture is sintered to obtain a C / C composite porous material; wherein the first carbon material precursor includes at least one of a polymer precursor, a biomass precursor and a fossil carbon source.

[0031] Furthermore, in step S2, when the silicon-containing precursor is brought into contact with the C / C composite porous material, a heteroatom-containing precursor is introduced; preferably, the contacting manner of the silicon-containing precursor and the heteroatom-containing precursor with the C / C composite porous material includes: (1) the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material alternately; or, (2) the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material at the same time; or, (3) the silicon-containing precursor and the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material alternately, or the silicon-containing precursor is continuously contacted with the C / C composite porous material, and the heteroatom-containing precursor is intermittently contacted with the C / C composite porous material; wherein, the temperature at which the silicon-containing precursor and the heteroatom-containing precursor are in contact with the C / C composite porous material is 150-1000°C, and the time is 1-100h.

[0032] Further, the silicon-containing precursor includes at least one of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, and silfluorene and its derivatives;

[0033] Furthermore, the heteroatom-containing precursor includes at least one of a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor, or a boron-containing precursor.

[0034] A third aspect of the present disclosure provides a negative electrode, comprising the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material obtained according to the preparation method described in the second aspect.

[0035] A fourth aspect of the present disclosure provides a battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material obtained according to the preparation method described in the second aspect.

[0036] Compared with the prior art, the present disclosure has at least the following beneficial effects:

[0037] The silicon-carbon composite material disclosed herein is prepared as a C / C composite porous material by introducing a second carbon material. This creates a strong and tough conductive network between the porous carbon matrix and the silicon nanoparticles, preventing silicon from losing contact with the porous carbon matrix during volume changes, thereby improving the electronic and ionic conductivity of the silicon-carbon composite material. The second carbon material acts as a reinforcing and toughening material, forming a flexible, restraining network that restricts silicon expansion while ensuring structural stability under low SOC conditions, thereby enhancing the cyclic and structural stability of the silicon-carbon composite material.

[0038] The present disclosure provides a method for preparing a silicon-carbon composite material. In the process of sintering and pore-forming activation, a first carbon material precursor loses small-molecule organic matter and releases small molecules such as CO2 and H2O to form a porous carbon matrix. At the same time, the second carbon material basically does not lose weight and form pores during the sintering and pore-forming process, and still retains its original size and structure, thereby forming a composite structure in which the second carbon material runs through the C / C composite porous material. After silicon is deposited inside the pores of the C / C composite porous material, a composite structure in which the second carbon material runs through the silicon-carbon composite material is formed. The silicon-carbon composite material thus obtained has the same beneficial effects as the silicon-carbon composite material provided above. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0040] FIG1 is a SEM image of the silicon-carbon composite material obtained in Example 6. DETAILED DESCRIPTION

[0041] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0042] The endpoints of the ranges and any values ​​disclosed in this disclosure 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0043] In a first aspect, the present disclosure provides a silicon-carbon composite material, which is composed of silicon-carbon composite material particles; the silicon-carbon composite material particles include a C / C composite porous material and silicon nanoparticles located in the pores and on the surface of the C / C composite porous material; the C / C composite porous material includes a first carbon material and a second carbon material; the first carbon material is a porous carbon matrix, and the second carbon material runs through the interior of the C / C composite porous material and further runs through the silicon-carbon composite material; the size of the second carbon material in at least one dimension is greater than 100 nm.

[0044] The silicon-carbon composite material provided herein is prepared into a C / C composite porous material by introducing a second carbon material. This creates a strong and tough conductive network between the porous carbon matrix and the silicon nanoparticles, preventing silicon from losing contact with the porous carbon matrix during volume changes, thereby improving the electronic and ionic conductivity of the silicon-carbon composite material. The second carbon material acts as a reinforcing and toughening material, forming a flexible, restraining network that restrains silicon expansion while ensuring structural stability under low SOC conditions, thereby enhancing the cyclic and structural stability of the silicon-carbon composite material.

[0045] The role of the second carbon material in the silicon-carbon composite material particles: ① Under low SOC conditions, the second carbon material forms conductive tentacles in the composite material, which connect the silicon nanoparticles and the porous carbon matrix to form a conductive path, avoiding the risk of silicon nanoparticles and the porous carbon matrix falling off due to the shrinkage of silicon nanoparticles under low load conditions, further improving the conductivity, and thus reducing the resistance DCIR of the battery system containing the composite material; ② Constructing a transmission channel and improving the rate performance; ③ The second carbon material is compounded with the first carbon material to form an elastic grid body, which improves the compressive strength of the material.

[0046] In some embodiments, the proportion of the second carbon material in the C / C composite porous material is 0.01 to 10 wt.%, and the second carbon material includes at least one of carbon nanotubes, graphene, carbon black and carbon fiber. The proportion of the second carbon material in the C / C composite porous material is greater than 10 wt.%, which will affect the uniformity of the pore distribution in the C / C composite porous material, and further affect the uniformity of silicon nanoparticles in the silicon-carbon composite material, resulting in a decrease in material performance; and the cost of the second carbon material is relatively high, and excessive introduction will increase the cost. Typically, but not limiting, the proportion of the second carbon material in the C / C composite porous material is 0.01%, 0.1 wt.%, 0.5 wt.%, 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, 9 wt.% or 10 wt.%, or a range value between any two values.

[0047] Furthermore, the size of the second carbon material in the first dimension is L, which satisfies 100nm<L<100μm, and the size of the second carbon material in the second dimension is a, which satisfies 0<a<20nm. Furthermore, the L satisfies: 100nm<L<20μm, and the a satisfies: 0<a<10nm. In three-dimensional space, the second carbon material satisfies the size L in the first dimension and the size a in the second dimension. In some specific embodiments, the second carbon material is, for example, a carbon nanotube (CNT), L is the length, and a is the diameter; for example, graphene, L is the length or width of the graphene plane, and a is the thickness of the sheet. The smaller the size a of the second carbon material in the second dimension, the better the flexibility and the higher the strength, the higher the stability of the formed C / C composite material, and thus the higher the stability of the silicon-carbon composite material, and the stronger the expansion constraint on silicon.

[0048] In some embodiments, since the material has strong mechanical strength and structural stability, it is easier to withstand pressure without damage. Therefore, the ratio of the compacted specific surface area of ​​the silicon-carbon composite material to the specific surface area of ​​the silicon-carbon composite material is small. The compacted specific surface area is the specific surface area of ​​the silicon-carbon composite material at 4000 kgf / cm 2 The specific surface area of ​​the material after compaction under pressure. The compacted specific surface area of ​​the silicon-carbon composite material (the silicon-carbon composite material at 4000kgf / cm 2 The specific surface area of ​​the material after compaction under pressure is 1 to 20 times, preferably 1 to 10 times, and more preferably 1 to 5 times the specific surface area of ​​the silicon-carbon composite material.

[0049] In some embodiments, the pore volume of the C / C composite porous material is 0.2 to 3.0 cm 3 / g, wherein the volume proportion of micropores is greater than 50%. Preferably, in some embodiments, the pore volume of the C / C composite porous material is 0.4-1.5 cm 3 / g, of which the volume proportion of micropores is greater than 70%.

[0050] In some embodiments, the diameter of the silicon nanoparticles is 0.5 to 5 nm; preferably, in some embodiments, the content of silicon in the silicon-carbon composite material is 5 to 80 wt.% (such as 5 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, 60 wt.%, 70 wt.% or 80 wt.% or a range between any two values).

[0051] In some embodiments, the silicon-carbon composite material particles further include heteroatoms X located within the pores of the C / C composite porous material. The heteroatoms X include at least one of B, N, P, O, and S. The heteroatoms X form Si-X chemical bonds with the silicon atoms in the silicon nanoparticles, separating and encapsulating the silicon nanoparticles. Preferably, in some embodiments, the heteroatom content in the silicon-carbon composite material is 0 to 10 wt.%.

[0052] In some embodiments, the surface of the silicon-carbon composite material particles has a coating layer; preferably, in some embodiments, the material of the surface coating layer is selected from one or more of solid electrolytes, conductive polymers, carbonaceous materials, metals, alloys, metal oxides, metal halides, metal sulfides, metal phosphates, borates, sulfates, nitrates and polymetallic oxygen salts.

[0053] Further preferably, in some embodiments, the carbonaceous material includes but is not limited to carbon nanotubes, graphene, carbon black or carbon fibers; in some embodiments, the organic polymer includes but is not limited to polyethylene oxide, polyethylene glycol, phenolic resin, epoxy resin or polysaccharide.

[0054] In some embodiments, the coating layer includes but is not limited to one or more of lithium hydroxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium metaphosphate, aluminum dihydrogen phosphate, lithium metaaluminate, lithium aluminum phosphate, aluminum phosphate, aluminum metaphosphate, aluminum oxide, aluminum oxide monohydrate, aluminum oxide trihydrate, aluminum hydroxide, aluminum sol, aluminum isopropoxide, magnesium oxide, magnesium hydroxide, zinc oxide, zinc hydroxide, titanium oxide, zirconium oxide, LiPON (lithium phosphorus oxynitride), LLZO (lithium lanthanum zirconium oxide), LATP (lithium titanium aluminum phosphate), LLTO (lithium lanthanum titanium oxide) and lithium germanium phosphorus sulfur compounds; in some embodiments, the coating layer includes but is not limited to one or more polymers such as polyethylene oxide, carboxymethyl cellulose, polyacrylic acid or polyacrylonitrile and lithium complexes thereof; in some embodiments, the coating layer includes but is not limited to one or more of LISICON-type solid electrolytes, NASICION-type solid electrolytes, perovskite-type solid electrolytes, garnet-type solid electrolytes and sulfide solid electrolytes; in some embodiments, the coating layer includes but is not limited to one or more of metal phosphates, borates, sulfates, nitrates and polymetallic oxyacids.

[0055] In some embodiments, the silicon-carbon composite material particles have a grid-structured coating on their surface. Preferably, the coating is made of at least one of carbon nanotubes, graphene, carbon black, or carbon fibers. The carbon material forms a grid-like structure on the composite material's surface, confining the volume expansion of the silicon nanoparticles within the material. The carbon material's network coating creates a conductive pathway, significantly reducing the composite material's resistivity. This stabilizes the interface and SEI film, reducing lithium ion consumption.

[0056] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 to 50 m 2 / g, pore volume is 0.01~0.5cm 3 / g. Preferably, in some embodiments, the specific surface area of ​​the silicon-carbon composite material is 0.1 to 10 m 2 / g, pore volume is 0.01~0.1cm 3 / g.

[0057] In some embodiments, the true density of the silicon-carbon composite material is 1.3 to 2.0 g / cm 3 , the closed pore volume is 0.01~0.25cm 3 / g.

[0058] The second aspect of the present disclosure provides a method for preparing a silicon-carbon composite material, comprising the following steps: step S1, providing a C / C composite porous material, wherein the C / C composite porous material comprises a first carbon material and a second carbon material; the first carbon material is a porous carbon matrix, and the second carbon material runs through the interior of the C / C composite porous material, and then runs through the silicon-carbon composite material; step S2, contacting a silicon-containing precursor with the C / C composite porous material, performing chemical vapor deposition, and distributing silicon nanoparticles in the pores and on the surface of the C / C composite porous material to obtain the silicon-carbon composite material; wherein the C / C composite porous material, the first carbon material, the second carbon material and the silicon nanoparticles respectively have the same meanings as in the above-mentioned first aspect.

[0059] The present disclosure provides a method for preparing a silicon-carbon composite material. In the process of sintering and pore-forming activation, a first carbon material precursor loses small-molecule organic matter and releases small molecules such as CO2 and H2O to form a porous carbon matrix. At the same time, the second carbon material basically does not lose weight and form pores during the sintering and pore-forming process, and still retains its original size and structure, thereby forming a composite structure in which the second carbon material runs through the C / C composite porous material. After silicon is deposited inside the pores of the C / C composite porous material, a composite structure in which the second carbon material runs through the silicon-carbon composite material is formed. The silicon-carbon composite material thus obtained has the same beneficial effects as the silicon-carbon composite material provided above.

[0060] In some embodiments, the preparation method of C / C composite porous material is to introduce a second carbon material into at least one of the different preparation processes in the preparation process of porous carbon material, and the preparation process includes a carbon precursor process, a carbon precursor pre-stabilization process, a carbonization process, a further pore-forming process and a finished carbon material process, etc.

[0061] Preferably, in some embodiments, the first carbon material precursor and the second carbon material are mixed, and the mixture is sintered in an inert atmosphere or a mixed atmosphere of an inert gas and an oxygen-containing gas to obtain a C / C composite porous material.

[0062] In other embodiments, the preparation method of the C / C composite porous material includes: sintering a first carbon material precursor in an inert atmosphere to obtain a first carbon material, then mixing the first carbon material and a second carbon material, and sintering the mixture to obtain a C / C composite porous material.

[0063] In some embodiments, during the preparation of the C / C composite porous material, a pore-forming agent may be added to the first carbon material precursor to form a porous carbon matrix having a rich pore structure after sintering. The pore-forming agent is selected from one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, oleic acid, oleylamine, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (e.g., P123, F127, and / or F108), citric acid, malic acid, succinic acid, NH4HCO3, (NH4)2CO3, HNO3, H2SO4, LiOH, NaOH, and KOH.

[0064] In some embodiments, the first carbon material precursor includes at least one of a polymer precursor, a biomass precursor, and a fossil carbon source. For example, the first carbon material precursor may be, but is not limited to, one or more of glucose, sucrose, maltose, lactose, cyclodextrin, starch, glycogen, cellulose, hemicellulose, lignin, epoxy resin, thermoplastic phenolic resin, thermosetting phenolic resin, polyoxymethylene resin, urea-formaldehyde resin, furfural resin, furfural ketone resin, acrylic resin, coconut shell, rice husk, and wood.

[0065] In some embodiments, the above-mentioned step of preparing the C / C composite porous material further includes activating and pore-forming the obtained C / C composite porous material, specifically: contacting the C / C composite porous material with an oxygen-containing substance, wherein the oxygen-containing substance includes but is not limited to gases such as H2O, CO2 and O2, solids such as KOH, NaOH, K2CO3, Na2CO3, potassium aldehyde and sodium acetate and their aqueous solutions, and H3PO4 or its aqueous solution, and the contact mode includes gas-solid contact, solid-solid contact and solid-liquid contact, and the contact temperature is 300-1200°C (such as 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C or any temperature therebetween), preferably 600-900°C.

[0066] In some embodiments, the temperature of the contact between the silicon-containing precursor and the C / C composite porous material in step S2 is 150° C. to 1000° C., and the time is 1 to 100 hours.

[0067] In some embodiments, a heteroatom-containing precursor is introduced when the silicon-containing precursor is contacted with the C / C composite porous material in step S2; preferably, the contact manner of the silicon-containing precursor and the heteroatom-containing precursor with the C / C composite porous material includes: (1) the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material alternately; or, (2) the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material at the same time; or, (3) the silicon-containing precursor and the silicon-containing precursor and the heteroatom-containing precursor are contacted with the C / C composite porous material alternately, or the silicon-containing precursor is continuously contacted with the C / C composite porous material, and the heteroatom-containing precursor is intermittently contacted with the C / C composite porous material.

[0068] Furthermore, the temperature of the silicon-containing precursor and the heteroatom-containing precursor in contact with the C / C composite porous material is 150°C to 1000°C (such as 150°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C or any temperature therebetween), and the time is 1 to 100h (such as 1h, 12h, 24h, 36h, 48h, 72h, 96h or 100h or any time therebetween).

[0069] In some embodiments, the silicon-containing precursor includes at least one of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, and silfluorene and its derivatives.

[0070] In some embodiments, heteroatom-containing precursors include, but are not limited to, any one or a mixture of two or more of a boron-containing precursor, a nitrogen-containing precursor, a phosphorus-containing precursor, an oxygen-containing precursor, and a sulfur-containing precursor. The boron-containing precursor includes B(CH3)3; the nitrogen-containing precursor includes NH3, NO, N2O, and acetonitrile; the phosphorus-containing precursor includes PH3 and POCl3; the oxygen-containing precursor includes oxygen, carbon dioxide, water vapor, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, and butanone; and the sulfur-containing precursor includes any one or a mixture of two or more of H2S and SO2.

[0071] A third aspect of the present disclosure provides a negative electrode, which includes the silicon-carbon composite material provided by the first aspect or the silicon-carbon composite material obtained according to the preparation method provided by the second aspect.

[0072] A fourth aspect of the present disclosure provides a battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises the silicon-carbon composite material provided in the first aspect or the silicon-carbon composite material prepared according to the preparation method provided in the second aspect. By employing this silicon-carbon composite material, the battery's energy density is effectively increased, its internal resistance is reduced, and it has broad application prospects.

[0073] The present disclosure is further illustrated below by specific examples and comparative examples. However, it should be understood that these examples are merely for the purpose of further explanation and are not to be construed as limiting the present disclosure in any manner. The raw materials used in the examples and comparative examples herein, unless otherwise specified, were prepared under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, for which the manufacturer is not specified, are all commercially available conventional products.

[0074] Example 1

[0075] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0076] (1) Sucrose and single-walled carbon nanotubes (DaZhan Nano (Guangdong) Co., Ltd., outer diameter range 1.6±0.4nm, length ≥5μm) were mixed in a mass ratio of 100 / 0.01. The resulting mixture was heated from room temperature to 800℃ at 2℃ / min in a N2 atmosphere and kept at this temperature for 2h. The resulting material was crushed and graded, mixed with KOH at m(KOH):m(C)=1:2, and activated at 800℃ for 2h to obtain a C / C composite porous material. The proportion of carbon nanotubes in the porous composite skeleton was 0.1wt.%, and the pore volume of the C / C composite porous material was 0.80cm 3 / g, and the volume of micropores accounts for 85% of the pore volume.

[0077] (2) The C / C composite porous material was placed in a tube furnace and heated from room temperature to 600°C at a rate of 2°C / min in a N2 atmosphere; then the temperature was changed to a 20% SiH4-N2 mixed gas and maintained at 600°C in the 20% SiH4-N2 mixed atmosphere for 30 hours; after changing to a N2 atmosphere, the temperature was naturally lowered, crushed and graded to obtain a silicon-carbon composite material. The silicon content in the silicon-carbon composite material was 52 wt.%.

[0078] Example 2

[0079] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0080] (1) The difference from this step in Example 1 is that the proportion of single-walled carbon nanotubes in the C / C composite porous material is 0.01 wt.%, and the remaining raw materials and methods are the same as those in this step in Example 1, which will not be repeated here.

[0081] (2) Same as Example 1.

[0082] Example 3

[0083] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0084] (1) The difference from this step in Example 1 is that the proportion of single-walled carbon nanotubes in the C / C composite porous material is 0.5 wt.%, and the remaining raw materials and methods are the same as those in this step in Example 1, which will not be repeated here.

[0085] (2) Same as Example 1.

[0086] Example 4

[0087] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0088] (1) The difference from this step in Example 1 is that graphene (Toray New Materials (Guangdong) Co., Ltd., sheet thickness <15 nm, length or width of graphene plane is 3 to 6 μm) is used to replace single-walled carbon nanotubes, and the proportion of graphene in the porous composite skeleton is 2 wt.%. The remaining raw materials and methods are the same as those in this step in Example 1 and are not repeated here.

[0089] (2) Same as Example 1.

[0090] Example 5

[0091] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0092] (1) Same as Example 1.

[0093] (2) The C / C composite porous material was placed in a tubular furnace and heated from room temperature to 600°C at a rate of 2°C / min in a N2 atmosphere; then the temperature was changed to a 20% SiH4-0.002% CO2-N2 mixed gas and maintained at 600°C for 30 h in a 20% SiH4-N2 mixed atmosphere; after changing to a N2 atmosphere, the temperature was naturally lowered, crushed and graded to obtain a silicon-carbon composite material.

[0094] Example 6

[0095] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0096] (1) Same as Example 1.

[0097] (2) Same as Example 1.

[0098] (3) The silicon-carbon composite material particles were evenly dispersed in pure water, and then 0.4% by mass of CNT (the manufacturer and model of the single-walled carbon nanotubes in Example 1 were the same) were added, stirred evenly, and then spray-dried to obtain a CNT-coated silicon-carbon composite material.

[0099] Example 7

[0100] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0101] (1) Same as Example 1.

[0102] (2) Same as Example 1.

[0103] (3) The silicon-carbon composite material particles were evenly dispersed in pure water, and then 1% by mass of CNT (the manufacturer and model of the single-walled carbon nanotubes in Example 1 were the same) and 3% by mass of lithium phosphate were added. After stirring evenly, the mixture was filtered and dried to obtain a silicon-carbon composite material with a composite fast ion conductor coating layer. The mass ratio of CNT to lithium phosphate was 0.3:1, and the thickness of the coating layer was 6 nm, thereby obtaining a silicon-carbon composite material.

[0104] Example 8

[0105] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0106] (1) The difference from this step in Example 1 is that multi-walled carbon nanotubes (Beijing Zhongke Leiming Technology Co., Ltd., outer diameter 30-60 nm, inner diameter 20-50 nm, length 1-10 μm) are used to replace single-walled carbon nanotubes. The proportion of carbon nanotubes in the porous composite skeleton is 10 wt.%. The remaining raw materials and methods are the same as those in this step in Example 1 and are not repeated here.

[0107] (2) Same as Example 1.

[0108] Example 9

[0109] This embodiment provides a silicon-carbon composite material, and the preparation method is as follows:

[0110] (1) The difference from this step in Example 1 is that multi-walled carbon nanotubes (Shenzhen Turing New Materials Co., Ltd., diameter 3-15 nm, length 15-30 μm) are used to replace single-walled carbon nanotubes, and the proportion of carbon nanotubes in the porous composite skeleton is 5 wt.%. The remaining raw materials and methods are the same as those in this step in Example 1 and are not repeated here.

[0111] (2) Same as Example 1.

[0112] Example 10

[0113] (1) Sucrose and single-walled carbon nanotubes (DaZhan Nano (Guangdong) Co., Ltd., outer diameter range 1.6±0.4nm, length ≥5μm) were mixed in a mass ratio of 100 / 0.01. The resulting mixture was heated from room temperature to 800℃ at 2℃ / min in a N2 atmosphere and maintained at this temperature for 2h. The resulting material was crushed and graded, mixed with KOH at m(KOH):m(C)=1:2, and activated at 800℃ for 0.5h to obtain a C / C composite porous material. The proportion of carbon nanotubes in the porous composite skeleton was 0.15wt.%, and the pore volume of the C / C composite porous material was 0.40cm 3 / g, and the volume of micropores accounts for 88% of the pore volume.

[0114] (2) The C / C composite porous material was placed in a tube furnace and heated from room temperature to 600°C at 2°C / min in a N2 atmosphere; then the temperature was changed to a 10% SiH4-N2 mixed gas and maintained at 600°C in a 10% SiH4-N2 mixed atmosphere for 10 hours; after changing to a N2 atmosphere, the temperature was naturally lowered; after reaching room temperature, dry air was introduced, and after 2 hours, the temperature was slowly increased to 200°C and maintained in an air atmosphere for 2 hours; the temperature was increased to 600°C in a N2 atmosphere, and then the temperature was changed to 10% C2H2-N2 and maintained for 2 hours. The obtained material was crushed and graded to obtain a silicon-carbon composite material. The silicon content in the obtained silicon-carbon composite material was 8 wt.%.

[0115] Example 11

[0116] (1) Sucrose and single-walled carbon nanotubes (DaZhan Nano (Guangdong) Co., Ltd., outer diameter range 1.6±0.4nm, length ≥5μm) were mixed in a mass ratio of 100 / 0.01. The resulting mixture was heated from room temperature to 800℃ at 2℃ / min in a N2 atmosphere and maintained at this temperature for 2h. The resulting material was crushed and graded, mixed with KOH at m(KOH):m(C)=1:2, and activated at 800℃ for 5h to obtain a C / C composite porous material. The proportion of carbon nanotubes in the porous composite skeleton was 0.06wt.%, and the pore volume of the C / C composite porous material was 1.50cm 3 / g, and the volume of micropores accounts for 86% of the pore volume.

[0117] (2) This step differs from that in Example 1 in that the volume content of SiH₄ in the SiH₄-N₂ gas mixture is changed to 30%, and the deposition time is changed to 40 h. The remaining raw materials and methods are the same as those in Example 1 and are not described here. The silicon content in the resulting silicon-carbon composite material is 78 wt.%.

[0118] Comparative Example 1

[0119] This comparative example provides a silicon-carbon composite material, and the preparation method is as follows:

[0120] (1) Sucrose was heated from room temperature to 800°C at a rate of 2°C / min in a nitrogen atmosphere and maintained at this temperature for 2 h. The resulting material was crushed and graded, mixed with KOH at a ratio of m(KOH):m(C)=1:2, and activated at 800°C for 2 h to obtain porous carbon.

[0121] (2) The porous carbon was placed in a tubular furnace and heated from room temperature to 600°C at a rate of 2°C / min in a N2 atmosphere; then the mixture was changed to a 20% SiH4-N2 mixed gas and maintained at 600°C for 30 h in the 20% SiH4-N2 mixed atmosphere; after changing to a N2 atmosphere, the mixture was naturally cooled, crushed and graded to obtain a silicon-carbon composite material.

[0122] Test Example 1

[0123] The physicochemical parameters of the silicon-carbon composite materials obtained in Examples 1 to 9 and Comparative Example 1 were measured.

[0124] The specific surface area of ​​the particles was tested by a specific surface area analyzer.

[0125] The true density of the particles was tested by a fully automatic true density meter.

[0126] Compacted specific surface area: Powder was placed into a 12 mm diameter mold and subjected to 4000 kgf / cm 2Apply pressure and maintain it for 30 s. Test the specific surface area of the compacted material, which is denoted as the compacted specific surface area. The smaller the ratio between the compacted specific surface area and the specific surface area, the stronger the compressive ability of the material.

[0127] The obtained data are shown in Table 1.

[0128] Table 1 Physical and chemical parameter table of silicon-carbon composite materials

[0129] As can be seen from Table 1, Examples 1 to 11 have a lower ratio of compacted specific surface area to specific surface area compared with the comparative example, indicating that the silicon-carbon composite materials obtained by chemical vapor deposition of silicon with the C / C composite material added with the second carbon material as the matrix have higher compressive strength. The electrodes prepared from the materials of the examples will exhibit higher cycle stability. Among them, the improvement of the compressive strength of the material is more obvious with single-walled carbon nanotubes and graphene with smaller sizes in the second dimension. For example, the ratio of the compacted specific surface area to the specific surface area in Examples 1 to 6 is less than that in Examples 8 and 9. Correspondingly, its electrochemical performance is slightly worse. Example 5 was subjected to CO2 passivation treatment relative to Example 1. Its weaker oxidizing property makes some silicon nanoparticles be wrapped by oxygen-containing substances such as SiO x substances (0 < x < 1), so the composite material exhibits higher compressive strength. Example 6 was subjected to CNT coating on the basis of Example 1, further improving the compressive strength of the composite material. Example 7 was added with lithium phosphate coating on the basis of Example 1, that is, CNT and lithium phosphate composite coating; Examples 8 and 9 used multi-walled tubes with larger diameters instead of single-walled CNTs for coating. The wall carbon nanotubes have a thicker diameter and greatly reduced flexibility. A higher addition amount is required to form a suitable conductive network in the composite material, and the compacted density of the material is reduced, which will further affect its electrochemical stability. Examples 10 and 11 are cases of lower and higher silicon contents respectively. When the silicon content is low, the pore volume of the required C / C composite porous material substrate is small. Therefore, the CNT content in the C / C composite porous material obtained with the same proportion of CNT addition amount in the precursor is large, and thus the CNT content in the final silicon-carbon composite material is also large. This material has the smallest compacted specific surface area, that is, the composite material has the highest anti-compaction strength. The porous carbon matrix of Comparative Example 1 does not contain the second carbon material, and the specific surface area of the obtained silicon-carbon composite material after compaction under a pressure of 4000 kgf / cm 2 increases to 92 m 2 / g. It can be seen that the pressure resistance strength of this composite material is very low, which will greatly affect its cycle stability in lithium-ion batteries.

[0130] Test Example 2

[0131] The silicon-carbon composite material provided in Example 6 was observed by field emission scanning electron microscopy, and the resulting SEM photograph is shown in Figure 1. As can be seen from Figure 1, CNTs are coated on the outside of the particles, forming an interlaced conductive network. The presence of the second carbon material is not easily observed directly in the SEM images of Examples 1 to 5, because the second carbon material, such as CNTs or graphene, has a diameter or thickness of less than 10 nm or even less than 3 nm, and is tightly connected to the first carbon material in the C / C composite porous material, and is usually located inside the composite material, making it difficult to observe the second carbon material on the surface of the composite material.

[0132] Test Example 3

[0133] The powder resistivity of the silicon-carbon composite materials obtained in Examples 1 to 9 and Comparative Example 1 was tested under a pressure of 20 MPa using a ST2722-SZ four-probe powder resistivity tester produced by Suzhou Jingge Electronics Co., Ltd. The obtained data are shown in Table 2.

[0134] Test Example 4

[0135] The silicon-carbon composite materials obtained in Examples 1 to 9 and Comparative Example 1 were used as negative electrode active materials to prepare negative electrode sheets, and CR2032 button batteries were prepared using conventional methods. The electrical performance of the batteries was tested. The specific test method is as follows:

[0136] (1) Half-cell assembly: CR2032 button cells were assembled in a glove box, with a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and the electrolyte being a mixture of LiPF6 dissolved in ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), where the LiPF6 concentration was 1 mol / L.

[0137] The battery was tested for charge and discharge using the LAND battery testing system.

[0138] (2) Gram capacity and initial efficiency test: After the CR2032 battery is uncharged and left to stand for 6 hours, it is discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V; after standing for 5 minutes, it is charged at a constant current of 0.05C to 1.5V; the gram capacity of the first delithiation is the gram capacity (or mass specific capacity) of the electrode material.

[0139] The obtained data are shown in Table 2.

[0140] Test Example 5

[0141] The silicon-carbon composite materials obtained in Examples 1 to 9 and Comparative Example 1 were used as the negative electrode active material. The electrodes containing the negative electrode active material were prepared using conventional methods to prepare soft-pack batteries and undergo electrical performance testing. The soft-pack batteries were prepared in a dehumidified room with a dew point of -45°C. The batteries were subjected to charge and discharge cycle testing using a LANBTS battery testing system. The specific testing method is as follows:

[0142] (1) Preparation of positive electrode sheet: The positive electrode active material NCM811, the conductive agent SuperP, the binder PVDF and the solvent NMP were stirred and mixed in a mass ratio of 92:3:5:150, and then evenly coated on the positive electrode current collector, and then dried at 80°C to obtain the positive electrode sheet.

[0143] (2) Preparation of negative electrode sheet: The silicon-carbon composite materials obtained in Examples 1 to 9 and Comparative Example 1 were mixed with graphite to obtain a negative electrode active material. The negative electrode active material, conductive agent Super P, binder polyacrylic acid, and solvent deionized water were stirred and uniformly mixed in a mass ratio of 95:1:4:120, and then evenly coated on the negative electrode current collector. The mixture was then dried at 100°C to obtain a negative electrode sheet.

[0144] (3) The positive and negative electrodes are stacked in a square shape and separated by a polypropylene separator to form a battery core. The core is then encapsulated in an aluminum-plastic bag. An electrolyte of the corresponding capacity is injected into the bag and vacuum-sealed to obtain a soft-pack battery. The electrolyte is a mixture of LiPF6, EC, and DEC, with a LiPF6 concentration of 1 mol / L and a volume ratio of EC to DEC of 1:1.

[0145] (4) Formation: After filling and sealing, the battery begins to form. It is placed in a 25°C constant temperature box for 12 hours, then charged to 3.3V at 0.02C constant current, allowed to stand for 30 minutes, charged to 3.8V at 0.025C constant current, allowed to stand for 10 minutes, and charged to 4.2V at 0.33C constant current. The formed battery is vacuumed and the air bag is sheared, and then the capacity is divided. It is charged to 4.45V at 0.33C constant current, allowed to stand for 10 minutes, discharged to 3V at 1C constant current, allowed to stand for 10 minutes, and discharged to 3V at 0.33C constant current. The capacity division is completed. The ratio of the discharge capacity divided by the charge capacity in the soft pack battery formation is the battery's first coulombic efficiency.

[0146] (5) 25℃ cycle test: Place the battery in a 25℃ constant temperature box, charge it to 4.45V at a constant current of 1C, and then charge it to 0.1C at a constant voltage of 4.45V; after standing for 10 minutes, discharge it to 3.0V at a constant current of 1C, and stand it for 10 minutes. Repeat the above charging and discharging steps until the discharge capacity is lower than 80% of the discharge capacity of the first cycle. The number of cycles obtained at this time is the cycle life of the soft-pack battery; this records the capacity retention rate after 100 cycles.

[0147] (6) Rate performance test: The prepared button-type full battery was left to stand at room temperature for 12 hours, and then subjected to constant current charge and discharge test on a blue electric test system with a charge and discharge cut-off voltage of 3.0 to 4.25V. The battery was first charged and discharged at a current of 0.25C for three cycles. Then, the battery was charged and discharged at a current of 0.5C for three cycles. Finally, the battery was charged and discharged at a current of 1C for three cycles. The capacity retention rate was calculated by dividing the discharge capacity of the 9th cycle by the discharge capacity of the 1st cycle by 100%. A higher value is considered to have better rate performance.

[0148] (7) DCIR test: Place the battery after disassembly in a constant temperature box at 25℃, charge it to 4.45V at 1C constant current, record the charging capacity as Q1, let it stand for 10 minutes, discharge it to 3.0V at 1C constant current, and let it stand for 10 minutes. Continue to charge it to the capacity Q2 (Q2 = Q1 * 10%) at 1C constant current, that is, the battery capacity reaches 10% SOC. After standing for 10 minutes, first record the battery voltage at this time as U0, discharge it at 5C constant current for 18s, and record the battery voltage at this time as U1. The discharge DC internal resistance of the battery at 10% SOC is DCIR = (U0-U1) / 5C.

[0149] The obtained data are shown in Table 2.

[0150] Table 2 Electrical performance data

[0151] As can be seen from Table 2, the silicon content in the silicon-carbon composite materials obtained in Examples 1 to 11 and Comparative Example 1 is not much different, so the gram capacity is close. Compared with Comparative Example 1, due to the introduction of the second carbon material, a conductive network is constructed in the C / C composite porous material, and the resistivity and DCIR of the silicon-carbon composite material in Examples 1 to 11 are significantly lower than those in Comparative Example 1. At the same time, the ion conductivity of the silicon-carbon composite material is also improved, which is reflected in the rate performance being significantly higher than that in Comparative Example 1. Among them, the surfaces of the silicon-carbon composite materials obtained in Examples 6 and 7 have a CNT coating layer and a composite coating layer of CNT and lithium phosphate, respectively, and the optimization of their resistivity, rate performance and DCIR is more significant. The second carbon material has good flexibility, which can increase the strength of the silicon-carbon composite material, improve the structural stability of the material, and thus improve the cycle stability. Therefore, the first coulombic efficiency and the cycle capacity retention rate after 100 cycles of the silicon-carbon composite materials obtained in Examples 1 to 11 are higher than those in Comparative Example 1.

[0152] Compared to Examples 8 and 9, Examples 1 to 3 use single-walled carbon nanotubes as the second carbon material. Compared to multi-walled carbon nanotubes, single-walled carbon nanotubes have a higher Young's modulus. At the same time, single-walled carbon nanotubes have a smaller diameter, better flexibility, and higher strength. The resulting C / C porous composite material has higher stability, and thus the silicon-carbon composite material has higher stability. Therefore, the cyclic stability of the composite materials of Examples 1 to 3 is better than that of Examples 8 and 9. In Example 8, the multi-walled carbon nanotubes have a larger diameter and greatly reduced flexibility. A higher addition amount is required to form a suitable conductive network in the composite material, resulting in the formation of more closed pores in the composite material, a lower compaction density of the material, and a decrease in structural stability during cycling.

[0153] Compared with Example 1, Example 5 introduces the doping element O to separate and wrap the silicon nanoparticles, thereby improving the electrical conductivity and ion conductivity of the silicon region, and the rate performance is higher than that of Example 1.

[0154] Examples 10 and 11 represent lower and higher silicon content, respectively. The composite material in Example 10 has a lower silicon content, resulting in a lower specific capacity. However, due to its relatively higher CNT content, its rate capability, resistivity, and DCIR are all very low, and the material exhibits excellent cycling stability. Example 11 has a higher silicon content, resulting in a higher specific capacity, but its cycling stability is relatively poor compared to Example 10.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure. Industrial Applicability

[0156] The method disclosed herein improves the cyclic stability and structural stability of the silicon-carbon composite material, and is conducive to the industrialization of the silicon-carbon composite material.

Claims

1. A silicon-carbon composite material, characterized in that: It is composed of silicon-carbon composite particles; The silicon-carbon composite material particles include a C / C composite porous material and silicon nanoparticles located in the pores and on the surface of the C / C composite porous material; The C / C composite porous material includes a first carbon material and a second carbon material; The first carbon material is a porous carbon matrix, and the second carbon material runs through the interior of the C / C composite porous material and further runs through the silicon-carbon composite material; The size of the second carbon material in at least one dimension is greater than 100 nm.

2. The silicon-carbon composite material according to claim 1, characterized in that: The proportion of the second carbon material in the C / C composite porous material is 0.01 to 10 wt.%, and the second carbon material includes at least one of carbon nanotubes, graphene, carbon black and carbon fibers; Preferably, the size of the second carbon material in the first dimension is L, satisfying 100 nm<L<100 μm, and the size of the second carbon material in the second dimension is a, satisfying 0<a<20 nm; Further preferably, the L satisfies: 100 nm<L<20 μm, and the a satisfies: 0<a<10 nm.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The compacted specific surface area of ​​the silicon-carbon composite material is 1 to 20 times, preferably 1 to 10 times, and more preferably 1 to 5 times the specific surface area of ​​the silicon-carbon composite material.

4. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The pore volume of the C / C composite porous material is 0.2 to 3.0 cm 3 / g, where the volume proportion of micropores is greater than 50%; Preferably, the pore volume of the C / C composite porous material is 0.4 to 1.5 cm 3 / g, of which the volume proportion of micropores is greater than 70%.

5. The silicon-carbon composite material according to claim 1 or 2, characterized in that: The diameter of the silicon nanoparticles is 0.5-5 nm. Preferably, the content of silicon in the silicon-carbon composite material is 5-80 wt.%.

6. The silicon-carbon composite material according to claim 1, characterized in that: It also includes a heteroatom X located in the pores of the C / C composite porous material, wherein the heteroatom X includes at least one of B, N, P, O and S, and the heteroatom X forms a Si-X chemical bond with the silicon atom in the silicon nanoparticles and separates and wraps the silicon nanoparticles; Preferably, the heteroatom content in the silicon-carbon composite material is 0 to 10 wt.%.

7. The silicon-carbon composite material according to claim 1, characterized in that: The silicon-carbon composite material particles have a coating layer on their surfaces; preferably, the material of the surface coating layer is selected from one or more of solid electrolytes, conductive polymers, carbonaceous materials, metals, alloys, metal oxides, metal halides, metal sulfides, metal phosphates, borates, sulfates, nitrates and polymetallic oxygen salts.

8. The silicon-carbon composite material according to claim 7, characterized in that: The surface of the silicon-carbon composite material particles has a coating layer with a grid structure. Preferably, the material of the coating layer includes at least one of carbon nanotubes, graphene, carbon black or carbon fiber.

9. The silicon-carbon composite material according to claim 1, characterized in that: The specific surface area of ​​the silicon-carbon composite material is 0.1 to 50 m 2 / g, pore volume is 0.01~0.5cm 3 / g; Preferably, the specific surface area of ​​the silicon-carbon composite material is 0.1 to 10 m 2 / g, pore volume is 0.01~0.1cm 3 / g; And / or, the true density of the silicon-carbon composite material is 1.3-2.0 g / cm 3 , closed pore volume is 0.01~0.25cm 3 / g.

10. A method for preparing the silicon-carbon composite material according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step S1, providing a C / C composite porous material, wherein the C / C composite porous material comprises a first carbon material and a second carbon material; the first carbon material is a porous carbon matrix, and the second carbon material runs through the C / C composite porous material; Step S2, contacting the silicon-containing precursor with the C / C composite porous material, performing chemical vapor deposition, so that silicon nanoparticles are distributed in the pores and on the surface of the C / C composite porous material, to obtain the silicon-carbon composite material; Wherein, the C / C composite porous material, the first carbon material, the second carbon material and the silicon nanoparticles have the same meanings as in claims 1 to 9, respectively.

11. The preparation method according to claim 10, characterized in that: The method for preparing the C / C composite porous material is to introduce a second carbon material into at least one of the different preparation processes in the preparation process of the porous carbon material, wherein the preparation process includes a carbon precursor process, a carbon precursor pre-stabilization process, a carbonization process, a further pore-forming process and a finished carbon material process; Preferably, the first carbon material precursor and the second carbon material are mixed, and the mixture is sintered in an inert atmosphere or a mixed atmosphere of an inert gas and an oxygen-containing gas to obtain a C / C composite porous material; or, Sintering a first carbon material precursor in an inert atmosphere to obtain a first carbon material, then mixing the first carbon material with a second carbon material, and sintering the mixture to obtain a C / C composite porous material; Wherein, the first carbon material precursor includes at least one of a polymer precursor, a biomass precursor and a fossil carbon source.

12. The preparation method according to claim 10, characterized in that: In step S2, the temperature of the silicon-containing precursor in contact with the C / C composite porous material is 150-1000° C. and the time is 1-100 h; and / or, introducing a heteroatom-containing precursor when the silicon-containing precursor is in contact with the C / C composite porous material; wherein the silicon-containing precursor and the heteroatom-containing precursor are in contact with the C / C composite porous material at a temperature of 150 to 1000° C. for a time of 1 to 100 hours; and / or, the silicon-containing precursor comprises at least one of monosilane, disilane, trisilane, halosilane, polysilane, silole and its derivatives, and silanol and its derivatives; And / or, the heteroatom-containing precursor includes at least one of a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor, or a boron-containing precursor.

13. A negative electrode, characterized in that: The negative electrode comprises the silicon-carbon composite material according to any one of claims 1 to 9 or the silicon-carbon composite material obtained by the preparation method according to any one of claims 10 to 12.

14. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the silicon-carbon composite material according to any one of claims 1 to 9 or the silicon-carbon composite material obtained according to the preparation method according to any one of claims 10 to 12.

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