A silicon-carbon composite material, its preparation method and application

Abstract

The present invention discloses a silicon-carbon composite material, a preparation method thereof and an application thereof, relating to the technical field of preparation of lithium-ion battery materials. Among them, the larger pore volume and higher specific surface area of the mesoporous carbon, as well as the heteroatoms doped in the mesoporous carbon, improve the electronic conductivity of the material; and the nanosilicon deposited in the mesoporous carbon improves the specific capacity of the material, the metal improves the electronic conductivity of the material, and the direct contact between the metal and the nanosilicon helps to form a stable solid electrolyte interface film and reduce side reactions, and reduces the probability of the nanosilicon being separated from the conductive network due to volume change during charge and discharge, and reduces the interfacial impedance; the amorphous carbon in the first shell layer isolates the nanosilicon from the external environment and reduces gas generation; the fast ion conductor outer shell helps to accelerate the migration of lithium ions in the electrode material during charge and discharge, and improves the rate performance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery material preparation, and particularly relates to a silicon-carbon composite material, a preparation method thereof and an application thereof. Background Art

[0002] As a silicon-based anode material, silicon-carbon materials are applied to high energy density lithium ion batteries due to their advantages such as high specific capacity (1800 - 2200 mAh / g), high first efficiency (90% - 92%), low expansion and good cycle performance.

[0003] Silicon-carbon materials are composed of porous carbon and nano-silicon deposited in the pores. However, due to the poor electronic conductivity of the porous carbon itself and the poor contact between the porous carbon and the nano-silicon, the interface impedance is large, resulting in low electronic conductivity and fast charging performance of the silicon-carbon materials.

[0004] In the prior art, attempts have been made to improve the power performance of silicon-carbon materials through doping, coating and other measures, but the effects are not obvious. Summary of the Invention

[0005] The main object of the present invention is to propose a silicon-carbon composite material, a preparation method thereof and an application thereof, aiming to solve the problem of low electronic conductivity and fast charging performance of silicon-carbon materials in the prior art.

[0006] To achieve the above object, the present invention proposes a silicon-carbon composite material, which is characterized in that it includes a main material, and a first shell layer and an outer shell that are sequentially covered on the surface of the main material;

[0007] Wherein, the main material includes mesoporous carbon, and heteroatoms, nano-silicon and metal are doped in the mesoporous carbon;

[0008] The first shell layer includes amorphous carbon; the outer shell includes a fast ion conductor.

[0009] In an embodiment, the heteroatom includes any one of nitrogen atoms and sulfur atoms; and / or,

[0010] The metal includes any one of magnesium, zinc and sodium; and / or,

[0011] The fast ion conductor includes LiAlSiO 4 、LiNbO 3 、Li 7 La 3 Zr 2 O 12 、Li 0.5 La 0.5 TiO 3 、Li 1.4 Al 0.4 Ti 1.6(PO 4 ) 3 Any one of the following.

[0012] In one embodiment, in the silicon-carbon composite material, the mass ratio of silicon, carbon, metal, heteroatom, and fast ion conductor is (40 - 45):(40 - 45):(1 - 2.5):(1 - 2.5):(8 - 15).

[0013] The present invention also provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0014] S10. Obtain mesoporous carbon doped with heteroatoms, transfer it to a fluidized bed, and under an inert atmosphere, introduce silane gas and metal gas for co-deposition to deposit nanosilicon and metal in the pores of the mesoporous carbon; then introduce a carbon source gas for carbon deposition to obtain a silicon-carbon precursor material;

[0015] S20. Perform fast ion conductor cyclic deposition on the silicon-carbon precursor material to obtain the silicon-carbon composite material.

[0016] In one embodiment, in step S10, the obtaining of mesoporous carbon doped with heteroatoms comprises the following steps:

[0017] Disperse a carbon source, a hard template agent, and a heteroatom compound in an organic solvent, then perform a hydrothermal synthesis reaction, sintering, and cleaning to obtain mesoporous carbon doped with heteroatoms.

[0018] In one embodiment, the mass ratio of the carbon source, the hard template agent, the heteroatom compound, and the organic solvent is 100:(1 - 10):(1 - 5):(500 - 1500); and / or,

[0019] The carbon source includes aliphatic polyurethane acrylate; and / or,

[0020] The hard template agent includes at least one of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, and the particle size of the hard template agent is 100 - 500 nm; and / or,

[0021] The heteroatom compound includes at least one of dopamine, pyrrole, thiophene, urea, and melamine; and / or,

[0022] The organic solvent includes at least one of xylene, acetone, ethyl acetate, and benzene; and / or,

[0023] The temperature of the hydrothermal synthesis reaction is 100 - 200 °C; and / or,

[0024] The pressure of the hydrothermal synthesis reaction is 1 - 5 MPa; and / or,

[0025] The time of the hydrothermal synthesis reaction is 1 to 6 h; and / or,

[0026] The temperature of the sintering is 600 to 1000 °C; and / or,

[0027] The time of the sintering is 1 to 6 h; and / or,

[0028] The cleaning includes cleaning with hydrochloric acid, and the molar concentration of the hydrochloric acid is 1 to 5 mol / L.

[0029] In one embodiment, in step S10:

[0030] The silane gas includes at least one of silane, trichlorosilane, dichlorosilane, monochlorosilane, disilane, dimethylsilane; and / or,

[0031] The metal gas includes the metal gas generated by heating metal magnesium, metal zinc or metal sodium to 1000 °C; and / or,

[0032] The volume ratio of the silane gas to the metal gas is 10:(1 to 3); and / or,

[0033] The total gas flow rate of the co-deposition is 10 to 100 mL / min; and / or,

[0034] The temperature of the co-deposition is 500 to 800 °C; and / or,

[0035] The time of the co-deposition is 60 to 600 min; and / or,

[0036] The carbon source gas includes at least one of methane, ethane, ethylene, acetylene, propyne; and / or,

[0037] The gas flow rate of the carbon deposition is 100 to 500 mL / min; and / or,

[0038] The temperature of the carbon deposition is 800 to 1100 °C; and / or,

[0039] The time of the carbon deposition is 30 to 300 min.

[0040] In one embodiment, in step S30:

[0041] The temperature of the fast ion conductor cyclic deposition is 200 to 250 °C; and / or,

[0042] The number of cycles of the fast ion conductor cyclic deposition is 50 to 150 times; and / or,

[0043] The fast ion conductor includes LiAlSiO 4 、LiNbO 3 、Li7 La 3 Zr 2 O 12 、Li 0.5 La 0.5 TiO 3 、Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 Any one of the above.

[0044] The present invention also provides an application, which uses the aforementioned silicon-carbon composite material or the silicon-carbon composite material prepared by the aforementioned preparation method of the silicon-carbon composite material in a lithium-ion battery.

[0045] The present invention provides a silicon-carbon composite material, a preparation method thereof, and an application. Mesoporous carbon has a large pore volume and a high specific surface area. Its elastic structure buffers the volume expansion of nanosilicon during charge and discharge, and at the same time provides a good electron transport path; the heteroatoms doped in the mesoporous carbon enhance the electron transport efficiency in the material, thereby improving the electronic conductivity of the material; the deposited nanosilicon in the mesoporous carbon increases the specific capacity of the material, and the metal improves the electronic conductivity of the material. Moreover, the direct contact between the metal and the nanosilicon enhances the electron and ion transport at the interface on the one hand, helps to form a stable solid electrolyte interface film and reduce side reactions, and on the other hand reduces the probability of the separation of the nanosilicon from the conductive network due to volume changes during charge and discharge, reducing the interface impedance; in addition, the amorphous carbon in the first shell isolates the nanosilicon from the external environment, reduces gas generation and improves safety; the fast ion conductor shell helps to accelerate the migration of lithium ions in the electrode material during charge and discharge, reduces the internal resistance of the material, and improves the charge and discharge rate and power performance of the material. Description of the Drawings

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0047] Figure 1 It is a scanning electron microscope image of the silicon-carbon composite material in Embodiment 4 provided by the present invention.

[0048] The realization, functional characteristics, and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the drawings. Detailed Embodiments

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0050] As a silicon-based anode material, silicon-carbon materials are applied to high-energy-density lithium-ion batteries due to their high specific capacity (1800 - 2200 mAh / g), high first efficiency (90% - 92%), low expansion, and good cycling performance.

[0051] Silicon-carbon materials are composed of porous carbon and nano-silicon deposited in the pores. When the contact between the nano-silicon and the conductive carbon material is insufficient, it will lead to the obstruction of the electron transport path and increase the interfacial impedance; during the charge and discharge process, the silicon will undergo volume changes, which may also cause the material to crack or separate from the conductive network, increasing the interfacial impedance. A large interfacial impedance will affect the thickness and stability of the solid electrolyte interface (SEI) film, limit the rapid insertion and extraction of lithium ions, and thus affect the fast charging performance.

[0052] In the prior art, attempts have been made to improve the power performance of silicon-carbon materials through measures such as doping and coating, but the effects are not obvious.

[0053] In view of this, the present invention provides a silicon-carbon composite material, which is characterized in that it includes a main material, and a first shell layer and an outer shell that are sequentially covered on the surface of the main material;

[0054] Among them, the main material includes mesoporous carbon, and heteroatoms, nano-silicon, and metal are doped in the mesoporous carbon;

[0055] The first shell layer includes amorphous carbon; the outer shell includes a fast ion conductor.

[0056] In the technical solution of the present invention, the mesoporous carbon has a large pore volume and a high specific surface area. Its elastic structure buffers the volume expansion of nano-silicon during charge and discharge, and at the same time provides a good electron transport path; the heteroatoms doped in the mesoporous carbon form local defects, enhancing the electron transport efficiency in the material, thereby improving the electronic conductivity of the material; the nano-silicon deposited in the mesoporous carbon increases the specific capacity of the material, and the metal improves the electronic conductivity of the material. The direct contact between the metal and nano-silicon enhances the electron and ion transport at the interface on the one hand, contributing to the formation of a stable solid electrolyte interface film and reducing side reactions, and on the other hand reducing the probability of the separation of nano-silicon from the conductive network due to volume changes during charge and discharge, reducing the interface impedance; in addition, the amorphous carbon in the first shell isolates the nano-silicon from the external environment, reducing gas generation and improving safety; the fast ion conductor shell helps to accelerate the migration of lithium ions in the electrode material during charge and discharge, reducing the internal resistance of the material, and improving the charge and discharge rate and power performance of the material.

[0057] The pore volume of the mesoporous carbon is 0.8 - 1.1 cm 2 / g, and the specific surface area is 1000 - 1500 m 2 / g.

[0058] In some embodiments of the present invention, the heteroatoms include any one of nitrogen atoms and sulfur atoms. Selecting the above heteroatoms can introduce point defects or line defects in the mesoporous carbon. These defects can serve as sources of additional electrons or holes, or act as electron / hole transport channels, thereby improving the conductivity of the material.

[0059] In some embodiments of the present invention, the metal includes any one of magnesium, zinc, and sodium. The reason for selecting the above metals is that they have low costs and are easy to obtain.

[0060] In some embodiments of the present invention, the fast ion conductor includes any one of LiAlSiO 4 , LiNbO 3 , Li 7 La 3 Zr 2 O 12 , Li 0.5 La 0.5 TiO 3 , Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 The above fast ion conductors have high lithium ion conductivity, ensuring the rapid transport of lithium ions during charge and discharge, thereby improving the power density and response speed of the material.

[0061] In some embodiments of the present invention, in the silicon-carbon composite material, the mass ratio of silicon, carbon, metal, heteroatom, and fast ion conductor is (40-45):(40-45):(1-2.5):(1-2.5):(8-15). The mass ratio can be 40:40:2.5:2.5:15 or 45:45:1:1:8. Such a mass ratio within a suitable range can not only ensure that the material has a high specific capacity and electron / ion conductivity, but also maintain good structural stability and cycling performance.

[0062] The present invention also provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0063] S10. Obtain mesoporous carbon doped with heteroatoms, transfer it to a fluidized bed, and under an inert atmosphere, introduce silane gas and metal gas for co-deposition, so that nanosilicon and metal are deposited in the pores of the mesoporous carbon; then introduce a carbon source gas for carbon deposition to obtain a silicon-carbon precursor material;

[0064] S20. Perform fast ion conductor cyclic deposition on the silicon-carbon precursor material to obtain the silicon-carbon composite material.

[0065] In the technical solution of the present invention, the co-deposition of nanosilicon and metal increases the contact area between nanosilicon and metal, forming an effective electron transport path, and the contact area means more active sites, which is conducive to the formation of a more stable SEI film and reduces the occurrence of side reactions; nanosilicon will undergo a large volume change during charge and discharge, while the mesoporous carbon near the nanosilicon can help relieve the volume expansion of silicon, thereby improving the mechanical stability and cycling life of the final material, and the metal itself can store lithium ions and cooperate with nanosilicon to improve the specific capacity and electron conductivity of the material; carbon deposition on the surface of the mesoporous carbon composite material, on the one hand, carbon deposition can construct a continuous electron conductive network, promote the transport of electrons in the electrode material, and improve the overall conductive performance of the material, on the other hand, the carbon layer can also absorb and buffer the volume expansion and contraction of nanosilicon during charge and discharge, avoiding the fragmentation of silicon particles and their detachment from the electrode. In addition, the nanosilicon deposited in the mesoporous carbon is highly active and will explode when encountering air or oxygen. Depositing amorphous carbon on its surface for surface passivation is convenient for improving safety performance; fast ion conductor cyclic deposition can deposit a fast ion conductor with a higher density and better uniformity on the surface of the silicon-carbon precursor material, thereby improving the ion conductivity and power performance of the material.

[0066] In the technical solution of the present invention, through the co-deposition of silane gas and metal gas and the deposition of a carbon source gas, nanosilicon and metal are deposited in the mesoporous carbon to improve the electron conductivity of the material, improve the interfacial impedance in the inner core mesopores, and deposit amorphous carbon on its surface, reducing the specific surface area and the defects of the mesoporous carbon, and improving the first efficiency and its electron conductivity.

[0067] In some embodiments of the present invention, in step S10, the obtaining of the heteroatom-doped mesoporous carbon includes the following steps:

[0068] After dispersing a carbon source, a hard template agent, and a heteroatom compound in an organic solvent, a hydrothermal synthesis reaction is carried out, followed by sintering and washing to obtain the heteroatom-doped mesoporous carbon.

[0069] In the technical solution of the present invention, under hydrothermal conditions, the carbon source undergoes polymerization and carbonization, the hard template agent guides the carbon source to form a mesoporous structure, and at the same time, the heteroatom compound decomposes and is incorporated into the carbon skeleton. This step improves the electronic conductivity of the material and the pore volume of the carbon material, and helps to reduce the expansion of nanosilicon during charge and discharge; sintering is carried out in an inert atmosphere to remove the residual hard template agent, stabilize the material structure, and improve the doping efficiency of heteroatoms; washing can further remove the residues of the hard template agent and by-products.

[0070] In some embodiments of the present invention, the mass ratio of the carbon source, the hard template agent, the heteroatom compound, and the organic solvent is 100:(1-10):(1-5):(500-1500). The mass ratio of the carbon source, the hard template agent, the heteroatom compound, and the organic solvent can be 100:10:5:1500, 100:5:3:1000, or 100:1:1:500. The mass ratio within a suitable range can ensure the formation of a mesoporous structure and a high doping amount of heteroatoms, while maintaining the basic structure of the carbon material without being damaged.

[0071] In some embodiments of the present invention, the carbon source includes aliphatic polyurethane acrylate. The aliphatic polyurethane acrylate is a polymer that contains both the urethane bond of polyurethane and the carbon-carbon double bond of acrylate in its molecule. Therefore, they can be crosslinked or cured through a free radical polymerization reaction. As a carbon source, aliphatic polyurethane acrylate has good mechanical properties and thermal stability and can be crosslinked through a free radical polymerization reaction to form a relatively uniform pore structure.

[0072] In some embodiments of the present invention, the hard template agent includes at least one of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, and the particle size of the hard template agent is 100-500 nm. That is, the hard template agent can be any one of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, or two or more of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, all within the protection scope of the present invention. The particle size of the hard template agent can be 100 nm, 300 nm, or 500 nm, and its particle size within a suitable range can form pores with better mechanical stability.

[0073] In some embodiments of the present invention, the heteroatom compound includes at least one of dopamine, pyrrole, thiophene, urea, and melamine. That is, the heteroatom compound can be any one of dopamine, pyrrole, thiophene, urea, and melamine, or two or more of dopamine, pyrrole, thiophene, urea, and melamine, all of which are within the protection scope of the present invention. The above heteroatom compound can effectively incorporate nitrogen elements into the carbon material and improve the electronic conductivity of the carbon material.

[0074] In some embodiments of the present invention, the organic solvent includes at least one of xylene, acetone, ethyl acetate, and benzene. That is, the organic solvent can be any one of xylene, acetone, ethyl acetate, and benzene, or two or more of xylene, acetone, ethyl acetate, and benzene, all of which are within the protection scope of the present invention. The above organic solvent has good solubility and stability, can ensure the efficient progress of the reaction, and is not prone to side reactions.

[0075] In some embodiments of the present invention, the temperature of the hydrothermal synthesis reaction is 100 - 200 °C. The temperature of the hydrothermal synthesis reaction can be 100 °C, 140 °C, or 200 °C. When the temperature is within a suitable range, it can ensure the preparation of heteroatom-doped mesoporous carbon with high quality and purity.

[0076] In some embodiments of the present invention, the pressure of the hydrothermal synthesis reaction is 1 - 5 MPa. The pressure of the hydrothermal synthesis reaction can be 1 MPa, 3 MPa, or 5 MPa. When the pressure is within a suitable range, it can ensure the preparation of heteroatom-doped mesoporous carbon with high quality and purity.

[0077] In some embodiments of the present invention, the time of the hydrothermal synthesis reaction is 1 - 6 h. The time of the hydrothermal synthesis reaction can be 1 h, 3 h, or 6 h. When the time is within a suitable range, it can ensure the preparation of heteroatom-doped mesoporous carbon with high quality and purity, and help control the pore size in the mesoporous carbon, and there is sufficient time to remove the hard template agent.

[0078] In some embodiments of the present invention, the temperature of the sintering is 600 - 1000 °C. The temperature of the sintering can be 600 °C, 800 °C, or 1000 °C. When the temperature is within a suitable range, it can ensure the promotion of carbonization, the removal of residual hard template agent, and the enhancement of the density of the material, thereby leaving a more stable mesoporous structure.

[0079] In some embodiments of the present invention, the time of the sintering is 1 - 6 h. The time of the sintering can be 1 h, 3 h, or 6 h. When the time is within a suitable range, it can ensure sufficient time to remove the hard template agent and enhance the mechanical strength and mesoporous stability of the material.

[0080] In some embodiments of the present invention, the cleaning includes cleaning with hydrochloric acid, and the molar concentration of the hydrochloric acid is 1 to 5 mol / L. The molar concentration of the hydrochloric acid can be 1 mol / L, 3 mol / L, or 5 mol / L. A molar concentration within a suitable range can ensure effective dissolution of the hard template agent, thereby releasing the mesoporous structure.

[0081] In some embodiments of the present invention, the silane gas includes at least one of silane, trichlorosilane, dichlorosilane, monochlorosilane, disilane, and dimethylsilane. After the above silane gas decomposes at high temperature, nano-silicon can be deposited in the pores of the heteroatom-doped mesoporous carbon more efficiently.

[0082] In some embodiments of the present invention, the metal gas includes the metal gas generated by heating metallic magnesium, metallic zinc, or metallic sodium to 1000 °C. The metal gas is metal vapor and is composed of metal atoms or small atom clusters. Selecting the above metal gas has a low decomposition temperature, low energy consumption, and relatively low cost.

[0083] In some embodiments of the present invention, the volume ratio of the silane gas to the metal gas is 10:(1 - 3). The volume ratio of the silane gas to the metal gas can be 10:3, 10:2, or 10:1. A volume ratio within a suitable range can improve the electronic conductivity of the mesoporous carbon and deposit nano-silicon in the pores, thereby increasing the specific capacity.

[0084] In some embodiments of the present invention, the total flow rate of the co-deposited gas is 10 to 100 mL / min. The total flow rate of the co-deposited gas can be 10 mL / min, 60 mL / min, or 100 mL / min. A total gas flow rate within a suitable range can ensure a relatively high deposition efficiency and a relatively uniform deposition layer.

[0085] In some embodiments of the present invention, the co-deposition temperature is 500 to 800 °C. The co-deposition temperature can be 500 °C, 700 °C, or 800 °C. A temperature within a suitable range can ensure material decomposition while improving the deposition efficiency.

[0086] In some embodiments of the present invention, the co-deposition time is 60 to 600 min. The co-deposition time can be 60 min, 400 min, or 600 min. A time within a suitable range can ensure a relatively uniform deposition layer.

[0087] In some embodiments of the present invention, the carbon source gas includes at least one of methane, ethane, ethylene, acetylene, and propyne. That is, the carbon source gas can be any one of methane, ethane, ethylene, acetylene, and propyne, or two or more of methane, ethane, ethylene, acetylene, and propyne, all of which are within the protection scope of the present invention. The above carbon source gas can efficiently decompose and deposit a carbon layer.

[0088] In some embodiments of the present invention, the gas flow rate of carbon deposition is 100 - 500 mL / min. The gas flow rate of carbon deposition can be 100 mL / min, 300 mL / min, or 500 mL / min. When the gas flow rate is within a suitable range, the efficiency of depositing the carbon layer can be ensured to be relatively high.

[0089] In some embodiments of the present invention, the temperature of carbon deposition is 800 - 1100 °C. The temperature of carbon deposition can be 800 °C, 950 °C, or 1100 °C. When the temperature is within a suitable range, while ensuring the decomposition of the carbon source, the density of the deposited carbon layer can be relatively high.

[0090] In some embodiments of the present invention, the time of carbon deposition is 30 - 300 min. The time of carbon deposition can be 30 min, 250 min, or 300 min. When the time is within a suitable range, the thickness of the deposited carbon layer can be appropriate and the carbon layer can be relatively uniform.

[0091] In some embodiments of the present invention, in step S30: the temperature of cyclic deposition of the fast ion conductor is 200 - 250 °C. The temperature of cyclic deposition of the fast ion conductor can be 200 °C, 220 °C, or 250 °C. When the temperature is within a suitable range, it can ensure that the uniformity, density, and crystallinity of the fast ion conductor shell are relatively good, and the interfacial bonding with the substrate is relatively good, reducing the interfacial impedance.

[0092] In some embodiments of the present invention, in step S30: the number of cycles of cyclic deposition of the fast ion conductor is 50 - 150 times. The number of cycles of cyclic deposition of the fast ion conductor can be 50 times, 100 times, or 150 times. When the number of cycles is within a suitable range, it can ensure that the uniformity and density of the shell are relatively good, contribute to the formation of a stable and continuous SEI interface, and balance the ionic conductivity and nano - silicon activity of the material.

[0093] In some embodiments of the present invention, in step S30: the fast ion conductor includes LiAlSiO 4 、LiNbO 3 、Li 7 La 3 Zr 2 O 12 、Li 0.5 La0.5 TiO 3 、 Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 Any one of the above. Selecting the above-mentioned fast ion conductor can ensure a relatively fast migration speed of lithium ions, contribute to the formation of a relatively stable SEI film, and thus improve the power density and charging speed of the battery.

[0094] The present invention also provides an application, using the aforementioned silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method of the aforementioned silicon-carbon composite material in a lithium-ion battery. The silicon-carbon composite material has all the above beneficial effects, which will not be elaborated one by one here.

[0095] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0096] Example 1

[0097] A silicon-carbon composite material includes a main material and a shell. Among them, the main material includes mesoporous carbon, heteroatoms doped in the mesoporous carbon, nano-silicon, and metallic lithium; and a first shell layer and a shell that successively cover the surface of the main material; the first shell layer includes amorphous carbon; the shell includes a fast ion conductor.

[0098] The mass ratio of silicon, carbon, metallic lithium, heteroatoms, and fast ion conductor in the silicon-carbon composite material is 43:43:2:2:10;.

[0099] Example 2

[0100] Example 2 is similar to Example 1, the difference is that:

[0101] The mass ratio of silicon, carbon, metallic lithium, heteroatoms, and fast ion conductor in the silicon-carbon composite material is 45:40:1:1:8;.

[0102] Example 3

[0103] Example 3 is similar to Example 1, the difference is that:

[0104] The mass ratio of silicon, carbon, metallic lithium, heteroatoms, and fast ion conductor in the silicon-carbon composite material is 40:45:2.5:2.5:15.

[0105] Example 4

[0106] A preparation method of a silicon-carbon composite material includes the following steps:

[0107] S10. Add 100 g of aliphatic polyurethane acrylate to 1000 g of xylene organic solvent and disperse evenly. Then add 5 g of silica microspheres (particle size of 500 nm) and 3 g of dopamine, and disperse evenly by ultrasonic treatment. Then transfer to a high-pressure reactor, react at a temperature of 150 °C and a pressure of 3 MPa for 3 h, filter, and sinter the obtained filter residue at a temperature of 800 °C for 3 h. Then wash it 3 times with 3 mol / L hydrochloric acid to obtain heteroatom-doped mesoporous carbon;

[0108] Transfer the heteroatom-doped mesoporous carbon to a fluidized bed. First, introduce argon inert gas to exhaust the air in the tube, heat to 650 °C, and then simultaneously introduce silane gas and magnesium metal gas (the volume ratio of silane gas to magnesium metal gas is 10:2). Introduce at a gas flow rate of 50 mL / min for 300 min, then raise the temperature to 950 °C, introduce ethylene gas at a gas flow rate of 300 mL / min for 150 min, and then cool to room temperature under an argon inert atmosphere to obtain a silicon-carbon precursor material;

[0109] S20. Place the silicon-carbon precursor material powder in the reaction chamber, evacuate the chamber to 0.1 torr, raise the temperature to 220 °C, and use LiAlSiO 4 Deposit according to the following procedure: (1) Introduce LiAlSiO 4 for 0.3 s; (2) Purge with nitrogen for 60 s; (3) Introduce the oxygen source for 5 s; (4) Purge with nitrogen for 5 s; (5) Introduce water for 0.03 s; (6) Purge with nitrogen for 50 s; (7) Start cycling from step (1) for 100 cycles for cyclic deposition, so that a LiAlSiO 4 deposition layer with a uniform thickness is formed layer by layer on the surface of the silicon-carbon precursor material. After completing the cyclic deposition, cool to room temperature to obtain a silicon-carbon composite material.

[0110] Example 5

[0111] A method for preparing a silicon-carbon composite material, comprising the following steps:

[0112] S10. Add 100 g of aliphatic polyurethane acrylate to 500 g of acetone organic solvent and disperse evenly. Then add 1 g of calcium carbonate microspheres (particle size of 500 nm) and 1 g of pyrrole, and disperse evenly by ultrasonic treatment. Then transfer to a high-pressure reactor, react at a temperature of 100 °C and a pressure of 5 MPa for 6 h, filter, and sinter the obtained filter residue at a temperature of 600 °C for 6 h. Then wash it 3 times with 1 mol / L hydrochloric acid to obtain heteroatom-doped mesoporous carbon;

[0113] Transfer the heteroatom-doped mesoporous carbon to a fluidized bed. First, introduce argon inert gas to expel the air in the tube, heat it to 500 °C, and then simultaneously introduce trichlorosilane gas and metallic zinc gas (the volume ratio of trichlorosilane gas to metallic zinc gas is 10:1), introduce it at a flow rate of 10 mL / min for 600 min, then raise the temperature to 800 °C, introduce acetylene gas at a gas flow rate of 100 mL / min for 300 min, and then cool it to room temperature under an argon inert atmosphere to obtain a silicon-carbon precursor material;

[0114] S20. Place the silicon-carbon precursor material powder in the reaction chamber, evacuate the chamber to 0.1 torr, raise the temperature to 200 °C, and add LiNbO 3 Deposit according to the following procedure: (1) Introduce LiNbO 3 for 0.3 s; (2) Purge with nitrogen for 60 s; (3) Introduce the oxygen source for 5 s; (4) Purge with nitrogen for 5 s; (5) Introduce water for 0.03 s; (6) Purge with nitrogen for 50 s; (7) Cycle 50 times starting from step (1) for cyclic deposition, so that a LiNbO 3 deposition layer with a uniform thickness is formed layer by layer on the surface of the silicon-carbon precursor material. After completing the cyclic deposition, cool it to room temperature to obtain a silicon-carbon composite material.

[0115] Example 6

[0116] A preparation method of a silicon-carbon composite material includes the following steps:

[0117] S10. Add 100 g of aliphatic polyurethane acrylate to 1500 g of ethyl acetate organic solvent and disperse it evenly, then add 10 g of zinc oxide microspheres (particle size of 500 nm) and 5 g of urea, ultrasonically disperse it evenly, then transfer it to a high-pressure reactor, react at a temperature of 200 °C and a pressure of 1 MPa for 1 h, filter, sinter the obtained filter residue at a temperature of 1000 °C for 1 h, and then wash it 3 times with 5 mol / L hydrochloric acid to obtain heteroatom-doped mesoporous carbon;

[0118] Transfer the heteroatom-doped mesoporous carbon to a fluidized bed. First, introduce argon inert gas to expel the air in the tube, heat it to 800 °C, and then simultaneously introduce dichlorosilane gas and metallic sodium gas (the volume ratio of dichlorosilane gas to metallic sodium gas is 10:3), introduce it at a gas flow rate of 100 mL / min for 60 min, then raise the temperature to 1100 °C, introduce methane gas at a gas flow rate of 500 mL / min for 30 min, and then cool it to room temperature under an argon inert atmosphere to obtain a silicon-carbon precursor material;

[0119] S20. Place the silicon-carbon precursor material powder in the reaction chamber, evacuate the chamber to 0.1 torr, raise the temperature to 250 °C, and add Li 7 La3 Zr 2 O 12 Deposition is carried out according to the following procedure: (1) Introduce Li 7 La 3 Zr 2 O 12 for 0.3 seconds; (2) Purge with nitrogen for 60 seconds; (3) Introduce an oxygen source for 5 seconds; (4) Purge with nitrogen for 5 seconds; (5) Introduce water for 0.03 seconds; (6) Purge with nitrogen for 50 seconds; (7) Start cycling from step (1) for 150 cycles for cyclic deposition, so that a Li 7 La 3 Zr 2 O 12 deposition layer with a uniform thickness is formed layer by layer on the surface of the silicon-carbon precursor material. After completing the cyclic deposition, it is cooled to room temperature to obtain a silicon-carbon composite material.

[0120] Comparative Example 1

[0121] Compared with Example 1, Comparative Example 1 is the same as Example 1 except that step S20 is not carried out.

[0122] Comparative Example 2

[0123] Compared with Example 1, Comparative Example 2 is the same as Example 1 except that metal magnesium gas is not introduced in step S10.

[0124] Performance test

[0125] The silicon-carbon composite material prepared in Example 4 was observed by scanning electron microscopy.

[0126] It can be seen from Figure 1 that the silicon-carbon composite material presents a granular structure, with a small amount of precipitate on the surface, the particle size is between 5 and 10 μm, and the size distribution is uniform.

[0127] Physical and chemical property test:

[0128] According to the method in the national standard GB / T 38823-2020 "Silicon Carbide", the specific surface area and tapped density of the silicon-carbon composite materials obtained in Examples 4 to 6 and Comparative Examples 1 to 2 were respectively tested, and the resistivity of the silicon-carbon composite materials was tested using a powder resistance tester; and the gas production of its powder material (45 °C, 48 h) was tested, and the results are shown in Table 1 below.

[0129] Table 1 Physical and chemical properties of the silicon-carbon composite materials in Examples 4 to 6 and Comparative Examples 1 to 2

[0130]

[0131] As can be seen from Table 1, the specific surface area and tap density of the silicon-carbon composite materials in Examples 4 to 6 are higher than those in Comparative Examples 1 and 2, while the resistivity and gas generation are lower than those in Comparative Examples 1 and 2. This indicates that the silicon-carbon composite materials prepared by the present invention have a high specific surface area, a high tap density, a low resistivity, and a low gas generation volume.

[0132] Button cell test:

[0133] The silicon-carbon composite materials obtained in Examples 4 to 6 and Comparative Examples 1 and 2 were used as the active materials of the battery negative electrode sheets, and 5 button cells were respectively prepared and assembled; among them, the specific preparation process of each button cell was as follows:

[0134] Preparation of battery negative electrode sheets: In the silicon-carbon composite materials corresponding to Examples 4 to 6 and Comparative Examples 1 and 2 (as the active materials of the battery negative electrode sheets), a binder, a conductive agent, and a solvent were respectively added, stirred to make a slurry, coated on a copper foil, and dried and rolled to obtain each battery negative electrode sheet; among them, the binder was LA132 binder, the conductive agent was SP (conductive carbon black), and the solvent was NMP, and the ratio was: silicon-carbon composite material: SP: LA132: NMP = 95 g: 1 g: 4 g: 220 mL; Preparation of button cells: The electrolyte was LiPF 6 solution, where the concentration of LiPF 6 was 1 mol / L, and the solvent used was a mixed solution of ethylene carbonate and diethyl carbonate with a weight ratio of 1:1; a metal lithium sheet was used as the counter electrode, and the separator was a polypropylene (PP) membrane. The simulation battery was assembled in a glove box filled with argon gas, and the electrochemical performance was tested on a Wuhan Blue Electric CT2001A battery tester. The test conditions were: the charge-discharge voltage range was 0.005 V to 2.0 V, and the charge-discharge rate was 0.1 C; and its rate performance (1 C / 0.1 C) was tested. A full-charge swelling test was also carried out: for the rolled button cell negative electrode sheet, the thickness D1 of the negative electrode sheet was measured, and then the negative electrode sheet of the button cell was dissected under a full charge to 100% SOC, and the thickness D2 of the negative electrode sheet was measured, and then the full-charge swelling rate = (D2 - D1) / D1 * 100% was calculated. The results are shown in Table 2 below.

[0135] Table 2 Performance characterization of button cells corresponding to Examples 4 to 6 and Comparative Examples 1 and 2

[0136]

[0137] As can be seen from Table 2 above, the button cells fabricated using the silicon-carbon composite materials provided in Examples 4 to 6 of the present application are significantly superior to Comparative Examples 1 and 2 in terms of the initial discharge specific capacity and the initial efficiency. The reason may be that: by using magnesium doping to form magnesium silicate in the materials of the present application, the structural stability of the materials is enhanced and the irreversible capacity is reduced, and a fast ion conductor of lithium is coated on the surface thereof, thereby enhancing the ionic conductivity of the materials and reducing defects, and improving the rate performance and the initial efficiency.

[0138] Soft-pack battery test:

[0139] The silicon-carbon composite materials obtained in Examples 4 to 6 and Comparative Examples 1 and 2 were respectively doped with 90% artificial graphite as the negative electrode material (i.e., the negative electrode sheet), and a ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 was used as the positive electrode material, electrolyte and separator to assemble a 5 Ah soft-pack battery; wherein, the separator of the soft-pack battery was Celgard 2400, and the electrolyte was LiPF 6 solution, and the solvent of the LiPF 6 solution was a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF 6 was 1.3 mol / L. The following performance tests were carried out on each soft-pack battery:

[0140] Liquid absorption capacity test: A 1 mL burette was used to suck 1 mL of electrolyte, and a drop was added dropwise on the surface of the negative electrode sheet and timed until the electrolyte was completely absorbed, and the time t was recorded. The results are shown in Table 3 below;

[0141] Polar surface resistance test: A polar surface resistance tester was used to place the electrode sheet (100 cm 2 ) on the test bench and test its resistance under a pressure of 500 kg. The results are shown in Table 3 below;

[0142] Rate and cycle performance: Cycle performance tests and rate tests were carried out on each soft-pack battery; the test conditions for the cycle performance test were: the charge-discharge voltage range was 2.5 to 4.2 V, the temperature was 25 ± 3.0 °C, the charge-discharge rate was 1.0 C / 1.0 C, and the number of cycles was 500 times; the test conditions for the rate test were: the charge constant current ratio at different charge rates (0.5 C, 1 C, 2 C, and 3 C) was tested. The test results are shown in Table 4 below.

[0143] Table 3 Liquid absorption speed and polar surface resistance of the soft-pack batteries corresponding to Examples 4 to 6 and Comparative Examples 1 and 2

[0144] Liquid absorption rate (S) Polar surface resistance (Ω·cm) Example 4 87 11.23 Example 5 98 13.23 Example 6 75 9.25 Comparative Example 1 132 17.34 Comparative Example 2 113 14.25

[0145] As can be seen from Table 3 above, the liquid absorption and the electrode surface resistance of the silicon-carbon composite materials provided in Examples 4 to 6 of this application are significantly better than those of Comparative Examples 1 to 3. The reason is that the materials in Examples 4 to 6 have a high specific surface area to improve the liquid absorption capacity of the material and a low powder resistivity to reduce the electrode surface resistance.

[0146] Table 4 Rate and cycle performance of the coin cells corresponding to Examples 4 to 6 and Comparative Examples 1 to 2

[0147]

[0148] As can be seen from Table 4 above, the rate performance and cycle performance of the soft-pack lithium-ion batteries prepared with the silicon-carbon composite materials of Examples 4 to 6 of this application are better than those of Comparative Examples 1 to 2. The reason may mainly lie in that: the silicon-carbon composite materials provided in the examples of this application have a high powder conductivity and a low electrode surface resistance, which improve the rate performance of the materials, and their low expansion and high specific surface area improve the liquid retention performance and cycle performance of the materials.

[0149] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the patent protection scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that: It comprises a main body material, and a first shell layer and an outer shell sequentially covering the surface of the main body material; Wherein, the main material comprises mesoporous carbon, and the mesoporous carbon is doped with heteroatoms, nano-silicon and metal; The first shell layer comprises amorphous carbon; the outer shell comprises a fast ion conductor; The heteroatom includes any one of nitrogen atom and sulfur atom; the metal includes any one of magnesium, zinc and sodium; the fast ion conductor includes LiAlSiO4, LiNbO3, Li7La3Zr2O 12 , Li 0.5 La 0.5 TiO3、Li 1.4 Al 0.4 Ti 1.6 Any of (PO4)3; The silicon-carbon composite material is prepared by the following steps: S10, obtaining mesoporous carbon doped with heteroatoms, and transferring it to a fluidized bed, and introducing silane gas and metal gas for co-deposition under an inert atmosphere, so that nano-silicon and metal are deposited in the pores of the mesoporous carbon; then introducing carbon source gas for carbon deposition to obtain a silicon-carbon precursor material; the carbon source gas includes at least one of methane, ethane, ethylene, acetylene, and propyne; S20, subjecting the silicon-carbon precursor material to fast ion conductor cyclic deposition to obtain the silicon-carbon composite material; In step S10, the process of obtaining mesoporous carbon doped with heteroatoms includes the following steps: dispersing a carbon source, a hard template and a heteroatom compound in an organic solvent, performing a hydrothermal synthesis reaction, sintering, and washing to obtain mesoporous carbon doped with heteroatoms; wherein the carbon source includes aliphatic polyurethane acrylate; the hard template includes at least one of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, and the particle size of the hard template is 100~500nm; the heteroatom compound includes at least one of dopamine, pyrrole, thiophene, urea, and melamine.

2. The silicon-carbon composite material according to claim 1, characterized in that: In the silicon-carbon composite material, the mass ratio of silicon, carbon, metal, heteroatom and fast ion conductor is (40-45): (40-45): (1-2.5): (1-2.5): (8-15).

3. A method for preparing the silicon-carbon composite material according to any one of claims 1 to 2, characterized in that: The following steps are involved: S10, obtaining mesoporous carbon doped with heteroatoms, and transferring it to a fluidized bed, and introducing silane gas and metal gas for co-deposition under an inert atmosphere, so that nano-silicon and metal are deposited in the pores of the mesoporous carbon; and then introducing carbon source gas for carbon deposition to obtain a silicon-carbon precursor material; S20, subjecting the silicon-carbon precursor material to fast ion conductor cyclic deposition to obtain the silicon-carbon composite material.

4. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that: The mass ratio of the carbon source, the hard template, the heteroatom compound and the organic solvent is 100: (1-10): (1-5): (500-1500); and / or, The carbon source comprises aliphatic polyurethane acrylate; and / or, The hard template comprises at least one of silica microspheres, calcium carbonate microspheres, and zinc oxide microspheres, and the particle size of the hard template is 100-500 nm; and / or, The heteroatom compound includes at least one of dopamine, pyrrole, thiophene, urea and melamine; and / or, The organic solvent comprises at least one of xylene, acetone, ethyl acetate and benzene; and / or, The temperature of the hydrothermal synthesis reaction is 100-200° C.; and / or, The pressure of the hydrothermal synthesis reaction is 1-5 MPa; and / or, The hydrothermal synthesis reaction time is 1 to 6 hours; and / or, The sintering temperature is 600-1000° C.; and / or, The sintering time is 1 to 6 hours; and / or, The cleaning includes cleaning with hydrochloric acid, and the molar concentration of the hydrochloric acid is 1-5 mol / L.

5. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that: In step S10: The silane gas includes at least one of tetrahydrosilane, trichlorosilane, dichlorosilane, monochlorosilane, disilane and dimethylsilane; and / or, The metal gas includes metal gas generated by heating metal magnesium, metal zinc or metal sodium to 1000° C.; and / or, The volume ratio of the silane gas to the metal gas is 10:(1-3); and / or, The total gas flow rate of the co-deposition is 10-100 mL / min; and / or, The co-deposition temperature is 500-800° C.; and / or, The co-deposition time is 60 to 600 minutes; and / or, The carbon source gas includes at least one of methane, ethane, ethylene, acetylene and propyne; and / or, The gas flow rate of the carbon deposition is 100-500 mL / min; and / or, The temperature of the carbon deposition is 800-1100° C.; and / or, The carbon deposition time is 30 to 300 minutes.

6. The method for preparing the silicon-carbon composite material according to claim 3, characterized in that: In step S20: The temperature of the fast ion conductor cyclic deposition is 200-250° C.; and / or, The number of cycles of the fast ion conductor cyclic deposition is 50 to 150 times; and / or, Fast ion conductors include LiAlSiO4, LiNbO3, Li7La3Zr2O 12 , Li 0.5 La 0.5 TiO3、Li 1.4 Al 0.4 Ti 1.6 Any of (PO4)3.

7. An application of a silicon-carbon composite material, characterized in that: The silicon-carbon composite material as claimed in any one of claims 1 to 2 or the silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material as claimed in any one of claims 3 to 6 is used in a lithium-ion battery.

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