Silicon-carbon composite material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a silicon-carbon composite material and a preparation method thereof and a lithium ion battery, the silicon-carbon composite material comprises an inner core, the inner core comprises a composite carbon matrix and a silicon material formed in pores and the surface of the composite carbon matrix, the composite carbon matrix is formed by compounding first-phase carbon and second-phase carbon, the first phase carbon is a phenolic resin-based carbon material, and the second phase carbon is a fiber-type carbon material; the coating layer is formed on the surface of the inner core, and the coating layer is a carbon layer. The silicon-carbon composite material has the advantages of being high in structural strength and good in conductivity, volume expansion of the material can be relieved, the capacity retention ratio and the cycle performance of the material are improved, and the comprehensive performance is excellent.

Description

Technical Field

[0001] The present application belongs to the technical field of negative electrode materials for lithium-ion batteries, and specifically relates to a silicon-carbon composite material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Among the negative electrode materials of lithium-ion batteries, silicon is one of the most promising negative electrode materials besides graphite. Although silicon has a high theoretical capacity (about 4200mAh / g) and a low discharge potential (about 0.06Vvs.Li / Li + ), however, in practical applications, silicon anodes still face major challenges: silicon easily expands in volume during lithiation, leading to mechanical stress and electrode degradation; in addition, the instability of the solid electrolyte interface (SEI) during cycling will lead to continuous consumption of active materials and a continuous decrease in coulombic efficiency.

[0003] Although combining silicon and carbon to form a silicon-carbon composite material can improve electronic / ionic conductivity and mechanical properties to a certain extent, and the formation of a coating layer can also alleviate the volume expansion of the material, there are still problems such as low matrix strength, easy breakage of particles during the roll-pressing process of preparing negative electrode sheets, and further improvement of material expansion and cycle stability. Summary of the Invention

[0004] In view of this, the primary purpose of this application is to provide a silicon-carbon composite material having a core and a coating layer, which not only has a high-strength core, but also can effectively alleviate the volume expansion of the material and improve the cycle stability of the material in lithium-ion batteries.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] One aspect of the present application provides a silicon-carbon composite material, comprising:

[0007] An inner core, the inner core comprising a composite carbon matrix and silicon material formed in pores and on a surface of the composite carbon matrix, the composite carbon matrix being composed of a first carbon phase and a second carbon phase, the first carbon phase being a phenolic resin-based carbon material and the second carbon phase being a fiber-based carbon material;

[0008] and a coating layer formed on the surface of the inner core, wherein the coating layer is a carbon layer.

[0009] Another aspect of the present application provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0010] S1, mixing the carbon sources of the first phase carbon and the second phase carbon, and sequentially performing pretreatment, carbonization, activation and pore formation to obtain a composite carbon matrix with a porous structure;

[0011] S2, introducing silicon source gas to deposit silicon material in the pores and surface of the composite carbon matrix by vapor deposition to obtain a core;

[0012] S3. Introduce silicon source gas and / or carbon source gas to form a coating layer on the surface of the inner core by vapor deposition.

[0013] Another aspect of the present application provides a lithium-ion battery, which contains the silicon-carbon composite material.

[0014] Beneficial effects of this application:

[0015] The silicon-carbon composite material in the present application has a core and a coating layer. The core is composed of a composite carbon matrix formed by a first-phase carbon-phenolic resin-based carbon material and a second-phase carbon-fiber-type carbon material, and silicon material is deposited in its pores and surface. Among them, the carbon sources of the first-phase carbon and the second-phase carbon are cross-linked with each other during the co-carbonization process, thereby forming a fiber-network carbon material, improving the structural strength of the porous carbon matrix, and effectively improving the phenomenon of silicon-carbon particles being broken by rolling during the process of making the electrode. In addition, the fiber axial molecular chain is highly oriented, and a graphite microcrystalline structure is formed after high-temperature carbonization. The material has good electrical conductivity and high stability. At the same time, the deposited silicon material is bound in the fiber network structure, so that silicon and carbon are firmly combined, which is conducive to the transmission of lithium ions and effectively alleviates the volume expansion of silicon. In the present application, a coating layer is formed on the surface of the core at the same time, thereby improving the conductivity of the silicon-carbon composite material, alleviating the volume expansion of the material, slowing down the capacity decay, and improving the cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is an SEM image of the silicon-carbon composite material in Example 1 of the present application.

[0017] Figure 2 This is the charge and discharge curve of the silicon-carbon composite material in Example 1 of the present application. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the embodiments of the present application. The technical solutions in the embodiments described below are exemplary and are only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the embodiments of the present application to obtain other embodiments without creative work, and these embodiments are also within the scope of protection of the present application.

[0019] The first aspect of the present application discloses a silicon-carbon composite material comprising a core and a coating formed on the surface of the core. The core comprises a composite carbon matrix and pores and a surface silicon material formed within the composite carbon matrix. The composite carbon matrix is ​​composed of a first carbon phase, a phenolic resin-based carbon material, and a second carbon phase, a fiber-based carbon material. The coating is a carbon layer.

[0020] In this application, a composite carbon matrix formed by a composite of a phenolic resin-based carbon material and a fiber-based carbon material is used as the core. Since the carbon sources of the two are cross-linked during the co-carbonization process, a fibrous network carbon material is formed, which can improve the structural strength of the porous carbon matrix and bind the silicon material in the fiber network structure, making the bond between silicon and carbon more solid, facilitating the transmission of lithium ions and effectively alleviating the volume expansion of silicon. Combined with the coating layer on the surface of the core, the silicon-carbon composite material can slow down the capacity decay and improve the stability of the cycle.

[0021] In some examples, in the composite carbon matrix, the mass percentage of the first phase carbon is 30-90 wt%, and the mass percentage of the second phase carbon is 10-70 wt%. For example, the mass percentage of the first phase carbon can be any value among 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, or a range between two values; for example, the mass percentage of the second phase carbon can be any value among 70 wt%, 65 wt%, 60 wt%, 55 wt%, 50 wt%, 45 wt%, 40 wt%, 35 wt%, 30 wt%, 25 wt%, 20 wt%, 15 wt%, 10 wt%, or a range between two values.

[0022] In this application, the phenolic resin-based carbon material refers to a porous carbon material obtained by carbonizing a phenolic resin as a carbon source. For example, the phenolic resin may be selected from at least one of o-cresol-formaldehyde resin, m-cresol-formaldehyde resin, phenol-formaldehyde resin, and glycerol-phenol-formaldehyde resin, but is not limited thereto.

[0023] In this application, the fibrous carbon material refers to a carbon material formed by pre-oxidation and high-temperature pyrolysis using an organic polymer precursor as a carbon source. It is generally obtained by carbonization using polyacrylonitrile, pitch, or the like as a carbon source, during which a carbon network structure is formed through reactions such as bond scission and cyclization. As an example, the raw material of the fibrous carbon material is at least one of polyacrylonitrile, pitch, and polystyrene, but is not limited thereto.

[0024] In this application, the pore volume of the composite carbon matrix formed is 0.1 to 3.0 cm 3 / g, for example, it can be 0.1cm 3 / g, 0.2cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.5cm 3 / g, 2.0cm 3 / g, 2.5cm 3 / g, 3.0cm 3 In some examples, preferably, the pore volume of the composite carbon matrix is ​​0.4 to 1.0 cm 3 / g.

[0025] In the present application, the average pore diameter of the formed composite carbon matrix is ​​0.1 to 20 nm, for example, any value selected from 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, and 20 nm, or a range thereof. In some examples, preferably, the average pore diameter of the composite carbon matrix is ​​1 to 10 nm.

[0026] In the present application, the average particle size Dv50 of the formed composite carbon matrix is ​​1-30 μm, for example, it can be any value among 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or a range value between any two of them.

[0027] By choosing appropriate pore volume, pore size and particle size, the primary effect, capacity and matrix strength of the material can be taken into account to achieve a balance of performance.

[0028] In this application, the silicon material is not particularly limited and can be any conventional type in the art. In some examples, the silicon material includes at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon. As an example, the silicon material can be amorphous silicon or polycrystalline silicon alone, or a combination of amorphous silicon and polycrystalline silicon.

[0029] In the present application, the coating layer is a carbon layer having a thickness of 0.1 to 100 nm, for example, any value selected from 0.1 nm, 0.5 nm, 1 nm, 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm, or a range therebetween. In some examples, preferably, the carbon layer has a thickness of 2 to 50 nm.

[0030] In some preferred embodiments, the coating layer further includes a silicon carbide layer, which is located between the core and the carbon layer, that is, the silicon carbide layer is coated on the surface of the core, and the carbon layer is coated on the surface of the silicon carbide layer. By introducing the silicon carbide layer, it is utilized to provide a stronger bonding force between the composite carbon matrix and the silicon material, thereby effectively improving the continuous generation of the SEI layer during the lithium ion insertion and extraction process and inhibiting the volume expansion of silicon. At the same time, the silicon carbide layer can provide protection for the core to prevent particle damage; the carbon layer has a higher elastic modulus, and its elasticity is used to absorb volume change stress. At the same time, the carbon layer acts as an electronic conductor to enhance the conductivity of the material. The carbon layer and the silicon carbide layer can synergistically improve the mechanical strength, anti-expansion ability and conductive properties of the material. As an example, the thickness of the silicon carbide layer is 0.05 to 50 nm, for example, any value selected from 0.05 nm, 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or a range therebetween. In some examples, preferably, the thickness of the silicon carbide layer is 0.5 to 15 nm.

[0031] In the present application, the particle size Dv50 of the silicon-carbon composite material is 0.2 to 50 μm, preferably 2 to 10 μm, for example, it can be any value among 2 μm, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm or a range between any two values; the specific surface area is 0.3 to 50 m 2 / g, preferably 0.5 to 10 m 2 / g, for example, it can be 1m 2 / g, 2m 2 / g、3m 2 / g、5m 2 / g、10m 2 Any value in g or any range between two values; total pore volume ≤ 0.2 cm 3 / g, preferably ≤0.01cm 3 / g, and the total pore volume is 0.001cm 3 / g, 0.002cm 3 / g, 0.003cm 3 / g, 0.005cm 3 / g, 0.01cm 3 Any value in / g or any range between them.

[0032] By appropriately selecting or adjusting the particle size, specific surface area, and pore volume of the silicon-carbon composite material, both processing performance and cycle performance can be taken into account, and those skilled in the art can make adjustments as needed.

[0033] In the present application, the silicon-carbon composite material has a silicon content of 1-80wt%, preferably 20-60wt%, for example, any value among 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or any range between the two; the carbon content is 10-90wt%, preferably 30-70wt%, for example, any value among 30wt%, 40wt%, 50wt%, 60wt%, or 70wt%, or any range between the two. The electrical properties of the silicon-carbon composite material can be optimized by appropriate silicon and carbon ratios.

[0034] The second aspect of the present application discloses a method for preparing the silicon-carbon composite material as described above, the main steps of which are as follows:

[0035] S1. After mixing the carbon sources of the first phase carbon and the second phase carbon, pretreatment, carbonization, activation and pore formation are sequentially performed to obtain a composite carbon matrix with a porous structure.

[0036] As an example, the carbon source of the first phase carbon is at least one of o-cresol-formaldehyde resin, m-cresol-formaldehyde resin, phenol-formaldehyde resin, and glycerol-phenol-formaldehyde resin; the carbon source of the second phase carbon is at least one of polyacrylonitrile, asphalt, and polystyrene. In the composite carbon matrix, the mass percentage of the first phase carbon is 30-90wt%, and the mass percentage of the second phase carbon is 10-70wt%.

[0037] After the two raw materials are mechanically mixed, they are pretreated. For example, the pretreatment is carried out in air at a temperature of 50 to 300°C, preferably 80 to 230°C, for a constant temperature of 0.5 to 30 hours. The pretreatment allows the first phase carbon source to undergo preliminary crosslinking and curing, while the second phase carbon source is pre-oxidized in air to form pre-oxidized fibers.

[0038] The pretreated mixture is then co-carbonized to undergo solid-state pyrolysis. Decomposition and cross-linking reactions occur simultaneously, with the first and second carbon phases cross-linking to form a fibrous network of carbon materials. The specific carbonization parameters can be adjusted or optimized based on actual conditions. For example, the carbonization temperature is 300-1200°C, preferably 500-1000°C, and the carbonization time is 0.5-20 hours, preferably 0.5-5 hours.

[0039] In this step, the activation pore formation is a conventional process for preparing porous carbon substrates in the art. As an example, the temperature is 300-1200°C, preferably 500-1000°C, and the time is 0.5-20 hours, preferably 1-6 hours. The activation pore formation method can be a physical activation method or a chemical activation method.

[0040] In some examples, the activation pore-forming method is a physical activation method, such as at least one of water vapor activation, carbon dioxide activation, and oxygen activation. The flow rate of the activation gas is preferably 0.5 to 20 L / min.

[0041] In other examples, the activation pore-forming method is a chemical activation method, and the activator used can be, for example, at least one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, phosphoric acid, hydrochloric acid, nitric acid, hydrofluoric acid, zinc chloride, sodium chloride, calcium chloride and magnesium chloride, but is not limited thereto. The specific ratio of the activator can be selected as needed or determined by experiment. As an example, the mass ratio of the activator to the carbonized material is 1: (0.1-10), preferably 1: (0.2-4), for example 1: 1, 1: 2, 1: 3.

[0042] S2. A silicon source gas is introduced to deposit silicon material in the pores and on the surface of the composite carbon matrix by vapor deposition to obtain a core.

[0043] In this step, silicon material is deposited in the pores and on the surface of the composite carbon matrix to obtain the core. The specific deposition method is vapor deposition well known in the art.

[0044] The silicon source gas used can be any conventional type in the art, including, but not limited to, at least one of monosilane, disilane, trisilane, butasilane, chlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. The flow rate of the silicon source gas can be selected as needed, for example, from 0.1 to 100 L / min, preferably from 1 to 20 L / min, such as 1 L / min, 2 L / min, 3 L / min, 5 L / min, 10 L / min, or 20 L / min, or any range therebetween.

[0045] In some examples, the deposition temperature of the silicon material is 350-700°C, preferably 450-600°C, for example, it can be any value among 450°C, 500°C, 550°C, 600°C, or a range between any two of them; the specific deposition method can be selected according to the amount of silicon material to be deposited. As an example, the deposition time is 0.5-20h, for example, it can be any value among 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, or a range between any two of them.

[0046] S3. Introduce silicon source gas and / or carbon source gas to form a coating layer on the surface of the inner core by vapor deposition.

[0047] In some examples, the coating layer in this step is a carbon layer, and only the carbon source gas needs to be introduced.

[0048] By way of example, the carbon source gas includes at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, methanol, ethanol, propanol, and benzene, but is not limited thereto. The flow rate of the carbon source gas can be selected as needed, for example, from 0.1 to 100 L / min, preferably from 1 to 10 L / min, for example, any value among 1 L / min, 2 L / min, 3 L / min, 5 L / min, and 10 L / min, or any range therebetween.

[0049] In some examples, the deposition temperature is 450-900°C, preferably 550-800°C, for example, it can be any value among 550°C, 600°C, 650°C, 700°C, 800°C or a range between any two of them; the specific deposition time can be adjusted as needed. As an example, the time is 0.2-10h, for example, 0.3h, 0.5h, 1h, 3h, 4h, etc.

[0050] In other examples, the coating layers in this step are sequentially formed into a silicon carbide layer and a carbon layer. First, a silicon source gas and a carbon source gas are introduced for co-deposition to form the silicon carbide layer; then, a carbon source gas is introduced to form the carbon layer. The types and flow rates of the silicon and carbon source gases used are as described above and are not detailed here.

[0051] In addition, it can be understood that the preparation steps of the present application are all carried out under a protective atmosphere. The protective atmosphere refers to the reaction under the condition of isolating oxygen. The protective atmosphere used is a gas that does not participate in the reaction and is inert or inactive with the reactants or products. Specific examples include nitrogen or at least one of rare gases. The rare gas refers to a Group 0 gas in the periodic table of chemical elements, for example, it can be at least one of argon, helium, neon, krypton, and xenon.

[0052] The third aspect of the present application discloses a lithium-ion battery comprising the aforementioned silicon-carbon composite material. Using the silicon-carbon composite material as a negative electrode material can significantly improve the capacity fade and cycle stability of the lithium-ion battery.

[0053] It is understandable that the lithium-ion battery here includes not only the negative electrode, but also the positive electrode, the separator and the electrolyte, etc., which can adopt conventional and arbitrary components in this field without special restrictions, so they will not be described one by one here.

[0054] The following are specific embodiments of the present application. It should be noted that the following specific embodiments are only for illustrative purposes and do not limit the scope of the present application in any way.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0056] In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0057] Example 1

[0058] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, and the specific steps are as follows:

[0059] S1. Phenolic resin and polyacrylonitrile were mixed in a mass ratio of 1:1 (a total of 2 kg), placed in a drying oven, and pretreated in air at 180°C for 5 hours; the pretreated mixture was placed in a high-temperature furnace, heated to 700°C under nitrogen protection and carbonized for 3 hours; the carbonized material was then mixed evenly with a KOH activator in a ratio of 1:2, placed in a rotary kiln, heated to 900°C for activation for 2 hours, activated and pore-forming, and discharged after cooling. The material was crushed to obtain a composite carbon matrix with a porous structure;

[0060] S2. Placing the composite carbon matrix in a fluidized bed apparatus, raising the temperature to 500° C. under nitrogen protection, introducing monosilane as a silicon source gas, with a deposition time of 4 h and a flow rate of 3 L / min, depositing the silicon material in the pores and surface of the composite carbon matrix to obtain a core;

[0061] S3, further heating the core material prepared in step S2 to 680° C., and then simultaneously introducing monosilane gas and acetylene gas into the fluidized bed apparatus for co-deposition, with a monosilane flow rate of 2 L / min, an acetylene flow rate of 2 L / min, and a ventilation time of 0.5 h to form a silicon carbide coating layer, thereby obtaining a silicon carbide-coated core material;

[0062] S4. Place the material prepared in step S3 in a rotary kiln, heat it to 550° C., introduce acetylene gas as a carbon source at a flow rate of 3 L / min and a ventilation time of 2 h to form a carbon coating layer to obtain a silicon-carbon composite material.

[0063] Example 2

[0064] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same method as in Example 1, except that in step S1, the mass ratio of phenolic resin to polyacrylonitrile is 1:0.5. Other process steps and parameter conditions are the same as in Example 1.

[0065] Example 3

[0066] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, except that in step S1, the mass ratio of phenolic resin to asphalt is 1:0.2. Other process steps and parameter conditions are the same as in Example 1.

[0067] Example 4

[0068] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, except that in step S1, the mass ratio of o-cresol-formaldehyde resin to polyacrylonitrile is 1:2. Other process steps and parameter conditions are the same as in Example 1.

[0069] Example 5

[0070] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, except that in step S1, the mass ratio of phenolic resin to polystyrene is 1:5. Other process steps and parameter conditions are the same as in Example 1.

[0071] Example 6

[0072] The embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, with the only difference being that in step S2, the monosilane ventilation deposition time is 5 hours. The other process steps and parameter conditions are the same as in Example 1.

[0073] Example 7

[0074] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, except that in step S3, the co-deposition time of monosilane and acetylene gas is 1 hour. The other process steps and parameter conditions are the same as in Example 1.

[0075] Example 8

[0076] This embodiment discloses a silicon-carbon composite material and a preparation method thereof, using the same implementation as in Example 1, except that no silicon carbide coating layer is formed in step S3. Other process steps and parameter conditions are the same as in Example 1.

[0077] Example 9

[0078] This embodiment discloses a silicon-carbon composite material and a method for preparing the same. The method employs the same process as in Example 1, with the only differences being that in step S3, the co-deposition time of monosilane and acetylene gas is 0.2 hours, and in step S4, the deposition time of the carbon source gas is 0.3 hours. All other process steps and parameters are the same as in Example 1.

[0079] Example 10

[0080] This embodiment discloses a silicon-carbon composite material and a method for preparing the same. The method employs the same process as in Example 1, with the only differences being that in step S3, the co-deposition time of monosilane and acetylene gas is 0.2 hours, and in step S4, the deposition time of the carbon source gas is 2 hours. All other process steps and parameters are the same as in Example 1.

[0081] Example 11

[0082] This embodiment discloses a silicon-carbon composite material and a method for preparing the same. The method employs the same process as in Example 1, with the only differences being that in step S3, the co-deposition time of monosilane and acetylene gas is 2 hours, and in step S4, the deposition time of the carbon source gas is 3.5 hours. All other process steps and parameters are the same as in Example 1.

[0083] Example 12

[0084] This embodiment discloses a silicon-carbon composite material and a method for preparing the same. The method employs the same process as in Example 1, with the only differences being that in step S3, the co-deposition time of monosilane and acetylene gas is 0.5 hours, and in step S4, the deposition time of the carbon source gas is 5 hours. All other process steps and parameters are the same as in Example 1.

[0085] Comparative Example 1

[0086] This comparative example adopts the same method as Example 1, except that polyacrylonitrile is replaced with an equal mass of phenolic resin, i.e., all phenolic resin is used, and step S3 is not performed. Other process steps and parameter conditions are the same as Example 1.

[0087] Comparative Example 2

[0088] This comparative example adopts the same implementation as Example 1, with the only difference being that polyacrylonitrile is replaced with an equal mass of phenolic resin, i.e., all phenolic resin is used. The other process steps and parameter conditions are the same as those in Example 1.

[0089] Performance Testing

[0090] (1) Specific surface area, pore volume and pore diameter test: The pore volume and pore diameter were measured using the American Quantachrome Autosorb-iQ fully automatic specific surface area and pore diameter analyzer. The DFT model was used to fit the data. The test results are shown in Table 1.

[0091] (2) Crush force test: A single particle mechanical property test was conducted. The indenter was loaded onto a single particle to apply pressure to crush it. The average value of 10 particles was measured. The test results are shown in Table 1.

[0092] (3) Coating thickness: The coating thickness can be measured by SEM or TEM using FIB-SEM slices. The test results are shown in Table 1.

[0093] (4) Test of element content: Si content was measured by ICP elemental analysis; C content was measured by carbon-sulfur analyzer. The test results are shown in Table 2.

[0094] (5) Electrochemical test: Silicon-carbon negative electrode material, conductive carbon black and binder LA133 were mixed into a slurry in a mass ratio of 8:1:1 and evenly coated on copper foil. After drying, it was prepared into a negative electrode plate, with metallic lithium as the counter electrode; the composition of the electrolyte: 1 mol / L LiPF6, the solvent is ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and the volume ratio of EC to EMC is 1:2; modified polyethylene (PE) was used as a separator to assemble a button cell, and its electrochemical performance was tested on a blue battery test cabinet. The charge and discharge system was as follows: standing for 10 hours, testing at a current density of 0.1C, the discharge cut-off voltage was 0.005V, and the charge cut-off voltage was 1.5V. The test results are shown in Table 2.

[0095] Table 1 Test results of material specific surface area, pore volume, particle size, coating layer and crushing force

[0096]

[0097]

[0098] It can be seen from the test results in Table 1 that compared with Comparative Example 2, the silicon-carbon composite materials of Examples 1-12 have lower specific surface area, indicating that the silicon carbide coating can reduce the specific surface area of ​​the material, thereby improving the interface problems of the material during the charge and discharge cycle; compared with Comparative Examples 1 and 2, the silicon-carbon composite materials of Examples 1-12 have higher crushing force, indicating that the composite carbon matrix formed by the first phase carbon and the second phase carbon is beneficial to improving the structural strength of the silicon-carbon material and improving the material's anti-expansion ability.

[0099] also, Figure 1The SEM image of the silicon-carbon composite material prepared in Example 1 of the present application is shown. As can be seen from the image, the material is granular, has a smooth surface, has no obvious macroporous structure, and has a uniform particle size distribution.

[0100] Table 2 Material element content and electrical properties test

[0101]

[0102]

[0103] The test results in Table 2 show that the silicon-carbon anode materials prepared using Examples 1-12 exhibit less expansion upon full charge compared to Comparative Examples 1 and 2, indicating that using a composite carbon source to prepare the carbon matrix is ​​beneficial for reducing silicon volume expansion and improving cycle performance. Furthermore, as a preferred approach, the introduction of a silicon carbide coating can improve the continuous formation of the SEI film at the material interface during cycling, further enhancing the material's capacity retention and cycle performance.

[0104] Further, Figure 2 The charge-discharge curve of the silicon-carbon composite material prepared in Example 1 of the present application is shown. It can be seen that the capacity of the material is 1891.3 mAh / g and the first efficiency is 92.2%, indicating that the silicon-carbon composite material prepared in the present application has excellent electrochemical properties.

[0105] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A silicon-carbon composite material, characterized in that: include: An inner core, the inner core comprising a composite carbon matrix and a silicon material formed in the pores and surface of the composite carbon matrix, the composite carbon matrix being composed of a first phase carbon and a second phase carbon, the first phase carbon being a phenolic resin-based carbon material, and the second phase carbon being a fiber-based carbon material; and a coating layer formed on the surface of the inner core, wherein the coating layer is a carbon layer.

2. The silicon-carbon composite material according to claim 1, wherein In the composite carbon matrix, the mass percentage of the first phase carbon is 30-90 wt %, and the mass percentage of the second phase carbon is 10-70 wt %.

3. The silicon-carbon composite material according to claim 1, wherein The carbon source of the first phase carbon is at least one of o-cresol-formaldehyde resin, m-cresol-formaldehyde resin, phenol-formaldehyde resin, and glycerol phenol-formaldehyde resin; And / or, the carbon source of the second phase carbon is at least one of polyacrylonitrile, asphalt, and polystyrene.

4. The silicon-carbon composite material according to claim 1, wherein The pore volume of the composite carbon matrix is ​​0.1-3.0 cm 3 / g, the average pore diameter is 0.1-20nm, and the average particle size Dv50 is 1-30μm.

5. The silicon-carbon composite material according to claim 1, wherein The silicon material includes at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon.

6. The silicon-carbon composite material according to claim 1, wherein The thickness of the coating layer is 0.1-100 nm.

7. The silicon-carbon composite material according to claim 1, wherein The coating layer further includes a silicon carbide layer, and the silicon carbide layer is located between the core and the carbon layer; Preferably, the thickness of the silicon carbide layer is 0.05-50 nm.

8. The silicon-carbon composite material according to any one of claims 1 to 7, wherein: The particle size Dv50 of the silicon-carbon composite material is 0.2 to 50 μm, and the specific surface area is 0.3 to 50 m 2 / g, total pore volume ≤ 0.2cm 3 / g; And / or, in the silicon-carbon composite material, the silicon content is 1-80 wt %, and the carbon content is 10-90 wt %.

9. A method for preparing the silicon-carbon composite material according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, mixing the carbon sources of the first phase carbon and the second phase carbon, and sequentially performing pretreatment, carbonization, and activation to form pores to obtain a composite carbon matrix with a porous structure; S2, introducing silicon source gas to deposit silicon material in the pores and surface of the composite carbon matrix by vapor deposition to obtain a core; S3, introducing silicon source gas and / or carbon source gas to form a coating layer on the surface of the core by vapor deposition; Preferably, in step S1, the carbonization temperature is 300-1200° C. and the time is 0.5-20 h; and / or the activation pore-forming temperature is 300-1200° C. and the time is 0.5-20 h; Preferably, in step S1, the activation pore-forming method includes a physical activation method or a chemical activation method; Preferably, the activation gas introduced in the physical activation method is at least one of water vapor, carbon dioxide, and oxygen; Preferably, the chemical activator used in the chemical activation method is at least one of potassium oxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, phosphoric acid, hydrochloric acid, nitric acid, hydrofluoric acid, zinc chloride, sodium chloride, calcium chloride, and magnesium chloride; Preferably, in step S2, the deposition temperature of the silicon material is 350-700° C., and the deposition time is 0.5-20 h; Preferably, the silicon source gas is at least one of monosilane, disilane, trisilane, butasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane; and / or the flow rate of the silicon source gas is 0.1 to 100 L / min; Preferably, the carbon source gas is at least one of acetylene, methane, ethane, propane, butane, ethylene, propylene, butene, methanol, ethanol, propanol and benzene; and / or the flow rate of the carbon source gas is 0.1 to 100 L / min; Preferably, the deposition temperature of the coating layer is 450-900°C, and the deposition time is 0.2-10h; Preferably, steps S1 to S3 are all performed in a protective atmosphere, and the protective atmosphere is at least one of nitrogen and a rare gas.

10. A lithium ion battery, characterized in that: Contains the silicon-carbon composite material according to any one of claims 1 to 8.

Images