A silicon-carbon negative electrode material and its preparation method and application

Abstract

The present invention belongs to the technical field of secondary batteries, and specifically relates to a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof. The present invention provides a preparation method for a silicon-carbon negative electrode material, comprising the following steps: using a chemical vapor deposition method to perform a first carbon coating on a metal compound to obtain a porous carbon matrix precursor; the metal compound comprises one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate, and calcium carbonate; acid-washing the porous carbon matrix precursor to obtain a porous carbon matrix; using a chemical vapor deposition method to perform silicon deposition on the porous carbon matrix to obtain a silicon-carbon precursor; and using an organic carbon source cracking method to perform a second carbon coating on the silicon-carbon precursor to obtain the silicon-carbon negative electrode material. The silicon-carbon negative electrode material obtained by the preparation method provided by the present invention exhibits excellent specific capacity and cycle stability when used in lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Currently, lithium-ion battery technology is limited by its energy density, resulting in limited range for electric vehicles. This creates range anxiety for users and severely restricts their market share. Improving battery energy density primarily involves optimizing battery structure and increasing the energy density of materials. Anode materials account for approximately 16% of a battery's mass, and using high-capacity anode materials is one effective way to increase battery energy density.

[0003] Traditional lithium-ion battery negative electrode materials are graphite materials, but their theoretical capacity is low (372mAh / g), which cannot meet market demand. Silicon-based negative electrode materials have a similar delithiation potential to graphite and a higher theoretical specific capacity (4200mAh / g). As lithium battery negative electrodes, they have great application potential in improving the performance of power batteries. However, silicon-based materials have a huge volume effect (>300%) during the charge and discharge process, which leads to the instability of the solid electrolyte interface film formed, and the particles are prone to rupture and pulverization, thereby losing electrical contact with the current collector, ultimately leading to rapid attenuation of electrode capacity and low coulombic efficiency, resulting in a sharp decline in cycle performance. Therefore, how to improve cycle performance is of great significance to the application of silicon materials in lithium-ion batteries. Summary of the Invention

[0004] The object of the present invention is to provide a silicon-carbon negative electrode material and a preparation method thereof. The silicon-carbon negative electrode material obtained by the preparation method provided by the present invention has excellent specific capacity and cycle stability.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0007] A metal compound is first carbon-coated by chemical vapor deposition to obtain a porous carbon matrix precursor; the metal compound comprises one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate and calcium carbonate;

[0008] acid-washing the porous carbon matrix precursor to obtain a porous carbon matrix;

[0009] Depositing silicon on the porous carbon matrix using chemical vapor deposition to obtain a silicon-carbon precursor;

[0010] The silicon-carbon precursor is subjected to a second carbon coating by cracking an organic carbon source to obtain the silicon-carbon negative electrode material.

[0011] Preferably, the median particle size of the metal compound is 10 nm to 100 μm;

[0012] The carbon source used for the first carbon coating includes one or more of methane, ethane, propane, ethylene and acetylene; the gas flow rate of the carbon source is 0.1 to 5 L / min;

[0013] The temperature of the first carbon coating is 700-900° C., and the time is 0.5-12 hours; the first carbon coating is performed in an inert gas.

[0014] Preferably, the acid used for pickling is one or more of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid;

[0015] The concentration of the acid is 0.5 to 5 mol / L; the molar ratio of the acid to the metal compound is greater than 1.2:1;

[0016] The pickling time is 1 to 12 hours, and the temperature is 25 to 100°C.

[0017] Preferably, the porosity of the porous carbon matrix is ​​greater than 50%, and the average pore size is 10-100 nm.

[0018] Preferably, the silicon source used for the silicon deposition includes one or more of monosilane, dimethylsilane, chlorosilane, chloromethylsilane and dichlorosilane; the gas flow rate of the silicon source is 0.3 to 2 L / min;

[0019] The silicon deposition temperature is 400-700° C., and the time is 0.5-24 hours; the silicon deposition is carried out in an inert gas.

[0020] Preferably, the organic carbon source used for the second carbon coating includes one or more of methane, acetylene, toluene, glucose, petroleum asphalt, mesophase asphalt, phenolic resin and polyacrylonitrile;

[0021] The temperature of the second carbon coating is 300-900° C., and the time is 0.5-12 hours; the second carbon coating is performed in an inert gas.

[0022] The present invention also provides a silicon-carbon negative electrode material obtained by the preparation method described in the above technical solution, wherein the silicon-carbon negative electrode material has a core-shell structure;

[0023] The core of the core-shell structure includes a porous carbon matrix and nano-silicon particles; the nano-silicon particles are distributed in the pores and surface of the porous carbon matrix;

[0024] The shell of the core-shell structure is a carbon coating layer.

[0025] Preferably, the specific surface area of ​​the silicon-carbon negative electrode material is 1 to 10 m 2 / g, median particle size is 3-20 μm;

[0026] The mass percentage of silicon element in the silicon-carbon negative electrode material is 25-75%, and the mass percentage of carbon element is 25-75%.

[0027] Preferably, the nano-silicon particles include amorphous silicon and / or crystalline silicon; the median particle size of the nano-silicon particles is less than 50 nm;

[0028] The mass percentage of the carbon coating layer in the silicon-carbon negative electrode material is 1-10%.

[0029] The present invention also provides the use of the silicon-carbon negative electrode material described in the above technical solution in a lithium-ion battery.

[0030] The present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps: using a chemical vapor deposition method to perform a first carbon coating on a metal compound to obtain a porous carbon matrix precursor; the metal compound includes one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate and calcium carbonate; acid washing the porous carbon matrix precursor to obtain a porous carbon matrix; using a chemical vapor deposition method to deposit silicon on the porous carbon matrix to obtain a silicon-carbon precursor; and using an organic carbon source cracking method to perform a second carbon coating on the silicon-carbon precursor to obtain the silicon-carbon negative electrode material. The present invention uses metal compound particles as a template, uses chemical vapor deposition carbon and acid washing technology to prepare a porous carbon material as a matrix, and utilizes its advantages such as excellent mechanical properties, good conductivity, stable chemical properties and large pore volume. As a silicon-based material carrier, it can effectively buffer volume expansion, and by chemical vapor deposition of silicon on the porous carbon, the particle size of the silicon particles can be reduced. Finally, a second carbon coating is performed to prepare a silicon-carbon negative electrode material. The porous carbon matrix obtained by the preparation method provided by the present invention has a higher porosity, and the silicon-carbon negative electrode material has a smaller specific surface area and excellent conductivity. It exhibits superior specific capacity and cycle stability when used in lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is a SEM image of the porous carbon matrix obtained in Example 1;

[0033] Figure 2 1 is a pore size distribution diagram of the porous carbon matrix obtained in Example 1;

[0034] Figure 3 This is an SEM image of the silicon-carbon negative electrode material obtained in Example 1;

[0035] Figure 4 This is the XRD diffraction pattern of the silicon-carbon negative electrode material obtained in Example 1;

[0036] Figure 5 This is a charge and discharge curve diagram of the silicon-carbon negative electrode material obtained in Example 1. DETAILED DESCRIPTION

[0037] The present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0038] A metal compound is first carbon-coated by chemical vapor deposition to obtain a porous carbon matrix precursor; the metal compound comprises one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate and calcium carbonate;

[0039] acid-washing the porous carbon matrix precursor to obtain a porous carbon matrix;

[0040] Depositing silicon on the porous carbon matrix using chemical vapor deposition to obtain a silicon-carbon precursor;

[0041] The silicon-carbon precursor is subjected to a second carbon coating by cracking an organic carbon source to obtain the silicon-carbon negative electrode material.

[0042] In the present invention, unless otherwise specified, the raw material components are commercially available products well known to those skilled in the art.

[0043] The present invention adopts a chemical vapor deposition method to perform a first carbon coating on a metal compound to obtain a porous carbon matrix precursor.

[0044] In the present invention, the metal compound includes one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate and calcium carbonate, preferably includes one or more of potassium oxide, calcium oxide, magnesium oxide, zinc oxide, sodium carbonate and calcium carbonate, more preferably includes one or more of calcium oxide, zinc oxide, sodium carbonate and calcium carbonate; when the metal compound is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and can be mixed in any ratio. The median particle size of the metal compound is preferably 10nm to 100μm, more preferably 100nm to 50μm, and most preferably 1 to 10μm.

[0045] In the present invention, the carbon source used for the first carbon coating preferably includes one or more of methane, ethane, propane, ethylene, and acetylene, more preferably includes one or more of methane, ethane, ethylene, and acetylene, and most preferably includes one or more of methane, ethane, and acetylene. When the carbon source is two or more of the above-mentioned specific selections, the present invention does not have any special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The gas flow rate of the carbon source is preferably 0.1 to 5 L / min, more preferably 0.5 to 4 L / min, and most preferably 0.8 to 3 L / min.

[0046] In the present invention, the heating rate of the first carbon coating is preferably 1-10°C / min, more preferably 2-8°C / min, and most preferably 4-7°C / min; the temperature is preferably 700-900°C, more preferably 750-870°C, and most preferably 800-850°C; the time is preferably 0.5-12h, more preferably 1-10h, and most preferably 3-8h; the first carbon coating is preferably carried out in an inert gas; the inert gas preferably includes nitrogen, helium, neon or argon, more preferably includes nitrogen, helium or argon, and most preferably includes nitrogen or argon; the flow rate of the inert gas is preferably 0.3-2L / min, more preferably 0.5-1.8L / min, and most preferably 1-1.5L / min.

[0047] In the present invention, the first carbon coating is preferably carried out using a chemical vapor deposition furnace; the rotation speed of the chemical vapor deposition furnace is preferably 0.2 to 2 r / min, more preferably 0.5 to 1.5 r / min, and most preferably 0.8 to 1.3 r / min; the pressure in the furnace is preferably 0 to 0.3 MPa, more preferably 0.1 to 0.3 MPa, and most preferably 0.1 to 0.2 MPa.

[0048] The mass ratio of the metal compound to carbon in the porous carbon matrix precursor is preferably 1:1-5, more preferably 1:2-4, and most preferably 1:2-3.

[0049] After the first carbon coating is completed, the present invention performs acid washing on the porous carbon matrix precursor to obtain a porous carbon matrix.

[0050] In the present invention, the acid used for pickling is preferably one or more of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid, more preferably dilute hydrochloric acid and / or dilute nitric acid, and most preferably dilute hydrochloric acid. When the acid is two or more of the above-mentioned specific options, the present invention does not have any special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The concentration of the acid is preferably 0.5 to 5 mol / L, more preferably 1 to 4 mol / L, and most preferably 2 to 3 mol / L. The molar ratio of the acid to the metal compound is preferably greater than 1.2:1, more preferably 1.2 to 5:1, and most preferably 2 to 4:1.

[0051] In the present invention, the pickling time is preferably 1 to 12 hours, more preferably 2 to 10 hours, most preferably 4 to 8 hours; the temperature is preferably 25 to 100°C, more preferably 40 to 90°C, most preferably 50 to 80°C.

[0052] In the present invention, the equipment used for pickling is preferably a magnetic stirrer and / or a mechanical stirrer, more preferably a magnetic stirrer; the speed of the equipment used for pickling is preferably 100-1000r / min, more preferably 200-800r / min, most preferably 400-600r / min.

[0053] After the pickling is completed, the present invention further comprises water washing, drying and screening in sequence.

[0054] In the present invention, the solvent used for the water washing is preferably pure water; the equipment used for the water washing is preferably a magnetic stirrer and / or a mechanical stirrer, more preferably a magnetic stirrer; the speed of the equipment used for the water washing is preferably 100-1000 r / min, more preferably 200-800 r / min, most preferably 400-600 r / min; the time for the water washing is preferably 0.5-5 h, more preferably 1-4 h, most preferably 2-3 h; the temperature is preferably 25-100° C., more preferably 40-90° C., most preferably 50-80° C.

[0055] In the present invention, the equipment used for the drying is preferably a blast drying oven; the drying temperature is preferably 100-200°C, more preferably 120-180°C, and most preferably 140-160°C.

[0056] In the present invention, the equipment used for screening is preferably an ultrasonic vibration screen; the mesh size of the screening equipment is preferably 20 to 2000 meshes, more preferably 100 to 1500 meshes, and most preferably 200 to 1000 meshes.

[0057] In the present invention, the porosity of the porous carbon matrix is ​​preferably greater than 50%, more preferably 50-90%, and most preferably 60-80%; the average pore size is preferably 10-100 nm, more preferably 20-80 nm, and most preferably 40-60 nm; the central particle size of the porous carbon matrix is ​​preferably 6-100 μm, more preferably 10-80 μm, and most preferably 40-60 μm.

[0058] In this invention, a special pore-forming technique (acid washing) results in a porous carbon matrix material with a pore size distribution dominated by mesopores, with an average pore size of 10 to 100 nm. This increased pore size and porosity facilitates the deposition of nano-silicon particles and effectively mitigates the volume expansion effect during the charge and discharge process of lithium-ion batteries, resulting in the material having better dynamic performance.

[0059] After obtaining the porous carbon matrix, the present invention uses chemical vapor deposition to deposit silicon on the porous carbon matrix to obtain a silicon-carbon precursor.

[0060] In the present invention, the silicon source used for silicon deposition preferably includes one or more of monosilane, dimethylsilane, chlorosilane, chloromethylsilane, and dichlorosilane, more preferably includes one or more of monosilane, dimethylsilane, chlorosilane, and dichlorosilane, and most preferably includes one or more of monosilane, dimethylsilane, and dichlorosilane. When the silicon source is two or more of the above-mentioned specific selections, the present invention does not have any particular limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The gas flow rate of the silicon source is preferably 0.3 to 2 L / min, more preferably 0.5 to 1.8 L / min, and most preferably 1 to 1.5 L / min.

[0061] In the present invention, the heating rate of the silicon deposition is preferably 1-10°C / min, more preferably 2-8°C / min, and most preferably 4-7°C / min; the temperature is preferably 400-700°C, more preferably 450-650°C, and most preferably 500-600°C; the time is preferably 0.5-24h, more preferably 3-20h, and most preferably 5-15h; the silicon deposition is preferably carried out in an inert gas; the inert gas preferably includes nitrogen, helium, neon or argon, more preferably includes nitrogen, helium or argon, and most preferably includes nitrogen or argon; the gas flow rate of the inert gas is preferably 0.3-2L / min, more preferably 0.5-1.8L / min, and most preferably 1-1.5L / min.

[0062] In the present invention, the silicon deposition is preferably carried out using a chemical vapor deposition furnace; the rotation speed of the chemical vapor deposition furnace is preferably 0.2 to 2 r / min, more preferably 0.5 to 1.5 r / min, and most preferably 0.8 to 1.3 r / min; the pressure in the furnace is preferably 0 to 0.3 MPa, more preferably 0.1 to 0.3 MPa, and most preferably 0.1 to 0.2 MPa.

[0063] After the silicon is deposited, the present invention further preferably includes oxidation. In the present invention, the oxidation temperature is preferably 25 to 100°C, more preferably 40 to 90°C, and most preferably 50 to 80°C; the oxidation time is preferably 0.5 to 10 hours, more preferably 2 to 8 hours, and most preferably 4 to 6 hours; the oxidation is preferably carried out in air; the air is preferably dry compressed air; the humidity of the air is 0 to 20%, more preferably 3 to 18%, and most preferably 5 to 15%; the flow rate is preferably 0.1 to 20 L / min, more preferably 1 to 15 L / min, and most preferably 5 to 10 L / min.

[0064] In the present invention, the role of the oxidation is to form a small amount of silicon oxide on the surface of the nano-silicon, thereby preventing the highly active nano-silicon from being violently oxidized and spontaneously combusted when exposed to the air.

[0065] In the present invention, silicon deposition adopts chemical vapor deposition technology, so that the median particle size of the prepared nano-silicon particles is not greater than 50nm, and good cycle performance can be achieved during the charge and discharge process. On the other hand, by changing the process parameters of the vapor deposition furnace, the particle size, crystal structure and quality of the deposited nano-silicon particles can be adjusted.

[0066] After obtaining the silicon-carbon precursor, the present invention uses a method of cracking an organic carbon source to perform a second carbon coating on the silicon-carbon precursor to obtain the silicon-carbon negative electrode material.

[0067] In the present invention, the organic carbon source used in the second carbon coating preferably includes one or more of methane, acetylene, toluene, glucose, petroleum asphalt, mesophase asphalt, phenolic resin and polyacrylonitrile, more preferably includes one or more of methane, acetylene, toluene, glucose, petroleum asphalt, phenolic resin and polyacrylonitrile, most preferably includes one or more of methane, acetylene, toluene, petroleum asphalt and polyacrylonitrile; when the organic carbon source is two or more of the above-mentioned specific selections, the present invention does not have any special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The second carbon coating preferably includes gas phase coating, liquid phase coating or solid phase coating, more preferably includes gas phase coating or liquid phase coating, and most preferably includes gas phase coating.

[0068] In the present invention, the heating rate of the second carbon coating is preferably 1 to 10°C / min, more preferably 2 to 8°C / min, and most preferably 4 to 7°C / min; the temperature is preferably 300 to 900°C, more preferably 400 to 800°C, and most preferably 500 to 700°C; the time is preferably 0.5 to 12 hours, more preferably 3 to 10 hours, and most preferably 5 to 8 hours; the second carbon coating is preferably carried out in an inert gas. The inert gas preferably includes nitrogen, helium, neon or argon, more preferably includes nitrogen, helium or argon, and most preferably includes nitrogen or argon; the flow rate of the inert gas is preferably 0.1 to 20 L / min, more preferably 1 to 15 L / min, and most preferably 5 to 10 L / min.

[0069] In the present invention, the second carbon coating is preferably a gas-phase organic carbon source coating, and the gas-phase organic carbon source coating is preferably carried out in a chemical vapor deposition furnace; the flow rate of the gas-phase organic carbon source is preferably 0.1-20 L / min, more preferably 1-15 L / min, and most preferably 5-10 L / min; the rotation speed of the chemical vapor deposition furnace is preferably 0.2-2 r / min, more preferably 0.5-1.5 r / min, and most preferably 0.8-1.3 r / min; the pressure in the furnace is preferably 0-0.3 MPa, more preferably 0.1-0.3 MPa, and most preferably 0.1-0.2 MPa.

[0070] In the present invention, the second carbon coating process is preferably: fully contacting the silicon-carbon precursor with an organic carbon source, and pyrolyzing the organic carbon source at high temperature to obtain the silicon-carbon negative electrode material.

[0071] In the present invention, the second carbon coating can isolate the nano-silicon particles from contact with water, avoid gas production in the water slurry during battery preparation, have a good slurry process, and avoid direct contact with the electrolyte to produce excessive SEI film during the charge and discharge process, so that the battery maintains good cycle performance and other electrochemical properties during charge and discharge. On the other hand, by limiting the process parameters of the second carbon coating, the thickness of the coating layer and the specific surface area of ​​the silicon-carbon negative electrode material can be adjusted, thereby improving the conductivity and kinetic properties of the silicon-carbon negative electrode material.

[0072] The preparation method of the silicon-carbon negative electrode material provided by the present invention uses metal compound particles as a template, and uses chemical vapor deposition carbon and pickling technology to prepare a porous carbon material as a matrix. The advantages of the porous carbon material, such as excellent mechanical properties, good electrical conductivity, stable chemical properties and large pore volume, are utilized. As a silicon-based material carrier, it can effectively buffer volume expansion, and by chemical vapor deposition of silicon on the porous carbon, the particle size of the silicon particles can be reduced. Finally, a second carbon coating is performed to prepare the silicon-carbon negative electrode material. The porous carbon matrix obtained by the preparation method provided by the present invention has a higher porosity, and the silicon-carbon negative electrode material has a smaller specific surface area and excellent electrical conductivity. It is used in lithium-ion batteries to exhibit superior specific capacity and cycle stability.

[0073] The present invention also provides a silicon-carbon negative electrode material obtained by the preparation method described in the above technical solution, wherein the silicon-carbon negative electrode material has a core-shell structure;

[0074] The core of the core-shell structure includes a porous carbon matrix and nano-silicon particles; the nano-silicon particles are distributed in the pores and surface of the porous carbon matrix;

[0075] The shell of the core-shell structure is a carbon coating layer.

[0076] In the present invention, the specific surface area of ​​the silicon-carbon negative electrode material is preferably 1 to 10 m 2 / g, more preferably 2 to 8 m 2 / g, and the most preferred range is 4 to 6 m 2 / g; the median particle size is preferably 3-20 μm, more preferably 5-18 μm, and most preferably 10-15 μm; the mass percentage of silicon element in the silicon-carbon negative electrode material is preferably 25-75%, more preferably 35-65%, and most preferably 45-55%; the mass percentage of carbon element is preferably 25-75%, more preferably 35-65%, and most preferably 45-55%.

[0077] In the present invention, the nano-silicon particles preferably include amorphous silicon and / or crystalline silicon, more preferably amorphous silicon. When the nano-silicon particles are two or more of the above-mentioned specific materials, the present invention does not impose any particular restrictions on the ratio of the above-mentioned materials; they can be mixed in any ratio. The median particle size of the nano-silicon particles is preferably 50 nm or less, more preferably 0.1 to 40 nm, and most preferably 10 to 30 nm.

[0078] In the present invention, the number of layers of the carbon coating layer is preferably at least one, more preferably 1 to 5 layers, and most preferably 2 to 3 layers; the thickness of a single layer is preferably greater than 100 nm, more preferably 100 nm to 10 μm, and most preferably 500 nm to 5 μm; the mass percentage of the carbon coating layer in the silicon-carbon negative electrode material is preferably 1 to 10%, more preferably 2 to 8%, and most preferably 4 to 6%; the carbon coating layer is also preferably filled in the pores of the porous carbon matrix.

[0079] The silicon-carbon negative electrode material provided by the present invention, when used as the negative electrode active material of a secondary battery, can significantly improve the energy density of the battery and has excellent electrochemical and kinetic properties.

[0080] The present invention also provides the use of the silicon-carbon negative electrode material described in the above technical solution in a lithium-ion battery.

[0081] The present invention does not have any special limitation on the application process, and the application can be carried out in a manner well known to those skilled in the art.

[0082] In order to further illustrate the present invention, the silicon-carbon negative electrode material provided by the present invention, its preparation method and application are described in detail below with reference to the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present invention.

[0083] Example 1

[0084] (1) Preparation of porous carbon matrix: 1 kg of magnesium oxide powder was placed in a CVD (chemical vapor deposition) furnace with a median particle size of 4 μm. Nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 800°C at a rate of 5°C / min. Acetylene was introduced at 0.8 L / min and kept warm for 12 h to uniformly coat the deposited carbon in the magnesium oxide powder. The temperature was then lowered to room temperature. 100 L of 1 mol / L dilute hydrochloric acid was added to the carbon-coated magnesium oxide. The mixture was acid-washed at 80°C for 10 h at 400 r / min in a magnetic stirrer to form pores. The mixture was then washed with water at 80°C for 2 h at 400 r / min until neutral. The mixture was dried at 140°C and sieved through 325 mesh to obtain a porous carbon matrix.

[0085] (2) Silicon deposition: The porous carbon substrate was placed in a CVD furnace and nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 500 °C at a rate of 5 °C / min, and silane was introduced at a flow rate of 0.8 L / min. The temperature was kept at this temperature for 20 h to deposit nanosilicon on the surface and pores of the porous carbon substrate. The temperature was then lowered to room temperature to obtain a silicon-carbon precursor.

[0086] (3) Preparation of silicon-carbon negative electrode material: The silicon-carbon precursor in step (2) is placed in a CVD furnace, and nitrogen is introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed is 1.0 r / min until the oxygen content in the CVD furnace is less than 100 ppm. The temperature is raised to 700°C at a rate of 5°C / min, and acetylene is introduced at 0.8 L / min. The temperature is kept at 700°C for 6 h to uniformly coat the deposited carbon on the surface and pores of the silicon-carbon precursor. The temperature is then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0087] Example 2

[0088] (1) Preparation of porous carbon matrix: 1 kg of calcium carbonate powder was placed in a CVD furnace with a median particle size of 10 μm. Nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 850°C at a rate of 5°C / min. Acetylene was introduced at 1 L / min and kept warm for 10 h to uniformly coat the deposited carbon in the calcium carbonate powder. The temperature was then lowered to room temperature. 20 L of 2 mol / L dilute hydrochloric acid was added to the carbon-coated calcium carbonate. The mixture was acid-washed at 80°C for 8 h at 600 r / min in a magnetic stirrer to form pores. The mixture was then washed with water at 80°C for 2 h at 400 r / min until neutral. The mixture was dried at 140°C and sieved through 325 mesh to obtain a porous carbon matrix.

[0089] (2) Silicon deposition: The porous carbon substrate was placed in a CVD furnace and nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 550°C at a rate of 6°C / min, and silane was introduced at a flow rate of 3 L / min. The temperature was kept at this temperature for 6 h to deposit nano-silicon particles on the surface and in the pores of the porous carbon substrate. The temperature was then cooled to room temperature to obtain a silicon-carbon precursor.

[0090] (3) Preparation of silicon-carbon negative electrode material: The silicon-carbon precursor in step (2) is placed in a CVD furnace, and nitrogen is introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed is 1.0 r / min until the oxygen content in the CVD furnace is less than 100 ppm. The temperature is raised to 700°C at a rate of 7°C / min, and acetylene is introduced at 1.5 L / min. The temperature is kept at 700°C for 5 h to uniformly coat the deposited carbon on the surface of the silicon-carbon precursor. The temperature is then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0091] Example 3

[0092] (1) Preparation of porous carbon matrix: 1 kg of magnesium oxide powder was placed in a CVD furnace with a median particle size of 4 μm. Nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 900°C at a rate of 5°C / min. Acetylene was introduced at 0.8 L / min and kept warm for 5 h to uniformly coat the deposited carbon in the magnesium oxide powder. The temperature was then lowered to room temperature. 120 L of 1 mol / L dilute hydrochloric acid was added to the carbon-coated magnesium oxide. The magnesium oxide was acid-washed at 80°C for 15 h at 400 r / min in a magnetic stirrer to form pores. The mixture was washed with water until neutral, dried at 140°C, and sieved through 325 mesh to obtain a porous carbon matrix.

[0093] (2) Silicon deposition: The porous carbon substrate was placed in a CVD furnace, and nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace rotation speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 500°C at a rate of 5°C / min, and silane was introduced at a flow rate of 1 L / min. The temperature was kept for 15 h to deposit nano-silicon on the surface and pores of the porous carbon substrate. The temperature was then lowered to 50°C, and air at a flow rate of 5 L / min and a humidity of 15% was introduced for surface oxidation for 3 h to obtain a silicon-carbon precursor.

[0094] (3) Preparation of silicon-carbon negative electrode material: The silicon-carbon precursor in step (2) is placed in a CVD furnace, nitrogen is introduced until the oxygen content in the CVD furnace is less than 100 ppm, the temperature is raised to 700°C at a rate of 5°C / min, acetylene is introduced at 0.8 L / min, and the temperature is maintained at 700°C for 5 h to uniformly coat the surface and pores of the silicon-carbon precursor with deposited carbon, and the temperature is cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0095] Example 4

[0096] (1) Preparation of porous carbon matrix: 1 kg of magnesium oxide powder was placed in a CVD furnace with a median particle size of 8 μm. Nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 900°C at a rate of 5°C / min. Acetylene was introduced at 5 L / min and kept warm for 5 h to uniformly coat the deposited carbon in the magnesium oxide powder. The temperature was then lowered to room temperature. 100 L of 2 mol / L dilute hydrochloric acid was added to the carbon-coated magnesium oxide. The mixture was acid-washed at 80°C for 15 h at 400 r / min in a magnetic stirrer to form pores. The mixture was washed with water until neutral, dried at 140°C, and sieved through 325 mesh to obtain a porous carbon matrix.

[0097] (2) Silicon deposition: The porous carbon substrate was placed in a CVD furnace, and nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace rotation speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 650°C at a rate of 5°C / min, and silane was introduced at a flow rate of 4 L / min. The temperature was kept for 5 h to deposit nano-silicon on the surface and pores of the porous carbon substrate. The temperature was then lowered to room temperature, and air at a flow rate of 4 L / min and a humidity of 20% was introduced for surface oxidation for 2 h to obtain a silicon-carbon precursor.

[0098] (3) Preparation of silicon-carbon negative electrode material: The silicon-carbon precursor in step (2) is placed in a CVD furnace, and nitrogen is introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed is 1.0 r / min until the oxygen content in the CVD furnace is less than 100 ppm. The temperature is raised to 650°C at a rate of 5°C / min, and acetylene is introduced at 0.8 L / min. The temperature is kept at 650°C for 4 h to uniformly coat the deposited carbon on the surface and pores of the silicon-carbon precursor. The temperature is then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0099] Example 5

[0100] (1) Preparation of porous carbon matrix: 1 kg of magnesium oxide powder was placed in a CVD furnace with a median particle size of 4 μm. Nitrogen was introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 800°C at a rate of 5°C / min. Acetylene was introduced at 1 L / min and kept warm for 6 h to uniformly coat the deposited carbon in the magnesium oxide powder. The temperature was then lowered to room temperature. 100 L of 1 mol / L dilute hydrochloric acid was added to the carbon-coated magnesium oxide. The mixture was acid-washed at 80°C for 24 h at 400 r / min in a magnetic stirrer to form pores. The mixture was washed with water until neutral, dried at 140°C, and sieved through 325 mesh to obtain a porous carbon matrix.

[0101] (2) Silicon deposition: The porous carbon substrate was placed in a CVD furnace and nitrogen was introduced at a nitrogen flow rate of 1 L / min. The pressure in the furnace was maintained at 0.15 MPa and the furnace rotation speed was 1.0 r / min until the oxygen content in the CVD furnace was less than 100 ppm. The temperature was raised to 600 °C at a rate of 5 °C / min, and silane was introduced at a flow rate of 0.3 L / min. The temperature was kept at this temperature for 36 h to deposit nanosilicon on the surface and pores of the porous carbon substrate to obtain a silicon-carbon precursor.

[0102] (3) Preparation of silicon-carbon negative electrode material: The silicon-carbon precursor in step (2) is placed in a CVD furnace, and nitrogen is introduced at a nitrogen flow rate of 1 L / min to maintain the pressure in the furnace at 0.15 MPa. The furnace speed is 1.0 r / min until the oxygen content in the CVD furnace is less than 100 ppm. The temperature is raised to 600°C at a rate of 5°C / min, and acetylene is introduced at 0.8 L / min. The temperature is kept at 600°C for 6 hours to uniformly coat the deposited carbon on the surface and pores of the silicon-carbon precursor. The temperature is then cooled to room temperature to obtain a silicon-carbon negative electrode material.

[0103] Comparative Example 1

[0104] The silicon-carbon negative electrode material was prepared in the manner described in Example 1, except that a commercially available porous carbon matrix was used.

[0105] Comparative Example 2

[0106] A silicon-carbon negative electrode material was prepared in the same manner as described in Example 1, except that a porous carbon matrix was prepared using phenolic resin.

[0107] Comparative Example 3

[0108] A silicon-carbon negative electrode material was prepared in the same manner as described in Example 1, except that a porous carbon matrix prepared from polymethyl methacrylate was used.

[0109] Comparative Example 4

[0110] A silicon-carbon negative electrode material was prepared in the same manner as described in Example 1, except that a porous carbon matrix was prepared using polystyrene resin.

[0111] Comparative Example 5

[0112] A silicon-carbon negative electrode material was prepared in the same manner as described in Example 1, except that a porous carbon matrix was prepared using acrylic resin.

[0113] Test Example 1

[0114] The particle size range of the silicon-carbon anode materials obtained in Examples 1-5 and Comparative Examples 1-5 was measured using a Malvern Mastersizer 3000 laser particle size analyzer. The specific surface area of ​​the silicon-carbon anode materials was measured using a JW-DX dynamic adsorption surface area analyzer. The test results are shown in Table 1.

[0115] Table 1 Particle size and specific surface area of ​​silicon-carbon negative electrode materials obtained in Examples 1 to 5 and Comparative Examples 1 to 5

[0116]

[0117]

[0118] As can be seen from Table 1, the silicon-carbon negative electrode material prepared by the present invention has the characteristics of easy-to-control particle size, moderate median particle size, and small specific surface area, and can reduce the occurrence of side reactions when used in lithium-ion battery systems.

[0119] Test Example 2

[0120] The electrical conductivity, first reversible capacity and first efficiency of the silicon-carbon negative electrode materials obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were tested.

[0121] Lithium battery button test: The silicon-carbon negative electrode materials obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were mixed in pure water at a mass ratio of 96:1:3. The mixture was homogenized to a solid content of 48%. The mixture was coated on a copper foil current collector and vacuum-baked at 100-110°C for 4-8 hours. After compression molding, the negative electrode was punched out. A button-type half-cell was assembled in an argon-filled glove box. The counter electrode was a metal lithium sheet, the separator was PE, and the electrolyte was 1 mol / L LiPF6 in EC / DMC (Vol 1:1). The button-type cell was subjected to charge and discharge tests using the following test procedures: 0.2C DC to 0V, 0.05C DC to 0V, 0V CV 50uA, 0.01C DC to 0V, 0V CV 20uA, Rest 10min, 0.2C CC to 2V. The first reversible capacity and efficiency of the silicon-carbon negative electrode materials in the examples and comparative examples were measured. The button cell testing equipment was the LAND battery testing system of Wuhan Landian Electronics Co., Ltd.

[0122] Conductivity testing: The GEST-126 powder resistivity test was used. Due to the varying density of powder materials, different test pressures yield different data. Therefore, the powder resistivity test for this sample was conducted at a fixed pressure of 5T. The conductivity data was then converted based on the resistivity data. Conductivity and resistivity are inversely proportional: conductivity = 1 / resistivity. The test results are shown in Table 2.

[0123] Table 2 Conductivity, initial reversible capacity and initial efficiency of silicon-carbon negative electrode materials obtained in Examples 1 to 5 and Comparative Examples 1 to 5

[0124]

[0125]

[0126] As shown in Table 2, the silicon-carbon negative electrode material prepared by the present invention has high electrical conductivity and specific capacity. In the lithium-ion battery test system, the first reversible capacity is greater than 2000 mAh / g, and the first coulombic efficiency is greater than 85%.

[0127] The morphology of the porous carbon matrix and silicon-carbon negative electrode material obtained in Example 1 was analyzed using a field emission scanning electron microscope (SEM) (JSM-7800F). Figure 1 and Figure 3 .Depend on Figure 1 and Figure 3 It can be seen that the porous carbon matrix obtained in Example 1 has a rich porous structure, and the surface of the obtained silicon-carbon negative electrode material has a dense carbon coating layer, which can isolate water and electrolyte.

[0128] The material was analyzed by XRD diffractometer (Holland Panalytical X'PERT PRO MPD) to determine the grain size of the material. Figure 4 .Depend on Figure 4 It can be seen that the nano-silicon deposited in Example 1 is amorphous silicon.

[0129] Depend on Figure 5 It can be seen that the silicon-carbon negative electrode material obtained in Example 1 has a relatively high first reversible capacity.

[0130] As can be seen from the above examples, the preparation method of the silicon-carbon negative electrode material provided by the present invention uses metal compound particles as a template, and uses chemical vapor deposition carbon and pickling technology to prepare a porous carbon material as a matrix. It utilizes its advantages such as excellent mechanical properties, good conductivity, stable chemical properties and large pore volume. As a silicon-based material carrier, it can effectively buffer volume expansion, and by chemical vapor deposition of silicon on porous carbon, the particle size of silicon particles can be reduced, and finally a second carbon coating is performed to prepare a silicon-carbon negative electrode material. The porous carbon matrix obtained by the preparation method provided by the present invention has a higher porosity, and the silicon-carbon negative electrode material has a smaller specific surface area and excellent conductivity. It is used in lithium-ion batteries to exhibit superior specific capacity and cycle stability.

[0131] At the same time, when the silicon-carbon negative electrode material provided by the present invention is used as the negative electrode active material of a secondary battery, it can significantly improve the energy density of the battery and has excellent electrochemical and kinetic properties.

[0132] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The steps are: A metal compound is first carbon-coated by chemical vapor deposition to obtain a porous carbon matrix precursor; the metal compound comprises one or more of potassium oxide, calcium oxide, magnesium oxide, aluminum oxide, zinc oxide, sodium carbonate, magnesium carbonate, and calcium carbonate; the median particle size of the metal compound is 1 to 10 μm; and the mass ratio of the metal compound to carbon in the porous carbon matrix precursor is 1:1 to 5; The carbon source used in the first carbon coating includes one or more of methane, ethane, propane, ethylene and acetylene; the gas flow rate of the carbon source is 0.1 to 5 L / min; the temperature of the first carbon coating is 700 to 900° C., and the time is 0.5 to 12 hours; the first carbon coating is carried out in an inert gas; acid-washing the porous carbon matrix precursor to obtain a porous carbon matrix; the porous carbon matrix has a porosity greater than 50% and an average pore size of 10 to 100 nm; The porous carbon matrix is ​​subjected to silicon deposition by chemical vapor deposition to obtain a silicon-carbon precursor; the silicon source used in the silicon deposition includes one or more of monosilane, dimethylsilane, chlorosilane, chloromethylsilane and dichlorosilane; the gas flow rate of the silicon source is 0.3 to 2 L / min; the temperature of the silicon deposition is 400 to 700° C., and the time is 0.5 to 24 hours; the silicon deposition is carried out in an inert gas; The silicon-carbon precursor is subjected to a second carbon coating by cracking an organic carbon source to obtain the silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that The acid used in the pickling is one or more of dilute hydrochloric acid, dilute sulfuric acid and dilute nitric acid; The concentration of the acid is 0.5 to 5 mol / L; the molar ratio of the acid to the metal compound is greater than 1.2:1; The pickling time is 1 to 12 hours, and the temperature is 25 to 100°C.

3. The preparation method according to claim 1, characterized in that The organic carbon source used in the second carbon coating includes one or more of methane, acetylene, toluene, glucose, petroleum asphalt, mesophase asphalt, phenolic resin and polyacrylonitrile; The temperature of the second carbon coating is 300-900° C., and the time is 0.5-12 hours; the second carbon coating is performed in an inert gas.

4. The silicon-carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 3, characterized in that: The silicon-carbon negative electrode material is a core-shell structure; The core of the core-shell structure includes a porous carbon matrix and nano-silicon particles; the nano-silicon particles are distributed in the pores and surface of the porous carbon matrix; The shell of the core-shell structure is a carbon coating layer.

5. The silicon-carbon negative electrode material according to claim 4, characterized in that The specific surface area of ​​the silicon-carbon negative electrode material is 1 to 10 m 2 / g, median particle size is 3-20 μm; The mass percentage of silicon element in the silicon-carbon negative electrode material is 25-75%, and the mass percentage of carbon element is 25-75%.

6. The silicon-carbon negative electrode material according to claim 4 or 5, characterized in that: The nano-silicon particles include amorphous silicon and / or crystalline silicon; the median particle size of the nano-silicon particles is less than 50 nm; The mass percentage of the carbon coating layer in the silicon-carbon negative electrode material is 1-10%.

7. Use of the silicon-carbon negative electrode material according to any one of claims 4 to 6 in lithium-ion batteries.

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