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

Abstract

The application relates to a silicon-carbon negative electrode material and a preparation method thereof and a lithium ion battery. The preparation method of the silicon-carbon negative electrode material comprises the following steps: S1. preparation of a porous carbon@metal coating layer: adopting an atomic layer deposition process, depositing metal on the surface and inside pores of porous carbon to obtain a porous carbon@metal coating layer; S2. silane deposition: performing silane deposition on the porous carbon@metal coating layer; and S3. high-temperature coating: in the presence of a carbon source gas, performing heat treatment to obtain the silicon-carbon negative electrode material. The porous carbon surface in the silicon-carbon negative electrode material obtained by the application has a uniformly-distributed high-temperature-resistant coating layer, can effectively isolate the direct contact between the porous carbon and silicon, improves the quality of the coating carbon layer, and thus has better cycle and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a silicon-carbon anode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the increasing prominence of energy crises and environmental problems in today's society, new clean energy sources and energy storage have become research hotspots. Chemical energy storage technology, with its advantages of being unrestricted by geographical location, flexible construction, and adjustable capacity, has promising development prospects. Among them, lithium-ion batteries, due to their high energy density, high power density, long lifespan, and environmental friendliness, have broad application prospects in portable consumer electronics, electric vehicles, large-scale energy storage devices, and distributed mobile power supplies. With the Ministry of Industry and Information Technology and other ministries requiring power battery cells to reach a specific energy of 300Wh / kg, and the rapidly increasing demand for battery energy density in other fields, the development of higher energy density lithium-ion batteries is particularly urgent. Currently, graphite is the main anode material for lithium batteries. Although it has advantages in high conductivity and stability, its energy density development has approached its theoretical maximum of 372mAh / g, which cannot meet the market's ever-increasing demand for energy density. Finding a new high-capacity, safe, and long-cycle-capacity material to replace graphite-based anode materials has become key to the further development of power lithium-ion batteries. Silicon has a theoretical capacity as high as 4200 mAh / g, showing great development potential.

[0003] Silicon possesses ultra-high specific capacity and low lithium intercalation potential, but in practical battery applications, silicon materials still face pressing problems. This is because during charging and discharging, the silicon material undergoes a huge volume change, approaching 300%, accompanied by the intercalation and deintercalation of lithium ions. This causes repeated formation of the SEI film and material detachment from the current collector, leading to a continuous increase in polarization, resulting in a significant decrease in battery capacity and poor cycle stability. The patent "Group14 composite (WO2023091195A2)" uses porous carbon as a matrix and prepares a novel silicon-carbon material through silane deposition technology. The porous carbon matrix can alleviate the volume expansion of silicon, achieving a capacity of over 1800 mAh / g and an initial efficiency greater than 90%. The patent "A low-expansion, long-life silicon-carbon composite material and its preparation method (CN115911326A)" uses a uniform mixture of porous carbon and porous metal oxides to obtain a carbon-based composite precursor. Nano-silicon is then deposited in the precursor via silane pyrolysis, and finally, nitrogen-doped amorphous carbon is deposited on it via plasma deposition to obtain the silicon-carbon composite material.

[0004] Existing novel silicon-carbon anode materials typically employ the following fabrication process: porous carbon matrix – silane deposition – low-temperature acetylene coating. Since the silicon formed by silane deposition is mostly amorphous silicon with high reactivity, it will spontaneously combust upon direct contact with air without coating. Therefore, coating is necessary to isolate it from air and water. Currently, the commonly used coating method is low-temperature CVD acetylene coating, but this process suffers from low acetylene carbonization efficiency and poor carbon layer quality. Furthermore, if the temperature increases during coating, amorphous silicon is prone to crystallization transformation. Because amorphous silicon is in direct contact with porous carbon, they easily react at higher temperatures to form silicon carbide, leading not only to a significant reduction in material capacity but also exacerbating volume expansion and severely affecting the electrode's cycle stability. Therefore, while achieving high specific capacity, existing silicon-carbon anode materials still face challenges such as limited coating processes, low capacity retention, and insufficient cycle life. Summary of the Invention

[0005] The technical problem this invention aims to solve is the issue that silicon in existing silicon-carbon anode materials exhibits large volume expansion and poor cycle stability during charge and discharge, and that silicon reacts with carbon to form silicon carbide during high-temperature coating, leading to rapid capacity decay. This invention provides a silicon-carbon anode material, its preparation method, and a lithium-ion battery. By coating the surface of porous carbon, this invention effectively isolates the direct contact between the porous carbon and silicon. Then, after silane deposition, high-temperature coating is performed to obtain an effective coating layer, resulting in a high-performance novel silicon-carbon anode material.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] This invention provides a method for preparing a silicon-carbon anode material, comprising the following steps: S1. Preparation of porous carbon@metal coating: Metal is deposited on the surface and inside the pores of porous carbon using atomic layer deposition (ALD) to obtain porous carbon@metal coating; S2. Silane deposition: Silane deposition is performed on the porous carbon@metal coating layer; S3. High-temperature coating: The silicon-carbon anode material is obtained by heat treatment in the presence of carbon source gas.

[0008] This invention does not limit the pore volume, the ratio of micropores to mesopores, or the type of carbon matrix of the porous carbon, as long as the technical effects of this invention can be achieved.

[0009] In this invention, micropores generally refer to pore structures with a pore size of less than 2 nm, while mesopores generally refer to pore structures with a pore size between 2 nm and 50 nm.

[0010] In this invention, the carbon matrix type of the porous carbon can be conventional in the art, such as biomass matrix, lignin matrix, resin matrix, petroleum coke matrix or coal matrix; wherein, the source of the biomass matrix can be conventional in the art, such as coconut shell, straw, bamboo or wood.

[0011] In this invention, the porous carbon can be prepared by the following method: carbonizing and activating a carbon matrix at a carbonization temperature of 400-600℃ and an activation temperature of 800-1000℃. The activation method can be conventional in the art, such as carbon dioxide activation, water activation, or alkali activation.

[0012] In a preferred embodiment, the porous carbon has a pore volume of 0.8 cm³. 3 / g, with a microporous content of 90%, a mesoporous content of 10%, a pore size of 1-50 nm, and a carbon matrix type of biomass matrix.

[0013] In this invention, in step S1, the metal source precursor used in the atomic layer deposition process preferably includes metal chlorides and / or metal hydrides.

[0014] The metal chloride preferably includes one or more of AlCl3, TiCl4 and CuCl2.

[0015] The metal hydride preferably includes one or more of AlH3 and GeH4.

[0016] In this invention, in step S1, the reaction temperature for atomic layer deposition is preferably 50-200°C, more preferably 50-150°C, for example 100°C.

[0017] In this invention, in step S1, the reaction chamber pressure of the atomic layer deposition is preferably maintained at 0.1 Torr-30 Torr, more preferably 5 Torr-15 Torr, for example 1 Torr or 10 Torr.

[0018] In this invention, in step S1, nitrogen gas can be used to carry or purge the metal source precursor during the atomic layer deposition process.

[0019] The flow rate of nitrogen is preferably 2-50 sccm, more preferably 20-40 sccm, for example 5 sccm or 30 sccm.

[0020] In this invention, in step S1, the atomic layer deposition cycle can be 1-50 times, preferably 5-30 times, and more preferably 10-20 times.

[0021] In this invention, step S1 may further include an oxidant reaction step after the atomic layer deposition process.

[0022] The oxidant can be conventional in the art, and is preferably one or more of hydrogen peroxide, nitric acid, sulfuric acid and potassium permanganate, such as hydrogen peroxide.

[0023] When the oxidant is hydrogen peroxide, the concentration of hydrogen peroxide in the reaction is preferably 1-25 mol / L, more preferably 10-20 mol / L, for example 1 mol / L, 10 mol / L or 20 mol / L.

[0024] The reaction time is preferably 20-100 min, more preferably 30-90 min, for example 30 min, 60 min or 90 min.

[0025] In this invention, in step S1, the metal element in the metal cladding layer may include one or more of Al, Ti, Ge and Cu.

[0026] In this invention, in step S1, the metal cladding layer may be a single metal layer and / or a metal oxide layer.

[0027] In this invention, in step S1, the thickness of the metal cladding layer is preferably 0.5-50 nm, more preferably 0.5-15 nm, for example 0.5 nm, 5 nm or 15 nm.

[0028] In this invention, in step S1, the metal coating layer can be uniformly coated on the surface and inside the pores of porous carbon.

[0029] In this invention, the silane deposition process in step S2 can be a conventional process in the art. For example, the silane deposition can be performed using chemical vapor deposition (CVD).

[0030] In this invention, in step S2, the silane deposition can be carried out in a fluidized bed reactor.

[0031] In this invention, in step S2, the silane deposition can be carried out under an inert gas atmosphere, preferably nitrogen.

[0032] When the inert gas is nitrogen, the flow rate of the nitrogen is preferably 20-60 L / min, for example, 40 L / min.

[0033] In this invention, in step S2, the heat treatment temperature for silane deposition is preferably 450-600℃, more preferably 500-550℃.

[0034] In this invention, in step S2, the preferred flow rate of the silane is 5-20 L / min, for example, 10 L / min.

[0035] In this invention, in step S2, the heat treatment time for the silane deposition is preferably 2-10 h, more preferably 5-8 h, for example 6.5 h.

[0036] In this invention, in step S3, the carbon source gas preferably includes one or more of acetylene, methane, propane, and octane, for example, acetylene or a mixture of methane and acetylene.

[0037] In this invention, in step S3, the heat treatment temperature can be 500-1000℃, preferably 600-900℃, more preferably 650-750℃, for example 500℃, 700℃ or 1000℃.

[0038] In this invention, in step S3, the heat treatment time can be 2-10 hours, preferably 3-8 hours, more preferably 3-5 hours, for example 2 hours, 4 hours or 10 hours.

[0039] The present invention also provides a silicon-carbon anode material, which is prepared according to the preparation method of silicon-carbon anode material described above.

[0040] The present invention also provides a silicon-carbon anode material, comprising a porous carbon matrix, a metal coating layer, an amorphous silicon layer, and a carbon coating layer; the metal coating layer is located on the surface of the porous carbon matrix, the amorphous silicon layer is located on the surface of the metal coating layer, and the carbon coating layer is located on the surface of the amorphous silicon layer; the thickness of the metal coating layer is 0.5-50 nm.

[0041] In this invention, the surface of the porous carbon matrix generally includes the outer surface of the porous carbon matrix and the inner surface of the pore channels.

[0042] In this invention, the thickness of the metal cladding layer can be 0.5-15 nm, for example 0.5 nm, 5 nm or 15 nm.

[0043] In this invention, the metal element in the metal cladding layer may include one or more of Al, Ti, Ge and Cu; In this invention, the metal cladding layer may be a single metal layer and / or a metal oxide layer; In this invention, the metal coating layer can uniformly coat the surface and pores of the porous carbon.

[0044] The present invention also provides a lithium-ion battery comprising the silicon-carbon anode material as described above.

[0045] The process flow of this invention is as follows: porous carbon matrix—ALD deposition—silane deposition—high-temperature carbon source coating. Before silane deposition, a uniform, nanoscale coating layer with controllable thickness can be formed on the surface and inside the pores of the porous carbon framework using ALD technology. This coating layer serves two purposes: firstly, it isolates the porous carbon from direct contact with silicon, which is beneficial for subsequent high-temperature coating; secondly, it also has electrical and ion-conducting properties, which can effectively improve the fast-charging performance of the material.

[0046] To achieve the above objectives, the present invention mainly employs the following technical means: 1. Atomic layer deposition (ALD) technology can be used to form a high-temperature resistant coating layer on the inner surface of porous carbon. This method can effectively increase the coating temperature, thereby improving the quality of the coated carbon layer and solving the problem of poor quality coated carbon layers caused by low coating temperatures.

[0047] 2. After the high-temperature resistant coating layer is formed, silane deposition can be performed. This method avoids the long time required by traditional silane deposition technology, thereby improving production efficiency and reducing production costs.

[0048] 3. After silane deposition, a high-temperature coating can be performed again to further improve the quality of the coated carbon layer. This method can effectively solve the problem of low silane utilization, which leads to a large amount of silane waste and increased production costs.

[0049] 4. Throughout the process, by precisely controlling the parameters of each step, such as temperature, pressure, and time, the utilization rate of silane can be further improved, silane waste can be reduced, and production costs can be lowered.

[0050] 5. The matrix is ​​reinforced, making it more suitable for experiments in high-pressure real-world scenarios.

[0051] Without violating common sense in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0052] The reagents and raw materials used in this invention are all commercially available.

[0053] The positive and progressive effects of this invention are as follows: 1. Improved Coating Quality: This invention increases the heat treatment temperature for coating, enabling the formation of a high-temperature resistant coating layer on the inner surface of porous carbon using ALD technology. This is followed by silane deposition and high-temperature coating to obtain a high-quality coated carbon layer. Compared to existing technologies, this method effectively improves the quality of the coated carbon layer, thereby enhancing the electrochemical performance of silicon-carbon anode materials.

[0054] 2. Improved production efficiency: This invention uses ALD technology to form a high-temperature resistant coating layer. Compared with existing silane deposition technology, this method can form a high-quality coating layer in a short time, thereby greatly improving production efficiency and reducing production costs.

[0055] 3. Improve silane utilization: This invention improves silane deposition technology, which can effectively increase the utilization rate of silane, reduce silane waste, and further reduce production costs.

[0056] 4. Optimize battery performance: Since the present invention can obtain a high-quality coated carbon layer, the silicon-carbon anode material prepared by this method has better cycle and rate performance, which can optimize the overall performance of the battery. Attached Figure Description

[0057] Figure 1 This is a transmission electron microscope (TEM) image of PC@Al2O3 in Example 3.

[0058] Figure 2 This is a transmission electron microscope (TEM) image of Si-C@Al2O3@C in Example 12.

[0059] Figure 3 The image shows the X-ray diffraction (XRD) pattern of Si-C@Al2O3@C in Example 1.

[0060] Figure 4 The image shows the X-ray diffraction (XRD) pattern of Si-C@C in Comparative Example 1.

[0061] Figure 5 This is a schematic diagram of the structure of Si-C@Al2O3@C in Example 1. Detailed Implementation

[0062] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0063] The porous carbon matrix used in the following examples and comparative examples is a biomass matrix with a pore volume of 0.8 cm³. 3 / g, with a microporous content of 90%, a mesoporous content of 10%, and a pore size of 1-50nm.

[0064] Preparation method of porous carbon: Taking coconut shell as a biomass matrix as an example, carbonization is first carried out at a temperature of 400-600℃. Then, activation is performed. During activation, water vapor is introduced, and the reaction takes place at 800-1000℃. Water reacts with the porous carbon, etching out pores. Finally, porous carbon is formed.

[0065] Example 1

[0066] S1. Preparation of porous carbon@metal layer

[0067] Porous carbon powder was placed in a container and then transferred to an ALD chamber. The chamber was evacuated and purged with nitrogen three times. The chamber was heated to 100°C and maintained at a pressure of 10 torr. Nitrogen was then introduced into the chamber to ensure thorough mixing of the porous carbon. AlCl3 was then pulsed into the chamber with N2 at a flow rate of 30 sccm, adsorbing onto the porous carbon matrix powder. The pulse duration was 100 s. The remaining AlCl3 was then removed by rinsing with N2 at a flow rate of 30 sccm for 60 s, completing one ALD deposition cycle. By controlling the number of repetitions, different coating thicknesses were obtained, denoted as PC@Al, and 10 ALD deposition cycles were performed.

[0068] S2. Oxidation

[0069] The PC@Al obtained from S1 was placed in a 10 mol / L hydrogen peroxide solution and stirred for 60 min to oxidize it, yielding PC@Al2O3.

[0070] S3. Silane deposition

[0071] The PC@Al2O3 obtained from S2 was placed in a fluidized bed reactor and heated to 500°C under a nitrogen atmosphere (flow rate 40 L / min). Silane was then introduced at a flow rate of 10 L / min. The reaction temperature was 550°C, and the holding time was 6.5 h. This method is a conventional process.

[0072] S4. High-temperature coating

[0073] The silane deposit obtained from S3 was transferred to a fluidized bed apparatus, and a carbon-containing atmosphere of acetylene (but not limited to methane, propane, octane, mixed carbon sources, etc.) was introduced at a flow rate of 5 L / min. Then, the material was coated at a high temperature: 700℃ for 4 h to obtain the Si-C@Al2O3@C product.

[0074] Example 2

[0075] The preparation method of Example 2 is the same as that of Example 1, except that the number of ALD deposition cycles in S1 is 1.

[0076] Example 3

[0077] The preparation method of Example 3 is the same as that of Example 1, except that the number of ALD deposition cycles in S1 is 20.

[0078] Example 4

[0079] The preparation method of Example 4 is the same as that of Example 1, except that the concentration of hydrogen peroxide in S2 is 1 mol / L.

[0080] Example 5

[0081] The preparation method of Example 5 is the same as that of Example 1, except that the concentration of hydrogen peroxide in S2 is 20 mol / L.

[0082] Example 6

[0083] The preparation method of Example 6 is the same as that of Example 1, except that the stirring time in S2 is 30 min.

[0084] Example 7

[0085] The preparation method of Example 7 is the same as that of Example 1, except that the stirring time in S2 is 90 min.

[0086] Example 8

[0087] The preparation method of Example 8 is the same as that of Example 1, except that the heat treatment temperature in S4 is 500°C.

[0088] Example 9

[0089] The preparation method of Example 9 is the same as that of Example 1, except that the heat treatment temperature in S4 is 1000℃.

[0090] Example 10

[0091] The preparation method of Example 10 is the same as that of Example 1, except that the heat treatment time in S4 is 2 hours.

[0092] Example 11

[0093] The preparation method of Example 11 is the same as that of Example 1, except that the heat treatment time in S4 is 10h.

[0094] Example 12

[0095] The preparation method of Example 12 is the same as that of Example 1, except that the coating gas source in S4 is a methane / acetylene mixture.

[0096] Example 13

[0097] The preparation method of Example 13 is the same as that of Example 1. The only difference between Example 13 and Example 1 is that an Al-Ti mixed layer is sputtered on the surface of porous carbon. The preparation process of the porous carbon@metal layer in Example 13 is as follows.

[0098] 1. Porous carbon matrix powder is placed in a container and then transferred to an ALD chamber. The chamber is evacuated and purged with nitrogen three times. The reaction chamber is heated to 100°C and maintained at a pressure of 10 torr. Nitrogen gas is then introduced into the chamber to ensure thorough mixing of the porous carbon. The AlCl3 precursor is then pulsed into the reaction chamber with N2 at a flow rate of 30 sccm, adsorbing onto the porous carbon matrix powder. The pulse duration is 100 s. The remaining AlCl3 is then removed by rinsing with N2 at a flow rate of 30 sccm for 60 s, completing one ALD deposition cycle. After five cycles, porous carbon@Al is obtained. 2. Nitrogen gas is introduced into the chamber to ensure thorough mixing of porous carbon@Al within the chamber. Then, the TiCl4 precursor is pulsed into the reaction chamber under a flow rate of 30 sccm N2, adsorbing onto the porous carbon matrix powder. The pulse duration is 100 s. The chamber is then purged with 30 sccm N2 to remove the remaining TiCl4 for 60 s, thus completing one ALD deposition cycle. After five cycles, an Al-Ti deposition layer is finally obtained.

[0099] Example 14

[0100] The preparation method of Example 14 is the same as that of Example 13. The only difference between Example 14 and Example 13 is that a Ti-Ge deposition layer is sputtered onto the surface of porous carbon.

[0101] Example 15

[0102] The preparation method of Example 15 is the same as that of Example 13. The only difference between Example 15 and Example 13 is that an Al-Cu deposition layer is sputtered onto the surface of porous carbon.

[0103] Example 16

[0104] The preparation method of Example 16 is the same as that of Example 1, except that the pressure in the reaction chamber in S1 is maintained at 30 torr.

[0105] Example 17

[0106] The preparation method of Example 17 is the same as that of Example 1, except that the pressure in the reaction chamber in S1 is maintained at 1 torr.

[0107] Example 18

[0108] The preparation method of Example 18 is the same as that of Example 1, except that the flow rate of N2 in S1 is 50 sccm.

[0109] Example 19

[0110] The preparation method of Example 19 is the same as that of Example 1, except that the flow rate of N2 in S1 is 5 sccm.

[0111] Comparative Example 1

[0112] S1. Silane deposition

[0113] Porous carbon (PC) was placed in a fluidized bed reactor and heated to 500°C in a nitrogen atmosphere (flow rate 40 L / min). Silane was then introduced at a flow rate of 10 L / min, and the reaction was maintained at 550°C for 6.5 h. This method is a conventional process.

[0114] S2. High-temperature coating

[0115] The silane deposit obtained from S2 is transferred to a fluidized bed apparatus, and a carbon-containing atmosphere of acetylene is introduced, but not limited to methane, propane, octane, mixed carbon sources, etc., and then coated at high temperature. The heat treatment temperature is 700℃ and the heat treatment time is 4h to obtain Si-C@C product.

[0116] Comparative Example 2

[0117] S1. Silane deposition

[0118] Porous carbon (PC) was immersed in a liquid Al(NO)3 solution, and the supernatant was removed. The lower solid layer was then heat-treated to obtain Al2O3-coated porous carbon. This carbon was then placed in a fluidized bed reactor and heated to 500°C under a nitrogen atmosphere (40 L / min). Silane was introduced at a flow rate of 10 L / min, and the reaction was maintained at 550°C for 6.5 h. This method is a conventional process.

[0119] S2. High-temperature coating

[0120] The silane deposit obtained from S2 is transferred to a fluidized bed apparatus, and a carbon-containing atmosphere of acetylene is introduced, but not limited to methane, propane, octane, mixed carbon sources, etc., and then coated at high temperature. The heat treatment temperature is 700℃ and the heat treatment time is 4h to obtain the Si-C@Al2O3@C product.

[0121] Effect Example

[0122] 1. TEM Analysis: The PC@Al2O3 samples prepared in Examples 1-3 were placed in the sample chamber of a dual-beam electron microscope (DEM), and then a cross-section was obtained using Ga ion cutting. The thickness of the metal coating layer was then measured at high magnification in TEM mode. The TEM image of PC@Al2O3 in Example 3 is shown below. Figure 1 As shown, the thickness of the metal coating on the surface is approximately 15 nm. Figure 5A schematic diagram of the structure of Si-C@Al2O3@C in Example 1 is given, where the width of the red line represents the thickness of the metal coating layer in Example 1.

[0123] TEM image of Si-C@Al2O3@C prepared in Example 12 is shown below. Figure 2 As shown, a distinct carbon layer can be observed on the surface of silicon-carbon materials, and there are two types of carbon layers.

[0124] 2. XRD Analysis: The XRD pattern of Si-C@Al2O3@C obtained in Example 1 is as follows. Figure 3 As shown, the XRD pattern of Si-C@C prepared in Comparative Example 1 is as follows. Figure 4 As shown, it can be seen that in Example 1, when there is an oxide layer for isolation, silicon exists in the form of amorphous silicon, while in Comparative Example 1, obvious silicon carbide peaks are observed. When the surface is coated at high temperature, silicon and carbon matrix react to form silicon carbide.

[0125] 3. Silicon Content: The obtained Si-C@Al2O3@C was immersed in a dilute hydrochloric acid solution for etching to remove the coating oxide layer. After drying, the mass of Si-C@C (M1) was obtained. Then, it was placed in a muffle furnace and heat-treated at 1000℃ in air to obtain white silicon oxide, weighed as M2. The silicon content was calculated using the following formula: Silicon content = M2 / 60.09 28.09 / M1 100%. 60.09 is the molar mass of silicon dioxide, and 28.09 is the molar mass of silicon.

[0126] 4. Porous Carbon Crushing Force: The obtained Si-C@Al2O3@C sample was dispersed in an ethanol dispersion, and then spherical or regularly shaped particles of 5-10 μm were selected. Pressure was continuously applied to the particles until they broke. The vector curve of pressure and displacement was obtained, and the pressure at the instant of compression was the crushing force.

[0127] 5. Electrochemical performance tests were conducted on the negative electrode materials prepared in Examples 1-13 and Comparative Examples 1-3. The testing system used in the electrochemical performance tests was purchased from Wuhan Landian Electronics Co., Ltd., model CT2001A, serial number 20170512000.

[0128] Test methods for electrochemical performance testing: Battery fabrication: The negative electrode materials prepared in Examples 1-12 and Comparative Examples 1-3 were mixed with binder LA132 and conductive agent SuperP in a mass ratio of 70:20:10 to prepare a slurry. The slurry was homogenized and coated onto copper foil, then vacuum dried and rolled to obtain the negative electrode sheet. A 1 mol / L LiPF6 electrolyte (solvents being ethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1), a polypropylene microporous membrane as the separator, and a lithium metal sheet as the counter electrode were assembled into a coin cell in an argon-filled inert gas glove box system to obtain a lithium-ion battery.

[0129] (1) Initial charge and discharge capacity, first efficiency and voltage drop

[0130] The lithium-ion batteries prepared above were charged and discharged at a voltage of 0.01-1.5 V and a current density of 0.1 A / g to obtain the initial charge capacity and initial discharge capacity. The ratio of initial charge capacity to initial discharge capacity was then used. 100% effective on the first try.

[0131] Pressure loss = First effect under no compaction - First effect under compaction 1.1 g / cm³

[0132] (2) Capacity retention rate after 400 cycles

[0133] The lithium-ion battery prepared above was subjected to three charge-discharge cycles at a voltage of 0.01-1.5 V and a current density of 0.1 A / g. Then, it was subjected to charge-discharge cycle tests at a current density of 1 A / g. The capacity retention rate was obtained after 400 cycles.

[0134] (3) Expansion rate

[0135] The initial thickness of the negative electrode sheet prepared above was tested. The prepared lithium-ion battery was subjected to a discharge-charge-discharge test (1.5 weeks) at a voltage of 0.01-1.5 V and a current density of 0.1 A / g. Then, the battery was disassembled, and the final thickness of the negative electrode sheet was measured. The expansion rate was calculated using the following formula: Expansion rate = (Final thickness - Initial thickness) / Initial thickness 100%.

[0136] (4) 4C discharge retention rate

[0137] The lithium-ion batteries prepared above were subjected to 10 cycles at voltages of 0.01-1.5 V and current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, and 4C. The retention rate at different current densities was then obtained with the first cycle at 0.1C as 100%.

[0138] (5) Powder resistivity

[0139] The silicon-carbon anode materials prepared in the examples and comparative examples were poured into a mold and pressed into small discs under a pressure of 20 MPa. The current and voltage of the samples were then tested using the four-probe method, and the resistivity was calculated.

[0140] As shown in Table 1 below, comparing Examples 1-3 and Comparative Example 1, it can be found that with the increase of deposition times, the coating layer formed on the inner surface becomes thicker, and the compressive strength of the porous carbon is higher, indicating that the strength of the porous carbon particles is higher, and its heat resistance increases accordingly. However, this leads to a reduction in pore size, ultimately reducing the amount of silicon deposited and causing a decrease in capacity. However, without ALD deposition, when coated at 700℃, the deposited amorphous silicon reacts with the porous carbon to form silicon carbide, resulting in a sharp decrease in capacity. Moreover, in the first deposition, the metal layer is very thin, and its high-temperature resistance is not significant. During high-temperature coating, a small amount of amorphous silicon also reacts with carbon to form silicon carbide.

[0141] Table 1. Effect of different deposition times on performance

[0142] As shown in Table 2, comparing Examples 1 and 4-7, it was found that with increasing hydrogen peroxide solution concentration and longer oxidation time, the oxidation effect was better, completely converting Al into an alumina coating. Since alumina has a higher melting point than Al, its heat resistance is better. However, excessively high concentrations slow down the oxidation efficiency. The metal oxide coating layer has little impact on the final coating temperature because the oxide layer is sufficiently intact, and subsequent carbon coating will not result in a melting state. If the oxidation degree is low, part of the coating layer still exists in the form of Al. During subsequent high-temperature carbon coating, this coating layer will melt, causing silicon, Al, and the carbon matrix to react and generate Al. x The presence of Si alloy phases and SiC leads to reduced capacity and initial efficiency. Although prolonged stirring can completely oxidize Al to alumina, subsequent washing to remove hydrogen peroxide causes the porous carbon matrix to form more oxygen-containing functional groups, resulting in reduced initial efficiency.

[0143] Table 2. Effect of different oxidation degrees on performance

[0144] As shown in Table 3, comparing Examples 1 and 8-11, it was found that with increasing coating temperature and time, the acetylene cracking efficiency is higher, resulting in a higher quality coating layer with better conductivity and significantly improved rate performance. However, excessively high temperatures can cause amorphous silicon to transform into monocrystalline silicon. Monocrystalline silicon expands anisotropically, with greater expansion at different crystal orientations, while amorphous silicon expands isotropically, i.e., uniformly. Therefore, excessively high temperatures and prolonged periods can lead to increased expansion and decreased cycle performance.

[0145] Table 3. Effects of different heat treatment conditions on performance

[0146] As shown in Table 4 below, a comparison of Examples 1 and 12 reveals that coating can also be achieved using a mixed gas source, and different gas sources result in different carbon layers, leading to significant differences in the final cycle capacity retention rate.

[0147] Table 4. Effects of different gas sources on performance

[0148] As shown in Table 5 below, comparing Example 1, Comparative Example 2, and Example 13, it was found that under the same deposition process, due to the larger diameter of the liquid phase molecules during the liquid phase coating process, the pores are blocked, resulting in more closed pores inside. Under the same silane deposition process, the pore volume is smaller, and the silane quickly fills the pores, causing subsequent silane to be deposited on the outer surface of the porous carbon, forming floating silicon on the surface, which increases powder resistance and increases gas generation in the slurry. However, due to the presence of closed pores inside, the surface of the uncoated material is not as dense and uniform as that of the vapor phase coated material, and its pressure resistance is also slightly worse than that of the vapor phase coated material. The multi-layer coating can form both fast ion conductors and highly conductive coatings, so compared to the single-layer coating in Example 1, the rate performance of Example 13 is better.

[0149] Table 5. Effects of liquid phase coating and multilayer coating on performance

[0150] As shown in Table 6, comparing Examples 1 and 16-19, it was found that under high deposition pressure, the coated metal layer rapidly nucleates and grows, causing it to clog pores, especially micropores. This ultimately leads to a reduction in overall pore volume. Under similar silicon deposition processes, after the silicon fills the pores, it will further deposit on the surface, eventually forming a silicon shell layer. In subsequent high-temperature coating, this silicon will react with acetylene to generate a mixed SiC / Si / C coating layer, resulting in reduced capacity and initial efficiency. Moreover, a large amount of gas will be generated during subsequent cell fabrication, affecting the slurry preparation process. However, when the deposition pressure or nitrogen flow rate is too low, the effect of complete deposition into the pores is better, and the deposition layer is more uniform, but the process time is too long and the efficiency is low. However, when the nitrogen flow rate is too high, the metal precursor is blown away before it is adsorbed, causing the formed metal layer to be discontinuous or broken. This ultimately leads to the reaction of the amorphous silicon deposited during high-temperature coating with carbon to form silicon carbide, resulting in a significant reduction in capacity and initial efficiency.

[0151] Table 6. Effects of different sedimentation conditions on performance

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, It includes the following steps: S1. Preparation of porous carbon@metal coating: Metal is deposited on the surface and inside the pores of porous carbon using atomic layer deposition process to obtain porous carbon@metal coating; S2. Silane deposition: Silane deposition is performed on the porous carbon@metal coating layer; S3. High-temperature coating: The silicon-carbon anode material is obtained by heat treatment in the presence of carbon source gas.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, It meets one or more of the following conditions: (1) In step S1, the carbon matrix of the porous carbon is a biomass matrix, lignin matrix, resin matrix, petroleum coke matrix or coal matrix, and the source of the biomass matrix preferably includes one or more of coconut shell, straw, bamboo and wood. (2) In step S1, the porous carbon is prepared by the following method: carbonizing and activating the carbon matrix, wherein the carbonization temperature is preferably 400-600℃, the activation temperature is preferably 800-1000℃, and the activation method is preferably carbon dioxide activation, water activation or alkali activation. (3) In step S1, the pore volume of the porous carbon is 0.2-2 cm³. 3 / g, for example 0.8 cm 3 / g; (4) In step S1, the micropores in the porous carbon account for 80-95%, for example 90%, and the remainder are mesopores; (5) In step S1, the pore size of the porous carbon is 1-50 nm.

3. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, It meets one or more of the following conditions: (1) In step S1, the metal source precursor used in the atomic layer deposition process includes metal chlorides and / or metal hydrides; the metal chlorides preferably include one or more of AlCl3, TiCl4 and CuCl2; the metal hydrides preferably include one or more of AlH3 and GeH4; (2) In step S1, the reaction temperature of the atomic layer deposition is 50-200℃, preferably 50-150℃, for example 100℃; (3) In step S1, the reaction chamber pressure of the atomic layer deposition is maintained at 0.1 Torr-30 Torr, preferably 5 Torr-15 Torr, for example 1 Torr or 10 Torr; (4) In step S1, nitrogen is used to carry or purge the metal source precursor in the atomic layer deposition process; the flow rate of the nitrogen is preferably 2-50 sccm, more preferably 20-40 sccm, for example 5 sccm or 30 sccm; (5) In step S1, the atomic layer deposition cycle number is 1-50 times, preferably 5-30 times, and more preferably 10-20 times.

4. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In step S1, the atomic layer deposition process is followed by a step of adding an oxidant reaction.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, (1) The oxidant is one or more of hydrogen peroxide, nitric acid, sulfuric acid, and potassium permanganate, for example, hydrogen peroxide; when the oxidant is hydrogen peroxide, the concentration of hydrogen peroxide in the reaction is preferably 1-25 mol / L, more preferably 10-20 mol / L, for example 1 mol / L, 10 mol / L, or 20 mol / L; and / or, (2) The reaction time is 20-100 min, preferably 30-90 min, for example 30 min, 60 min or 90 min.

6. The method for preparing the silicon-carbon anode material according to any one of claims 1-5, characterized in that, It meets one or more of the following conditions: (1) In step S1, the metal elements in the metal cladding layer include one or more of Al, Ti, Ge and Cu; (1) In step S1, the metal cladding layer is a single metal layer and / or a metal oxide layer; (2) In step S1, the thickness of the metal coating layer is 0.5-50 nm, preferably 0.5-15 nm, for example 0.5 nm, 5 nm or 15 nm; (3) In step S1, the metal coating layer is uniformly coated on the surface and pores of the porous carbon.

7. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, It meets one or more of the following conditions: (1) In step S2, the silane deposition is carried out in an inert gas atmosphere, preferably nitrogen; when the inert gas is nitrogen, the flow rate of the nitrogen is preferably 20-60 L / min, for example 40 L / min; (2) In step S2, the heat treatment temperature for silane deposition is 450-600℃, preferably 500-550℃; (3) In step S2, the flow rate of the silane is 5-20 L / min, for example 10 L / min; (4) In step S2, the heat treatment time for the silane deposition is 2-10 h, preferably 5-8 h, for example 6.5 h; (5) In step S2, the silane deposition is performed using chemical vapor deposition. (6) In step S2, the silane deposition is carried out in a fluidized bed reactor; (7) In step S3, the carbon source gas includes one or more of acetylene, methane, propane and octane, for example, acetylene or a mixture of methane and acetylene; (8) In step S3, the heat treatment temperature is 500-1000℃, preferably 600-900℃, more preferably 650-750℃, for example 500℃, 700℃ or 1000℃; (9) In step S3, the heat treatment time is 2-10h, preferably 3-8h, more preferably 3-5h, for example 2h, 4h or 10h.

8. A silicon-carbon anode material, which is prepared according to the method for preparing silicon-carbon anode materials as described in any one of claims 1-7.

9. A silicon-carbon anode material, characterized in that, It includes a porous carbon matrix, a metal coating layer, an amorphous silicon layer, and a carbon coating layer; the metal coating layer is located on the surface of the porous carbon matrix, the amorphous silicon layer is located on the surface of the metal coating layer, and the carbon coating layer is located on the surface of the amorphous silicon layer; the thickness of the metal coating layer is 0.5-50 nm, preferably 0.5-15 nm, for example 0.5 nm, 5 nm, or 15 nm; The metal elements in the metal cladding layer preferably include one or more of Al, Ti, Ge, and Cu; The metal cladding layer is preferably a single metal layer and / or a metal oxide layer; The metal cladding layer preferably uniformly coats the surface and pores of the porous carbon.

10. A lithium-ion battery, characterized in that, It includes the silicon-carbon anode material as described in claim 8 or 9.

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