Preparation method of silicon-carbon negative electrode material, silicon-carbon negative electrode material and application thereof

Abstract

The application relates to a preparation method of a silicon-carbon negative electrode material, the silicon-carbon negative electrode material and an application preparation method thereof. The preparation method comprises the following steps: depositing nitrogen elements in the pores and on the surface of a porous carbon base body, so that part of the nitrogen elements form C-N bonds with carbon elements; then depositing nano-silicon particles in the pores of the nitrogen-doped porous carbon base body, the C-N bonds can induce the formation of Si-N bonds in the material; then carbon deposition is carried out; then the processes of silicon deposition and carbon deposition are alternately carried out, a carbon interlayer structure is formed on the pores and the surface of the porous carbon base body, the nano-silicon particles are isolated, carbon coating treatment is carried out, and the silicon-carbon negative electrode material is obtained; the silicon-carbon negative electrode material is used as a negative electrode active material to prepare a negative electrode sheet, and the negative electrode sheet is applied in a lithium ion battery, so that the conductivity and the cycle stability of the lithium ion battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a method for preparing a silicon-carbon anode material, the silicon-carbon anode material itself, and its applications. Background Technology

[0002] With the accelerating pace of product updates in consumer electronics and new energy vehicles, new demands are being placed on high-efficiency energy storage devices. Lithium-ion batteries are one of the main energy storage devices. Currently, traditional graphite anode materials, due to their relatively low theoretical capacity limit (372 mAh / g), can no longer meet the development needs. Silicon materials, with their high theoretical specific capacity of 4200 mAh / g, low lithium intercalation potential, and low cost, are expected to become the next generation of lithium-ion battery anode materials. However, silicon as an anode material undergoes a volume expansion of more than 300% during lithium intercalation and deintercalation, leading to material pulverization and the formation of an unstable solid electrolyte layer (SEI) on the material surface, resulting in irreversible capacity decay. Simultaneously, silicon's poor conductivity prevents effective capacity release under high-rate conditions. These problems severely limit the application of silicon anode materials in lithium-ion batteries.

[0003] Currently, the main methods for reducing the expansion of silicon anode materials are silicon particle nanosizing and carbon layer coating. However, due to the poor conductivity of silicon itself and the significant volume changes of the carbon coating on the silicon-based material, the coating structure is difficult to maintain long-term stability. Therefore, there is an urgent need to develop a novel silicon-carbon composite material to solve these problems. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing silicon-carbon anode materials, silicon-carbon anode materials, and their applications.

[0005] To achieve the above objectives, in a first aspect, embodiments of the present invention provide a method for preparing a silicon-carbon anode material, the method comprising:

[0006] Step S1: Place the porous carbon matrix in a vapor deposition furnace, introduce a first mixed gas of protective gas and nitrogen source gas, heat to a first temperature and then perform a first heat preservation, so that the nitrogen element obtained by decomposing the nitrogen source gas is deposited in the pores and surface of the porous carbon matrix, and after cooling to room temperature, a nitrogen-doped porous carbon matrix is ​​obtained.

[0007] Step S2: In a protective gas environment, the vapor deposition furnace is heated to a second temperature, and then a second mixed gas of protective gas and silicon source gas is introduced for a second heat preservation, so that the silicon element obtained by decomposing the silicon source gas is deposited into the pores and surface of the nitrogen-doped porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, an intermediate material is obtained.

[0008] Step S3: In a protective gas environment, the vapor deposition furnace is heated to a third temperature, and then a third mixed gas of protective gas and carbon source gas is introduced for a third heat preservation, so that the carbon elements obtained by decomposing the carbon source gas are deposited in the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0009] Step S4: Repeat steps S2 and S3 alternately on the precursor material to obtain a silicon-carbon composite material.

[0010] Step S5: The silicon-carbon composite material is subjected to carbon coating treatment to finally obtain the silicon-carbon anode material.

[0011] Preferably, in step S1, the particle size D50 of the porous carbon matrix is ​​4 μm to 20 μm;

[0012] The porous carbon matrix has a pore size of 0–4 nm, but not including 0;

[0013] The porous carbon matrix has a micropore content of 10% to 100%.

[0014] The nitrogen source gas includes one or more of ammonia, nitric oxide, and nitrogen dioxide.

[0015] The protective gas includes nitrogen and / or argon;

[0016] In the first mixed gas, the flow ratio of the nitrogen source gas to the protective gas is 1:15 to 5:6;

[0017] The first temperature is 400℃~1200℃, and the first heat preservation time is 10min~160min;

[0018] In the nitrogen-doped porous carbon matrix, nitrogen forms CN bonds with carbon.

[0019] Preferably, in step S2, the silicon source gas includes one or more gases selected from silane, disilane, trichlorosilane, and tetrachlorosilane.

[0020] The protective gas includes nitrogen and / or argon;

[0021] In the second mixed gas, the flow rate ratio of the silicon source gas to the protective gas is 1:15 to 23:30;

[0022] The second temperature is 400℃~800℃, and the second heat preservation time is 10min~160min;

[0023] The silicon in the intermediate material forms Si-N bonds with nitrogen.

[0024] Preferably, in step S3, the carbon source gas includes one or more of acetylene, methane, and propylene;

[0025] In the third mixed gas, the flow ratio of the carbon source gas to the protective gas is 1:15 to 1:1;

[0026] The third temperature is 500℃~800℃, and the third heat preservation time is 10min~120min;

[0027] The preparation process of alternatingly repeating steps S2 and S3 is performed 1 to 5 times.

[0028] Preferably, in step S4, the preparation process of alternatingly repeating step S2 and step S3 is performed 2 to 5 times.

[0029] Preferably, in step S5, the carbon coating process is gas-phase coating;

[0030] The carbon source gas used for the gas phase coating includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide.

[0031] The temperature of the gas phase coating is 400℃~800℃, and the holding time is 2 hours~10 hours.

[0032] In a second aspect, embodiments of the present invention provide a silicon-carbon anode material prepared based on the preparation method described in the first aspect, the silicon-carbon anode material comprising: a silicon-carbon composite material and a carbon coating layer covering the silicon-carbon composite material;

[0033] The silicon-carbon composite material includes: a porous carbon matrix, and composite particles attached to the pores of the porous carbon matrix;

[0034] The composite particles include: nano-silicon particles and nitrogen-doped silicon particles, and a composite layer coating the surfaces of the nano-silicon particles and nitrogen-doped silicon particles;

[0035] The composite layer includes one or more carbon layers and one or more silicon layers; the layer of the composite layer closest to the outer surface of the nano-silicon particles and nitrogen-doped silicon particles is a carbon layer, and the outermost layer is also a carbon layer.

[0036] Preferably, the silicon-carbon anode material has a particle size D50 between 3 μm and 15 μm and a specific surface area of ​​1800 m². 2 / g~2400m 2 / g;

[0037] The proportion of nano-silicon particles in the silicon-carbon anode material is 40wt% to 50wt%.

[0038] The nitrogen content in the silicon-carbon anode material is 0.1 wt% to 2 wt%.

[0039] Thirdly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising the silicon-carbon negative electrode material described in the second aspect above.

[0040] Fourthly, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the third aspect above.

[0041] The present invention provides a method for preparing a silicon-carbon anode material, the silicon-carbon anode material itself, and its applications, which have the following beneficial effects:

[0042] (1) The method for preparing a silicon-carbon anode material provided in the embodiments of the present invention firstly deposits nitrogen element in the pores and surface of a porous carbon matrix, so that some nitrogen element forms CN bond with carbon element; then deposits nano-silicon particles in the pores of the nitrogen-doped porous carbon matrix, and CN bond can induce the formation of Si-N bond inside the material; then carbon deposition is performed; then silicon deposition and carbon deposition processes are alternated to form a carbon interlayer structure such as carbon-silicon-carbon-silicon-carbon in the pores and surface of the porous carbon matrix, which isolates the nano-silicon particles; finally, carbon coating treatment is performed to obtain silicon-carbon anode material.

[0043] (2) The silicon-carbon anode material prepared by the above preparation method in the embodiments of the present invention can induce the formation of Si-N bonds inside the material by the CN bond formed by the nitrogen doping part of the nitrogen, thereby improving the uniformity of silicon deposition. The excess nitrogen element improves the conductivity of silicon-carbon material without affecting other electrochemical properties of the material. The carbon interlayer structure of the material can provide a buffer for the expansion of nano-silicon particles and enhance the stability of the material.

[0044] (3) Using the silicon-carbon anode material provided in the embodiments of the present invention as the anode active material to prepare anode sheet, and applying the anode sheet in lithium-ion batteries can improve the conductivity and cycle stability of lithium-ion batteries. Attached Figure Description

[0045] Figure 1 A flowchart illustrating the preparation method of silicon-carbon anode material provided in an embodiment of the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0048] This invention provides a method for preparing a silicon-carbon anode material, such as... Figure 1 As shown, the specific steps include:

[0049] Step S1: Place the porous carbon matrix in a vapor deposition furnace, introduce a first mixed gas of protective gas and nitrogen source gas, heat to a first temperature and then hold for a first time, so that the nitrogen element obtained by decomposing the nitrogen source gas is deposited in the pores and on the surface of the porous carbon matrix. After cooling to room temperature, a nitrogen-doped porous carbon matrix is ​​obtained.

[0050] In this process, after the porous carbon matrix is ​​placed in the vapor deposition furnace, a protective gas is first introduced to purge the air from the vapor deposition furnace, and then a first mixed gas of protective gas and nitrogen source gas is introduced.

[0051] In nitrogen-doped porous carbon matrices, nitrogen forms CN bonds with carbon.

[0052] The particle size D50 of the porous carbon matrix is ​​4 μm to 20 μm;

[0053] The pore size of the porous carbon matrix is ​​greater than 0 and less than or equal to 4 nm.

[0054] The proportion of micropores in the total pores of the porous carbon matrix is ​​10% to 100%, preferably 70% to 100%;

[0055] Nitrogen source gases include one or more of ammonia, nitric oxide, and nitrogen dioxide.

[0056] Protective gases include nitrogen and / or argon;

[0057] In the first mixed gas, the flow ratio of nitrogen source gas to protective gas is 1:15 to 5:6;

[0058] The first temperature is 400℃~1200℃, and the first holding time is 10min~160min.

[0059] Step S2: In a protective gas environment, the vapor deposition furnace is heated to a second temperature, and then a second mixed gas of protective gas and silicon source gas is introduced for a second heat preservation, so that the silicon element obtained by decomposing the silicon source gas is deposited into the pores and surface of the nitrogen-doped porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, an intermediate material is obtained.

[0060] In this intermediate material, silicon forms Si-N bonds with nitrogen;

[0061] The silicon source gas includes one or more of the following: silane, silane, trichlorosilane, and tetrachlorosilane;

[0062] Protective gases include nitrogen and / or argon;

[0063] In the second mixed gas, the flow ratio of silicon source gas to protective gas is 1:15 to 23:30;

[0064] The second temperature is 400℃~800℃, and the second holding time is 10min~160min.

[0065] Step S3: In a protective gas environment, the vapor deposition furnace is heated to a third temperature, and then a third mixed gas of protective gas and carbon source gas is introduced for a third heat preservation, so that the carbon elements obtained by decomposing the carbon source gas are deposited in the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0066] The carbon source gases include one or more of acetylene, methane, and propylene.

[0067] In the third mixed gas, the flow ratio of carbon source gas to protective gas is 1:15 to 1:1; wherein the protective gas includes nitrogen or argon, preferably nitrogen;

[0068] In addition, in an optional scheme, ammonia gas may be included in the third mixed gas in addition to the carbon source gas and the protective gas, so as to form NC bonds in the sandwich structure, thereby improving the conductivity of the material.

[0069] The third temperature is 500℃~800℃, and the third holding time is 10min~120min.

[0070] Step S4: For the precursor material, the preparation process of steps S2 and S3 is repeated alternately to obtain the silicon-carbon composite material.

[0071] The preparation process of alternating steps S2 and S3 is repeated 1 to 5 times, preferably 2 to 5 times.

[0072] Step S5: The silicon-carbon composite material is subjected to carbon coating treatment to finally obtain the silicon-carbon anode material;

[0073] Among them, the carbon coating treatment is gas phase coating;

[0074] The carbon source gas used for gas phase coating includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide;

[0075] The temperature for vapor phase coating is 400℃~800℃, and the holding time is 2 hours~10 hours.

[0076] In this invention, nitrogen doping can alter the electronic structure and surface chemical properties of the porous carbon matrix, thereby constructing new pseudocapacitive active sites and improving the conductivity of the porous carbon matrix as a carbon framework. After nitrogen atom doping of the porous carbon matrix, the resulting sites change the electron cloud structure on the material surface, thereby inducing the deposition of silicon.

[0077] The silicon-carbon anode material prepared by the above-described preparation method in this embodiment of the invention comprises: a silicon-carbon composite material and a carbon coating layer covering the silicon-carbon composite material; the particle size D50 of the silicon-carbon anode material is between 3 μm and 15 μm, and the specific surface area is 1800 m². 2 / g~2400m 2 / g.

[0078] The silicon-carbon composite material includes a porous carbon matrix and composite particles attached to the pores of the porous carbon matrix.

[0079] The composite particles include: nano-silicon particles and nitrogen-doped silicon particles, as well as a composite layer coating the surfaces of the nano-silicon particles and nitrogen-doped silicon particles.

[0080] The composite layer includes one or more carbon layers and one or more silicon layers; the layer closest to the outer surface of the nano-silicon particles and nitrogen-doped silicon particles is a carbon layer, and the outermost layer is also a carbon layer.

[0081] The proportion of nano-silicon particles in the silicon-carbon anode material is 40wt% to 50wt%; the proportion of nitrogen in the silicon-carbon anode material is 0.1wt% to 2wt%.

[0082] The silicon-carbon anode material provided in this embodiment of the invention can be used as an anode active material to prepare anode sheets, which can be applied in lithium-ion batteries.

[0083] Because of the silicon-carbon anode material provided in this embodiment of the invention, the CN bond formed by nitrogen doping can induce the formation of Si-N bonds inside the material, thereby improving the uniformity of silicon deposition. The excess nitrogen element improves the conductivity of the silicon-carbon material without affecting other electrochemical properties. The carbon interlayer structure of the material can provide a buffer for the expansion of nano-silicon particles, and the enhanced stability of the material can improve the conductivity and cycle stability of lithium-ion batteries.

[0084] To better understand the technical solution provided by the present invention, the preparation process and characteristics of the silicon-carbon anode material of the present invention are illustrated below with several specific examples.

[0085] Example 1

[0086] This embodiment provides a process for preparing a silicon-carbon anode material, the specific process of which is as follows.

[0087] (1) Place 5 kg of porous carbon matrix in a vapor deposition furnace, introduce nitrogen gas to remove the air in the vapor deposition furnace, heat the vapor deposition furnace to 550°C, and then introduce a mixture of nitrogen and ammonia gas with a flow ratio of 20:30. Continue to circulate the gas and keep it at the temperature for 40 min, so that the nitrogen element obtained by the decomposition of ammonia gas is deposited in the pores and on the surface of the porous carbon matrix. After cooling to room temperature, a nitrogen-doped porous carbon matrix containing CN bonds is obtained.

[0088] (2) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and silane is introduced, wherein the flow ratio of silane to nitrogen is 16:30. The furnace is kept at this temperature for 60 min, so that the silicon element obtained by the decomposition of silane is deposited into the pores and surface of the nitrogen-doped porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, an intermediate material containing Si-N bonds is obtained.

[0089] (3) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and acetylene is introduced, with a flow ratio of acetylene to nitrogen of 5:18. The mixture is kept at this temperature for 10 minutes, so that the carbon elements obtained from the decomposition of the carbon source gas are deposited into the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0090] (4) Repeat steps (2) and (3) three times alternately to prepare the precursor material to obtain the silicon-carbon composite material.

[0091] (5) The silicon-carbon composite material is vapor-phase coated to obtain silicon-carbon anode material. The specific process is as follows: Under nitrogen atmosphere, the vapor deposition furnace is heated to 550℃ at a heating rate of 5℃ / min. A mixed gas of acetylene and nitrogen is introduced at a volume ratio of 16:30. The silicon-carbon composite material is vapor-phase coated and kept at the temperature for 4 hours. Then the gas source is turned off. A carbon coating layer is formed on the outermost surface of the silicon-carbon composite material. After cooling to room temperature, the material is discharged and finally silicon-carbon anode material is obtained.

[0092] The silicon-carbon anode material prepared in this embodiment was used as the anode active material to prepare the anode sheet, and then assembled into a coin cell for testing. The specific process is as follows.

[0093] Preparation of negative electrode sheet: The silicon-carbon negative electrode material prepared in this embodiment, acetylene black and carboxymethyl cellulose (CMC) are placed in a mortar in a mass ratio of 9:0.5:0.5, ground thoroughly, and then an appropriate amount of deionized water is added. The mixture is then pulped in a pulping machine to form a slurry. The slurry is coated onto a copper foil current collector and dried in a vacuum oven at 85°C for 10 hours. The dried electrode sheet is then cut into round pieces with a diameter of 14 mm as negative electrode sheets. Multiple negative electrode sheets can be cut and placed in a glove box for later use.

[0094] Assemble coin cell: Assemble at least two coin cells in an argon-filled glove box using conventional methods. The electrolyte is lithium hexafluorophosphate (LiPF6) with a molar concentration of 1 mol / L. The solvent of the electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DMC, and DEC of 1:1:1. A polyethylene diaphragm is used as the separator, and a lithium sheet is used as the counter electrode.

[0095] Cyclic testing process: The electrochemical performance of the battery was evaluated using the Blue Battery testing system. Test conditions: Voltage window: 0.01V to 2V; Discharge rate: 0.1C; Lower limit of discharge voltage window: 0.01V; Capacity retention after 200 test cycles.

[0096] Expansion rate test of the electrode sheet after the first charge-discharge cycle: At room temperature, the prepared negative electrode sheet was cut by ion beam, and the cross-section was photographed using a scanning electron microscope. The thickness of the negative electrode sheet was measured and recorded as T1, and the thickness of the copper foil current collector substrate was measured and recorded as T2. Under a current density of 0.1C and a charging cutoff voltage of 2V, the coin cell was fully charged. Then, the battery was disassembled in a glove box, the negative electrode sheet was removed, and after ion beam cutting, the cross-section was photographed again using SEM, and the thickness of the negative electrode sheet at this time was measured and recorded as T3. Then, the initial expansion rate was calculated using the following formula:

[0097] First-cycle expansion rate = (T3-T1) / (T1-T2)×100%.

[0098] Conductivity test: Weigh 0.5g of the silicon-carbon anode material prepared in this embodiment and place it in a powder resistivity tester. Set the pressure to 20MPa and perform a powder conductivity test. Calculate the conductivity.

[0099] The capacity retention rate, electrode expansion rate in the first cycle, and material conductivity data of the coin cell tested in this embodiment after 200 cycles are detailed in Table 1.

[0100] Example 2

[0101] This embodiment provides a preparation process for silicon-carbon anode material, which differs from Embodiment 1 in the temperature of step (1): 5 kg of porous carbon matrix is ​​placed in a vapor deposition furnace, nitrogen gas is introduced to remove the air in the vapor deposition furnace, the vapor deposition furnace is heated to 600°C, and then a mixture of nitrogen and ammonia gas is introduced, wherein the flow ratio of ammonia to nitrogen is 20:30, and the gas is continuously introduced and kept at the temperature for 40 min, so that the nitrogen element obtained by the decomposition of ammonia gas is deposited in the pores and surface of the porous carbon matrix. After cooling to room temperature, a nitrogen-doped porous carbon matrix containing CN bonds is obtained.

[0102] The other preparation steps are the same as in Example 1.

[0103] The silicon-carbon anode material prepared in this embodiment was used as the anode active material to prepare anode sheets, which were then assembled into coin cells for testing. The specific preparation of the anode sheets, the assembly process of the coin cells, and the testing process were all the same as in Example 1.

[0104] The capacity retention rate, electrode expansion rate in the first cycle, and material conductivity data of the coin cell tested in this embodiment after 200 cycles are detailed in Table 1.

[0105] Example 3

[0106] This embodiment provides a preparation process for silicon-carbon anode material, which differs from Embodiment 1 in step (4): the preparation process of steps (2) and (3) is repeated 5 times alternately on the precursor material to obtain silicon-carbon composite material.

[0107] The other preparation steps are the same as in Example 1.

[0108] The silicon-carbon anode material prepared in this embodiment was used as the anode active material to prepare anode sheets, which were then assembled into coin cells for testing. The specific preparation of the anode sheets, the assembly process of the coin cells, and the testing process were all the same as in Example 1.

[0109] The capacity retention rate, electrode expansion rate in the first cycle, and material conductivity data of the coin cell tested in this embodiment after 200 cycles are detailed in Table 1.

[0110] Example 4

[0111] This embodiment provides a preparation process for silicon-carbon anode material. The difference from Embodiment 1 is that in step (2), the flow ratio of silane to nitrogen is 20:30. The other preparation processes in step (4) are the same as in Embodiment 1.

[0112] The other preparation steps are the same as in Example 1.

[0113] The silicon-carbon anode material prepared in this embodiment was used as the anode active material to prepare anode sheets, which were then assembled into coin cells for testing. The specific preparation of the anode sheets, the assembly process of the coin cells, and the testing process were all the same as in Example 1.

[0114] The capacity retention rate, electrode expansion rate in the first cycle, and material conductivity data of the coin cell tested in this embodiment after 200 cycles are detailed in Table 1.

[0115] Example 5

[0116] This embodiment provides a preparation process for silicon-carbon anode material. The difference from embodiment 1 is that in step (3): under nitrogen gas environment, the vapor deposition furnace is heated to 550°C, and then a mixed gas of acetylene, ammonia and nitrogen with a flow ratio of 18:3:5 is introduced and kept at the temperature for 10 minutes, so that the carbon elements obtained by the decomposition of carbon source gas are deposited in the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0117] The other preparation steps are the same as in Example 1.

[0118] The silicon-carbon anode material prepared in this embodiment was used as the anode active material to prepare anode sheets, which were then assembled into coin cells for testing. The specific preparation of the anode sheets, the assembly process of the coin cells, and the testing process were all the same as in Example 1.

[0119] The capacity retention rate, electrode expansion rate in the first cycle, and material conductivity data of the coin cell tested in this embodiment after 200 cycles are detailed in Table 1.

[0120] To better illustrate the effects of the embodiments of the present invention, comparative examples 1-3 are compared with the above embodiments.

[0121] Comparative Example 1

[0122] This comparative example provides a method for preparing a negative electrode material. Unlike Example 1, it does not perform the nitrogen doping process of step (1) in Example 1, so nitrogen is not pre-deposited and CN bonds are not pre-formed. Si-N bonds are also not formed during silicon deposition. The specific preparation process of this comparative example is as follows.

[0123] (1) In a nitrogen atmosphere, 5 kg of porous carbon matrix was placed in a vapor deposition furnace and heated to 550 °C. Then, a mixture of nitrogen and silane was introduced, with a flow ratio of silane to nitrogen of 16:30. The mixture was kept at the temperature for 40 min, so that the silicon element obtained by the decomposition of silane was deposited into the pores and surface of the porous carbon matrix and grown into nano-silicon particles. After cooling to room temperature, an intermediate material was obtained.

[0124] (2) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and acetylene is introduced, with a flow ratio of acetylene to nitrogen of 18:5. The mixture is kept at this temperature for 10 minutes, so that the carbon elements obtained from the decomposition of the carbon source gas are deposited into the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0125] (3) Repeat steps (1) and (2) three times alternately to prepare the precursor material to obtain silicon-carbon composite material.

[0126] (4) The silicon-carbon composite material is vapor-phase coated to obtain the negative electrode material. The specific process is as follows: Under nitrogen atmosphere, the vapor deposition furnace is heated to 550°C at a heating rate of 5°C / min. A mixture of acetylene and nitrogen gas is introduced at a volume ratio of 16:30. The silicon-carbon composite material is vapor-phase coated and kept at the temperature for 4 hours. The gas source is then turned off, and a carbon coating layer is formed on the outermost surface of the silicon-carbon composite material. After cooling to room temperature, the material is discharged to obtain the negative electrode material.

[0127] The negative electrode material prepared in this comparative example was used to prepare a negative electrode sheet, which was then assembled into a coin cell for testing. The specific preparation of the negative electrode sheet, the assembly process of the coin cell, and the testing process were all the same as in Example 1.

[0128] Table 1 details the capacity retention, electrode expansion rate, and material conductivity data of the coin cells in this comparative test after 200 cycles.

[0129] Comparative Example 2

[0130] This comparative example provides a process for preparing a negative electrode material. Unlike Example 1, it does not perform the alternating deposition process of step (4) in Example 1. The specific process is as follows.

[0131] (1) Place 5 kg of porous carbon matrix in a vapor deposition furnace, introduce nitrogen gas to remove the air in the vapor deposition furnace, heat the vapor deposition furnace to 550°C, and then introduce a mixture of nitrogen and ammonia gas with a flow ratio of 20:30. Continue to circulate the gas and keep it at the temperature for 40 min, so that the nitrogen element obtained by the decomposition of ammonia gas is deposited in the pores and on the surface of the porous carbon matrix. After cooling to room temperature, a nitrogen-doped porous carbon matrix containing CN bonds is obtained.

[0132] (2) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and silane is introduced, wherein the flow ratio of silane to nitrogen is 16:30. The temperature is maintained for 120 min, so that the silicon element obtained by the decomposition of silane is deposited into the pores and surface of the nitrogen-doped porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, an intermediate material containing Si-N bonds is obtained.

[0133] (3) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and acetylene is introduced, with a flow ratio of acetylene to nitrogen of 18:5. The mixture is kept at this temperature for 10 minutes, so that the carbon elements obtained from the decomposition of the carbon source gas are deposited into the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained.

[0134] (4) The precursor material is vapor-phase coated to obtain the anode material. The specific process is as follows: Under nitrogen atmosphere, the vapor deposition furnace is heated to 550°C at a heating rate of 5°C / min. A mixture of acetylene and nitrogen gas is introduced at a volume ratio of 16:30. The silicon-carbon composite material is vapor-phase coated and kept at the temperature for 4 hours. The gas source is then turned off, and a carbon coating layer is formed on the outermost surface of the silicon-carbon composite material. After cooling to room temperature, the material is discharged, and the anode material is finally obtained.

[0135] The negative electrode material prepared in this comparative example was used to prepare a negative electrode sheet, which was then assembled into a coin cell for testing. The specific preparation of the negative electrode sheet, the assembly process of the coin cell, and the testing process were all the same as in Example 1.

[0136] Table 1 details the capacity retention, electrode expansion rate, and material conductivity data of the coin cells in this comparative test after 200 cycles.

[0137] Comparative Example 3

[0138] This comparative example provides a preparation process for a traditional silicon-carbon anode material, the specific process of which is as follows.

[0139] (1) In a nitrogen atmosphere, the vapor deposition furnace is heated to 550°C, and then a mixture of nitrogen and silane is introduced, wherein the flow ratio of silane to nitrogen is 16:30. The furnace is kept at this temperature for 120 min, so that the silicon element obtained by the decomposition of silane is deposited into the pores and surface of the porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, the precursor material is obtained.

[0140] (2) The precursor material is vapor-phase coated to obtain the traditional silicon-carbon anode material. The specific process is as follows: Under nitrogen atmosphere, the vapor deposition furnace is heated to 550°C at a heating rate of 5°C / min. A mixture of acetylene and nitrogen gas is introduced at a volume ratio of 16:30. The silicon-carbon composite material is vapor-phase coated and kept at the temperature for 4 hours. The gas source is then turned off, and a carbon coating layer is formed on the outermost surface of the silicon-carbon composite material. After cooling to room temperature, the material is discharged, and the final traditional silicon-carbon anode material is obtained.

[0141] The conventional silicon-carbon anode material prepared in this comparative example was used to prepare a negative electrode sheet, which was then assembled into a coin cell for testing. The specific preparation of the negative electrode sheet, the assembly process of the coin cell, and the testing process were all the same as in Example 1.

[0142] Table 1 details the capacity retention, electrode expansion rate, and material conductivity data of the coin cells in this comparative test after 200 cycles.

[0143] Table 1 summarizes the test data for Examples 1-5 and Comparative Examples 1-3:

[0144]

[0145]

[0146] Table 1

[0147] The comparison of test data in Table 1 shows that: the conductivity of the silicon-carbon anode materials prepared in Examples 1-5 is much higher than that in Comparative Examples 1-3; the expansion rate of the electrodes in Examples 1-5 after the first charge-discharge cycle is lower than that in Comparative Examples 1-3; and the cycle capacity retention rate of the coin half-cells assembled in Examples 1-5 after 200 cycles is much higher than that in Comparative Examples 1-3. This is because, in the preparation of silicon-carbon anode materials, Examples 1-5 first modified the porous carbon matrix with nitrogen to generate CN sites that can induce silicon deposition, improving the uniformity of the silicon deposition process and increasing the overall conductivity of the material. Through the alternating deposition of silicon and carbon, a sandwich structure carbon layer is formed. This sandwich structure can effectively buffer the pressure generated by the expansion of internal nano-silicon particles, effectively solving the problem of silicon expansion during battery cycling and improving the battery's conductivity.

[0148] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, The preparation method includes: Step S1: Place the porous carbon matrix in a vapor deposition furnace, introduce a first mixed gas of protective gas and nitrogen source gas, heat to a first temperature and then perform a first heat preservation, so that the nitrogen element obtained by decomposing the nitrogen source gas is deposited in the pores and surface of the porous carbon matrix, and after cooling to room temperature, a nitrogen-doped porous carbon matrix is ​​obtained. Step S2: In a protective gas environment, the vapor deposition furnace is heated to a second temperature, and then a second mixed gas of protective gas and silicon source gas is introduced for a second heat preservation, so that the silicon element obtained by decomposing the silicon source gas is deposited into the pores and surface of the nitrogen-doped porous carbon matrix and grows into nano-silicon particles. After cooling to room temperature, an intermediate material is obtained. Step S3: In a protective gas environment, the vapor deposition furnace is heated to a third temperature, and then a third mixed gas of protective gas and carbon source gas is introduced for a third heat preservation, so that the carbon elements obtained by decomposing the carbon source gas are deposited in the pores and surface of the intermediate material. After cooling to room temperature, the precursor material is obtained. Step S4: Repeat steps S2 and S3 alternately on the precursor material to obtain a silicon-carbon composite material. Step S5: The silicon-carbon composite material is subjected to carbon coating treatment to finally obtain the silicon-carbon anode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the particle size D50 of the porous carbon matrix is ​​4 μm to 20 μm; The porous carbon matrix has a pore size of 0–4 nm, but not including 0; The porous carbon matrix has a micropore content of 10% to 100%. The nitrogen source gas includes one or more of ammonia, nitric oxide, and nitrogen dioxide. The protective gas includes nitrogen and / or argon; In the first mixed gas, the flow ratio of the nitrogen source gas to the protective gas is 1:15 to 5:6; The first temperature is 400℃~1200℃, and the first heat preservation time is 10min~160min; In the nitrogen-doped porous carbon matrix, nitrogen forms CN bonds with carbon.

3. The preparation method according to claim 1, characterized in that, In step S2, the silicon source gas includes one or more gases selected from silane, silane, trichlorosilane, and tetrachlorosilane. The protective gas includes nitrogen and / or argon; In the second mixed gas, the flow rate ratio of the silicon source gas to the protective gas is 1:15 to 23:30; The second temperature is 400℃~800℃, and the second heat preservation time is 10min~160min; The silicon in the intermediate material forms Si-N bonds with nitrogen.

4. The preparation method according to claim 1, characterized in that, In step S3, the carbon source gas includes one or more of acetylene, methane, and propylene. In the third mixed gas, the flow ratio of the carbon source gas to the protective gas is 1:15 to 1:1; The third temperature is 500℃~800℃, and the third heat preservation time is 10min~120min; The preparation process of alternatingly repeating steps S2 and S3 is performed 1 to 5 times.

5. The preparation method according to claim 1, characterized in that, In step S4, the preparation process of alternatingly repeating step S2 and step S3 is performed 2 to 5 times.

6. The preparation method according to claim 1, characterized in that, In step S5, the carbon coating process is a gas-phase coating. The carbon source gas used for the gas phase coating includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide. The temperature of the gas phase coating is 400℃~800℃, and the holding time is 2 hours~10 hours.

7. A silicon-carbon anode material prepared by any one of the preparation methods according to claims 1-6, characterized in that, The silicon-carbon anode material includes: a silicon-carbon composite material and a carbon coating layer covering the silicon-carbon composite material; The silicon-carbon composite material includes: a porous carbon matrix, and composite particles attached to the pores of the porous carbon matrix; The composite particles include: nano-silicon particles and nitrogen-doped silicon particles, and a composite layer coating the surfaces of the nano-silicon particles and nitrogen-doped silicon particles; The composite layer includes one or more carbon layers and one or more silicon layers; the layer of the composite layer closest to the outer surface of the nano-silicon particles and nitrogen-doped silicon particles is a carbon layer, and the outermost layer is also a carbon layer.

8. The silicon-carbon anode material according to claim 7, characterized in that, The silicon-carbon anode material has a particle size D50 between 3 μm and 15 μm and a specific surface area of ​​1800 m². 2 / g~2400m 2 / g; The proportion of nano-silicon particles in the silicon-carbon anode material is 40wt% to 50wt%. The nitrogen content in the silicon-carbon anode material is 0.1 wt% to 2 wt%.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the silicon-carbon negative electrode material as described in any one of claims 7-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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