Lithium battery silicon-carbon negative electrode material and preparation method and application thereof

Abstract

This invention relates to a silicon-carbon anode material for lithium batteries, its preparation method, and its application. The preparation method includes: Step 1, placing a porous carbon matrix in a vapor deposition furnace under a protective atmosphere; Step 2, introducing a first mixture of silicon source gas and protective gas to perform silicon deposition; Step 3, introducing a second mixture of carbon source gas and protective gas to perform interlayer deposition of carbon layers; Step 4, repeating Step 2 and Step 3 1-5 times to form a silicon-carbon composite material with a pre-coated interlayer structure; Step 5, performing carbon coating treatment on the silicon-carbon composite material with the pre-coated interlayer structure to obtain a silicon-carbon composite material with a carbon coating layer; Step 6, mixing the silicon-carbon composite material with the carbon coating layer uniformly in a solution containing a silane coupling agent, spray drying the mixture, and then heat-treating the spray-dried material to obtain the silicon-carbon anode material for lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode material technology, and in particular to a silicon-carbon anode material for lithium batteries, its preparation method, and its application. 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 volume expansion (>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, silicon itself has poor conductivity, so adding a carbon coating layer is more commonly used to improve the conductivity and suppress volume expansion. However, silicon-based materials have a relatively large volume change rate, and the carbon coating layer structure is difficult to maintain long-term stability under the huge volume changes of silicon-based materials. Therefore, under the current technological conditions, silicon-based materials still cannot well meet application requirements. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-carbon anode material for lithium batteries, its preparation method, and its applications. This technical solution solves the problems of volume expansion and insufficient conductivity in silicon-carbon anodes from both material structure and interface control perspectives by constructing a carbon sandwich structure and a silicon-oxygen coating layer.

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

[0006] Step 1: Under a protective atmosphere, place the porous carbon matrix into a vapor deposition furnace;

[0007] Step 2: Introduce the first mixture of silicon source gas and protective gas to perform silicon deposition;

[0008] Step 3: Introduce a second mixture of carbon source gas and protective gas to perform interlayer deposition of carbon layer;

[0009] Step 4: Repeat steps 2 and 3 1-5 times to form a silicon-carbon composite material with a sandwich structure pre-coated.

[0010] Step 5: Perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating to obtain a silicon-carbon composite material with carbon coating layer.

[0011] Step 6: The silicon-carbon composite material with carbon coating is mixed evenly in a solution containing silane coupling agent and then spray-dried. The spray-dried material is then heat-treated to obtain the lithium battery silicon-carbon anode material.

[0012] Preferably, the protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0013] Preferably, the porous carbon matrix has a particle size D50 of 4-20 μm and a pore size of less than or equal to 4 nm; the porous carbon matrix has a micropore ratio of 10%-100%.

[0014] Preferably, in the first mixed gas, the volume ratio of the silicon source gas to the protective gas is [2-23]:30;

[0015] The silicon source gas includes one or more of the following: silane, disilane, trichlorosilane, and silicon tetrachloride;

[0016] The protective gas includes: nitrogen and / or argon;

[0017] The silicon deposition temperature is 400-800℃ and the time is 10-160 min.

[0018] Preferably, in the second mixture, the volume ratio of the carbon source gas to the protective gas is [2-6]:18;

[0019] The carbon source gas includes one or more of acetylene, methane, and propylene.

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

[0021] The carbon layer is deposited at a temperature of 400-800℃ for 10-120 minutes.

[0022] Preferably, the silicon-carbon composite material with a sandwich structure pre-coated by carbon coating treatment is subjected to carbon coating treatment to obtain a silicon-carbon composite material with a carbon coating layer, specifically including:

[0023] The carbon source gas and protective gas are introduced at a volume ratio of [2-30]:30, and the carbon source gas and protective gas are kept at 400-800℃ for 2-10 hours to perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating.

[0024] The coated carbon source gas includes one or more of the following: acetylene, ethylene, propylene, methane, and carbon dioxide;

[0025] The protective gas includes nitrogen and / or argon.

[0026] Preferably, the mass ratio of the silicon-carbon composite material with carbon coating to the silane coupling group is 100:1-100:10;

[0027] The heat treatment is performed at a temperature of 500-600℃ for a time of 10-160 minutes.

[0028] Secondly, embodiments of the present invention provide a lithium battery silicon-carbon anode material prepared by the preparation method described in the first aspect.

[0029] Thirdly, embodiments of the present invention provide a lithium battery anode, comprising the lithium battery silicon-carbon anode material described in the second aspect above.

[0030] Thirdly, embodiments of the present invention provide a lithium battery, including the lithium battery negative electrode described in the third aspect above.

[0031] This invention provides a method for preparing a silicon-carbon anode material for lithium-ion batteries. The method involves alternating deposition of silicon and carbon on a porous carbon substrate using vapor deposition to form a sandwich structure, and then constructing a silicon-oxygen coating layer on the surface of the silicon-carbon composite material using a silane coupling agent. The carbon sandwich provides mechanical support to a certain extent, buffering the expansion force caused by volume changes in silicon during charging and discharging, thus extending the material's lifespan. The carbon layer acts as a conductive network, improving the electron transport efficiency between silicon particles and enhancing the overall conductivity of the anode. The carbon sandwich restricts the silicon deposition range, reducing particle size and ensuring uniform distribution, thereby improving electrochemical performance. The stability of the surface silicon-oxygen coating layer inhibits the growth of the solid electrolyte interphase (SEI) film, reducing irreversible capacity loss. The silicon-oxygen coating layer reduces direct contact between silicon particles and the electrolyte, minimizing side reactions. Furthermore, the polarity of the silicon-oxygen layer enhances the wettability of the electrolyte on the anode surface, improving the battery's electrochemical performance. The silicon-carbon anode material prepared by this invention exhibits advantages such as high first-cycle efficiency and long cycle life. Attached Figure Description

[0032] Figure 1 A flowchart illustrating the preparation method of silicon-carbon anode material for lithium batteries provided in this embodiment of the invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] This invention provides a method for preparing silicon-carbon anode materials for lithium batteries. Figure 1 The following is a flowchart of the preparation method provided in the embodiments of the present invention, in conjunction with... Figure 1 The technical solution of the present invention will be described below.

[0035] like Figure 1 As shown, the preparation method of the lithium battery silicon-carbon anode material of the present invention mainly includes the following steps.

[0036] Step 110: Under a protective atmosphere, place the porous carbon matrix into a vapor deposition furnace.

[0037] The protective atmosphere is either nitrogen or argon.

[0038] Porous carbon types in porous carbon matrix can include biomass-based, resin-based, coal-coke-based, and petroleum-based porous carbon materials.

[0039] The activation methods for porous carbon matrices can include physical activation or chemical activation. Physical activation (such as steam treatment at high temperatures) or chemical activation (such as alkali or acid immersion treatment) of porous carbon materials can adjust the pore structure, including specific surface area, total pore volume, and pore size distribution, thereby optimizing the distribution of silicon particles and the composite process. Therefore, in the actual implementation of the technical solution of this invention, before applying the porous carbon matrix, the activation process of the porous carbon matrix can be controlled to regulate the desired specific surface area and pore size distribution of the porous carbon, thereby increasing the contact area between silicon particles and porous carbon and enhancing the conductivity and stability of the composite material. Specific process control methods are well known to those skilled in the art and will not be elaborated here.

[0040] In this invention, a porous carbon matrix with a particle size D50 of 4-20 μm and a pore size of less than or equal to 4 nm is preferably used. The proportion of micropores (pore size 1-2 nm) is 10%-100%. By optimizing and limiting the proportion of micropores, the wettability of the electrolyte and the ion diffusion channels can be adjusted and optimized, thereby enhancing the kinetic performance of the material.

[0041] Step 120: Introduce the first mixture of silicon source gas and protective gas to perform silicon deposition;

[0042] In the first mixed gas, the volume ratio of silicon source gas to protective gas is [2-23]:30; the silicon source gas includes one or more of silane, silane, trichlorosilane, and silicon tetrachloride; the protective gas includes nitrogen and / or argon; the silicon deposition temperature is 400-800℃ and the time is 10-160min.

[0043] Step 130: A second mixture of carbon source gas and protective gas is introduced to perform interlayer deposition of carbon layer;

[0044] Specifically, in the second mixture, the volume ratio of carbon source gas to protective gas is [2-6]:18; the carbon source gas includes one or more of acetylene, methane, and propylene; the protective gas includes nitrogen and / or argon; the temperature for interlayer deposition of the carbon layer is 400-800℃ and the time is 10-120min.

[0045] Repeat steps 120 and 130 1-5 times to form a silicon-carbon composite material with a pre-coated sandwich structure. During the final repetition, step 130 may or may not be repeated. Figure 1 Only the case of completely repeating steps 120 and 130 is shown.

[0046] This invention utilizes the aforementioned vapor deposition method to alternately deposit silicon and carbon on a porous carbon substrate, forming a sandwich structure. This design mitigates the volume expansion of silicon, improves conductivity, and enables uniform distribution of silicon particles.

[0047] Because silicon has a high volume expansion rate during charging and discharging, the carbon interlayer can provide mechanical support to a certain extent and buffer the expansion force. At the same time, the carbon layer, as a conductive network, can improve the electron transport efficiency between silicon particles and enhance the overall conductivity of the negative electrode. In addition, the carbon interlayer restricts the silicon deposition range, which can reduce the particle size and achieve a more uniform distribution, thereby improving electrochemical performance.

[0048] Step 140: Perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating to obtain a silicon-carbon composite material with carbon coating layer.

[0049] The carbon source gas and protective gas are introduced at a volume ratio of [2-30]:30, and the mixture is kept at 400-800℃ for 2-10 hours to perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating.

[0050] The carbon source gas being coated includes one or more of acetylene, ethylene, propylene, methane, and carbon dioxide; the protective gas includes nitrogen and / or argon.

[0051] Step 150: The silicon-carbon composite material with carbon coating is mixed evenly in a solution containing silane coupling agent and then spray-dried. The material obtained by spray drying is then heat-treated to obtain the silicon-carbon anode material for lithium batteries.

[0052] During the mixing process, the silicon-carbon composite material with carbon coating and silane coupling groups are mixed without materials at a mass ratio of 100:1 to 100:10.

[0053] Spray drying can be a method of forming dried powder particles from a uniformly mixed liquid using a spray drying method. The above method is a commonly used technique in this field, and those skilled in the art can set specific process parameters according to actual needs; therefore, it will not be elaborated upon here.

[0054] The heat treatment temperature is 500-600℃ and the time is 10-160min.

[0055] Through this step 150, a silicon-oxygen coating layer can be constructed on the surface of a silicon-carbon composite material using a silane coupling agent. This surface modification can have multiple functions.

[0056] First, the silicon-oxygen coating reduces direct contact between silicon particles and the electrolyte, minimizing side reactions. Second, the stability of the surface silicon-oxygen coating inhibits the growth of the solid electrolyte interphase (SEI) film, reducing irreversible capacity loss. Furthermore, the polarity of the silicon-oxygen layer enhances the wettability of the electrolyte to the negative electrode surface, improving the battery's electrochemical performance.

[0057] The silicon-carbon anode material for lithium batteries prepared by the above-described preparation method of the present invention can be used in the anode of lithium batteries.

[0058] 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.

[0059] Example 1

[0060] This embodiment is used to prepare silicon-carbon anode materials for lithium batteries.

[0061] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0062] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into the vapor deposition furnace and the gas is continuously introduced for 10 minutes to perform silicon deposition.

[0063] S3, at 550℃, a mixture of acetylene and nitrogen in a volume ratio of 5:18 is introduced into the deposition furnace and the gas is continuously introduced for 10 minutes to carry out interlayer deposition of carbon layers.

[0064] Repeat steps S2 and S3 three times to obtain a silicon-carbon composite material with a sandwich structure pre-coated.

[0065] S4. The obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixed gas of acetylene and nitrogen in a ratio of 16:30. The coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained.

[0066] S5. The silicon-carbon composite material and tetraethyl silicate are mixed at a mass ratio of 100:3, and the mixture is spray-dried to obtain a powder material. The powder material is then kept at 500°C for 2 hours to obtain a silicon-carbon anode material for lithium batteries.

[0067] The lithium-ion battery silicon-carbon anode material prepared in this embodiment is used as the anode active material to prepare anode sheets, which are then assembled into button cells in a casing and tested. The specific process is as follows.

[0068] The lithium-ion battery silicon-carbon anode material, acetylene black, and carboxymethyl cellulose (CMC) obtained in this embodiment were thoroughly ground in a mortar at a mass ratio of 9:0.5:0.5. Deionized water was then added, and the mixture was pulped in a pulping machine to form a slurry. This slurry was then coated onto a copper foil current collector and dried in a vacuum oven at 85°C for 10 hours. The dried electrode was then cut into 14mm diameter discs to serve as the anode plates for the lithium-ion battery.

[0069] The electrolyte for assembling the lithium-ion coin cell is 1 mol / L lithium hexafluorophosphate (LiPF6). The solvents in the electrolyte are ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DMC, and DEC of 1:1:1. The separator is a polyethylene membrane. The negative electrode is used as the working electrode, and the counter electrode of the coin cell is a lithium sheet.

[0070] The electrochemical performance of the battery was evaluated using the Blue Battery Testing System. The test conditions were: voltage window of 0.01V-2V; discharge rate of 0.1C; lower limit of discharge voltage window: 0.01V.

[0071] First-week expansion rate test method: At room temperature, the prepared negative electrode sheet is cut by ion beam, and the cross-section is photographed using a scanning electron microscope (SEM). The thickness of the negative electrode sheet is measured and recorded as T1, and the thickness of the copper foil current collector substrate is measured and recorded as T2. Under a current density of 0.1C and a charging cutoff voltage of 2V, the coin cell half-cell is fully charged. Then, the battery is disassembled in a glove box, the negative electrode sheet is removed, and after ion beam cutting, the cross-section is photographed again using SEM, and the thickness of the negative electrode sheet at this time is measured and recorded as T3. Then, the first-week expansion rate is calculated using the formula: First-week expansion rate = [(T3-T1) / (T1-T2)] × 100%.

[0072] The first-cycle expansion rate of the prepared coin cell was obtained through the above tests, and the first-cycle efficiency of the half cell at 0.8V (abbreviated as 0.8V first efficiency) and the capacity retention rate after 200 cycles were obtained through cycle tests according to conventional methods. The results are listed in Table 1.

[0073] Example 2

[0074] This embodiment is used to prepare silicon-carbon anode materials for lithium batteries.

[0075] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0076] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into the vapor deposition furnace and the gas is continuously introduced for 10 minutes to perform silicon deposition.

[0077] S3, at 550℃, a mixture of acetylene and nitrogen in a volume ratio of 5:18 is introduced into the deposition furnace and the gas is continuously introduced for 10 minutes to carry out interlayer deposition of carbon layers.

[0078] Repeat steps S2 and S3 three times to obtain a silicon-carbon composite material with a sandwich structure pre-coated.

[0079] S4. The obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixed gas of acetylene and nitrogen in a ratio of 16:30. The coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained.

[0080] S5. The silicon-carbon composite material and tetraethyl silicate are mixed at a mass ratio of 100:5, and the mixture is spray-dried to obtain a powder material. The powder material is then kept at 500°C for 2 hours to obtain a silicon-carbon anode material for lithium batteries.

[0081] Example 3

[0082] This embodiment is used to prepare silicon-carbon anode materials for lithium batteries.

[0083] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0084] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into the vapor deposition furnace and the gas is continuously introduced for 10 minutes to perform silicon deposition.

[0085] S3, at 550℃, a mixture of acetylene and nitrogen in a volume ratio of 5:18 is introduced into the deposition furnace and the gas is continuously introduced for 10 minutes to carry out interlayer deposition of carbon layers.

[0086] Repeat steps S2 and S3 three times to obtain a silicon-carbon composite material with a sandwich structure pre-coated.

[0087] S4. The obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixed gas of acetylene and nitrogen in a ratio of 16:30. The coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained.

[0088] S5. The silicon-carbon composite material and tetraethyl silicate are mixed at a mass ratio of 100:1 and spray-dried to obtain a powder material. The obtained powder material is then kept at 500℃ for 2 hours to obtain a silicon-carbon anode material for lithium batteries.

[0089] Example 4

[0090] This embodiment is used to prepare silicon-carbon anode materials for lithium batteries.

[0091] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0092] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into the vapor deposition furnace and the gas is continuously introduced for 10 minutes to perform silicon deposition.

[0093] S3, at 550℃, a mixture of acetylene and nitrogen in a volume ratio of 5:18 is introduced into the deposition furnace and the gas is continuously introduced for 10 minutes to carry out interlayer deposition of carbon layers.

[0094] Repeat steps S2 and S3 three times to obtain a silicon-carbon composite material with a sandwich structure pre-coated.

[0095] S4. The obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixed gas of acetylene and nitrogen in a ratio of 16:30. The coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained.

[0096] S5. The silicon-carbon composite material and tetraethyl silicate are mixed at a mass ratio of 100:1 and spray-dried to obtain a powder material. The obtained powder material is then kept at 600℃ for 2 hours to obtain a silicon-carbon anode material for lithium batteries.

[0097] Comparative Example 1

[0098] This comparative example is used to prepare silicon-carbon anode materials for lithium batteries.

[0099] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0100] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into the vapor deposition furnace and the gas is continuously introduced for 10 minutes to perform silicon deposition.

[0101] S3, at 550℃, a mixture of acetylene and nitrogen in a volume ratio of 5:18 is introduced into the deposition furnace and the gas is continuously introduced for 10 minutes to carry out interlayer deposition of carbon layers.

[0102] Repeat steps S2 and S3 three times to obtain a silicon-carbon composite material with a sandwich structure pre-coated.

[0103] S4. The obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixture of acetylene and nitrogen in a ratio of 16:30. The coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained, which is the silicon-carbon composite material of Comparative Example 1.

[0104] Comparative Example 2

[0105] This comparative example is used to prepare silicon-carbon anode materials for lithium batteries.

[0106] S1, under a nitrogen atmosphere, 5 kg of porous carbon is placed in a deposition furnace and heated to 550°C;

[0107] S2, at 550℃, a mixture of silane and nitrogen in a volume ratio of 16:30 is introduced into a vapor deposition furnace and the gas is continuously introduced for 10 minutes to deposit silicon and form a silicon-carbon composite material.

[0108] S3, the obtained silicon-carbon composite material was subjected to carbon coating treatment in a mixed gas of acetylene and nitrogen in a ratio of 16:30, the coating temperature was 550℃, the heating rate was 5℃ / min, the holding time was 4 hours, and after cooling to room temperature, a silicon-carbon composite material with a carbon coating layer was obtained.

[0109] S4. The silicon-carbon composite material and tetraethyl silicate are mixed at a mass ratio of 100:3, and the mixture is spray-dried to obtain a powder material. The powder material is then kept at 500°C for 2 hours to obtain a silicon-carbon anode material for lithium batteries.

[0110]

[0111]

[0112] Table 1

[0113] As can be seen from the data in Table 1, the capacity retention rate, first-cycle expansion rate, and 0.8V first-cycle efficiency of the silicon-carbon composite material prepared in this invention are significantly improved compared to the comparative example after 200 cycles. This indicates that alternating deposition of silicon and carbon on a porous carbon matrix using vapor deposition to form a sandwich structure, and constructing a silicon-oxygen coating layer on the surface of the silicon-carbon composite material using a silane coupling agent, can effectively improve the performance of the material and the battery.

[0114] This invention employs vapor deposition to alternately deposit silicon and carbon on a porous carbon matrix to form a sandwich structure, and then uses a silane coupling agent to construct a silicon-oxygen coating layer on the surface of the silicon-carbon composite material. The carbon sandwich provides mechanical support to a certain extent, buffering the expansion forces caused by volume changes in silicon during charging and discharging, thus extending the material's lifespan. The carbon layer acts as a conductive network, improving electron transport efficiency between silicon particles and enhancing the overall conductivity of the negative electrode. The carbon sandwich restricts the silicon deposition range, reducing particle size and ensuring uniform distribution, thereby improving electrochemical performance. The stability of the surface silicon-oxygen coating layer inhibits the growth of the solid electrolyte interphase (SEI) film, reducing irreversible capacity loss. The silicon-oxygen coating layer reduces direct contact between silicon particles and the electrolyte, minimizing side reactions. Furthermore, the polarity of the silicon-oxygen layer enhances the wettability of the electrolyte on the negative electrode surface, improving the battery's electrochemical performance. The silicon-carbon negative electrode material prepared by this invention exhibits advantages such as high first-cycle efficiency and long cycle life.

[0115] 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 for lithium batteries, characterized in that, The preparation method includes: Step 1: Under a protective atmosphere, place the porous carbon matrix into a vapor deposition furnace; Step 2: Introduce the first mixture of silicon source gas and protective gas to perform silicon deposition; Step 3: Introduce a second mixture of carbon source gas and protective gas to perform interlayer deposition of carbon layer; Step 4: Repeat steps 2 and 3 1-5 times to form a silicon-carbon composite material with a sandwich structure pre-coated. Step 5: Perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating to obtain a silicon-carbon composite material with carbon coating layer. Step 6: The silicon-carbon composite material with carbon coating is mixed evenly in a solution containing silane coupling agent and then spray-dried. The spray-dried material is then heat-treated to obtain the lithium battery silicon-carbon anode material.

2. The preparation method according to claim 1, characterized in that, The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

3. The preparation method according to claim 1, characterized in that, The porous carbon matrix has a particle size D50 of 4-20 μm and a pore size of less than or equal to 4 nm; the micropores account for 10%-100% of the porous carbon matrix.

4. The preparation method according to claim 1, characterized in that, In the first mixed gas, the volume ratio of the silicon source gas to the protective gas is [2-23]:30; The silicon source gas includes one or more of the following: silane, disilane, trichlorosilane, and silicon tetrachloride; The protective gas includes: nitrogen and / or argon; The silicon deposition temperature is 400-800℃ and the time is 10-160 min.

5. The preparation method according to claim 1, characterized in that, In the second mixture, the volume ratio of the carbon source gas to the protective gas is [2-6]:18; The carbon source gas includes one or more of acetylene, methane, and propylene. The protective gas includes: nitrogen and / or argon; The carbon layer is deposited at a temperature of 400-800℃ for 10-120 minutes.

6. The preparation method according to claim 1, characterized in that, The silicon-carbon composite material with a sandwich structure pre-coated by carbon coating treatment is specifically described as follows: The carbon source gas and protective gas are introduced at a volume ratio of [2-30]:30, and the mixture is kept at 400-800℃ for 2-10 hours to perform carbon coating treatment on the silicon-carbon composite material with sandwich structure pre-coating. The coated carbon source gas includes one or more of the following: acetylene, ethylene, propylene, methane, and carbon dioxide; The protective gas includes nitrogen and / or argon.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the silicon-carbon composite material with carbon coating to the silane coupling group is 100:1-100:10; The heat treatment is performed at a temperature of 500-600℃ for a time of 10-160 minutes.

8. A silicon-carbon anode material for lithium batteries prepared by any of the preparation methods of claims 1-7.

9. A lithium battery negative electrode, characterized in that, The lithium battery anode comprises the lithium battery silicon-carbon anode material as described in claim 8.

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

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