Silicon-carbon negative electrode material and preparation method thereof

Abstract

The invention provides a silicon-carbon negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion battery negative electrode materials. The invention discloses a preparation method of a silicon-carbon negative electrode material. The preparation method comprises the following steps: S1, dispersing a matrix material in a solvent to obtain a matrix material solution; s2, adding an organic matter into the matrix material solution, uniformly mixing, carrying out hydrothermal treatment, and carrying out vacuum drying to obtain a surface modified matrix material; s3, performing silicon deposition and passivation treatment on the surface modified matrix material to obtain a nano silicon-based composite material; and S4, coating the nanometer silicon-based composite material with a conductive layer to obtain the silicon-carbon negative electrode material. The silicon-carbon negative electrode material provided by the invention is low in gas production rate and excellent in rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a silicon-carbon negative electrode material and a preparation method thereof. Background Art

[0002] In recent years, people have put forward higher and higher requirements for battery life, safety, fast charging and other performance, and in the future, energy replenishment / charging time may be the main direction affecting the terminal consumer experience. Silicon-based negative electrode materials are considered to be new high-performance lithium-ion battery negative electrode materials due to their high specific capacity, good safety, and abundant sources. In particular, new silicon-carbon materials have become a hot spot for the research and development of silicon negative electrodes due to their low expansion and good cycle life, and are called the third-generation silicon negative materials. Silicon negative electrode materials can provide channels for lithium ion embedding and extraction from all directions. By storing lithium in a smaller volume, the thinner silicon negative electrode allows lithium ions to reach the negative electrode particles faster and easier, which can achieve faster charging speeds. However, the disadvantages of the new silicon-carbon are large specific surface area and high resistivity, which requires secondary coating. However, secondary coating will not only cause excessive growth of silicon grains, but also affect the rate of lithium ion deintercalation when the coating is too thick, and the capacity will also be reduced; but when the coating is less, it cannot effectively reduce the specific surface area and improve the conductivity, which is a major obstacle for the fast charging system, especially for the battery system that wants to use the high gram capacity of silicon to obtain low surface density, so as to achieve both high energy and low internal resistance fast charging design. The resistivity problem of silicon-carbon materials needs to be solved urgently. Therefore, it is urgent to develop a silicon-carbon negative electrode material, which is of great significance to the development of lithium-ion batteries. Summary of the invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a silicon-carbon negative electrode material and a preparation method thereof.

[0004] The present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the following steps:

[0005] S1, dispersing the matrix material in a solvent to obtain a matrix material solution;

[0006] S2, adding organic matter to the matrix material solution, mixing evenly, performing hydrothermal treatment, and vacuum drying to obtain a surface-modified matrix material;

[0007] S3, subjecting the surface-modified matrix material to silicon deposition and passivation treatment to obtain a nano-silicon-based composite material;

[0008] S4. Coating the nano-silicon-based composite material with a conductive layer to obtain a silicon-carbon negative electrode material.

[0009] The present invention selects a highly conductive porous matrix material, modifies it with specific functional groups, and then deposits nano-silicon on the porous conductive matrix by vacuum negative pressure plasma vapor deposition, so that the functional groups on the surface of the matrix material react with the hydroxyl groups on the silicon surface to form chemical bonds, so that the silicon can be more firmly adhered to the conductive matrix material, and the nano-silicon plays an "anchoring" role. Even after high friction and high shear during slurry mixing, it will not fall off, which greatly improves the processing performance of silicon-carbon negative electrode materials. Passivation treatment helps to protect the exposed silicon. Finally, it is coated with a conductive layer, which is a doped conductive polymer film. Even if it is a thin film, it has very good conductivity, and the thinner coating layer is also conducive to increasing the lithium ion deintercalation rate. The new silicon-carbon material prepared by the present invention has significantly improved ionic conductivity and electronic conductivity, so it can take into account the dual needs of energy density and fast charging of the battery cell.

[0010] Preferably, in S1, the matrix material is selected from one or more of MXene, graphene, and black phosphorus.

[0011] The matrix material is made of graphene and graphene-like porous materials, which have excellent conductivity and are easy to be modified with functional groups on the surface. After reacting with the hydroxyl groups on the silicon surface, the silicon is deposited more firmly, which greatly improves the processing performance of silicon and significantly reduces the gas production of the slurry.

[0012] Preferably, in S1, the solvent is selected from one or more of ethanol and water.

[0013] Preferably, in S2, the temperature of the hydrothermal treatment is 160-200° C., and the time of the hydrothermal treatment is 8-20 h.

[0014] Controlling the temperature and time of hydrothermal treatment is helpful to modify the surface functional groups of porous matrix materials.

[0015] Preferably, in said S2, the organic matter contains sulfonic acid and / or carboxyl functional groups.

[0016] More preferably, in S2, the organic matter is selected from one or more of poly(biphenyloxadiazole) and carboxylic acid.

[0017] By selecting organic species for functional group modification, the surface of the base material is enriched with sulfonic acid groups and carboxyl groups, making it easy for silicon to be deposited.

[0018] Preferably, in S3, the deposition treatment includes using a vacuum negative pressure plasma vapor deposition method to decompose the silicon source gas and deposit it on the surface modified base material.

[0019] The use of vacuum negative pressure plasma vapor deposition can significantly promote chemical reactions, allowing deposition to be carried out at a lower temperature, avoiding excessive growth of silicon grains, and making the deposition effect more uniform. A gradient deposit layer is obtained by controlling the gas composition and the air intake rate, that is, reducing the deposition rate at the end of the deposition to avoid a large amount of silicon being deposited outside the pore structure.

[0020] More preferably, in S3, the silicon source gas is selected from one or more of silane, disilane, trisilane and tetrasilane.

[0021] More preferably, in said S3, the deposition amount is 40-60wt% and the deposition temperature is 300-500°C.

[0022] Preferably, in S3, the passivation treatment comprises introducing ammonia gas for 1-5 hours to form a passivation layer; the passivation layer is silicon nitride SiNx, and the thickness of the passivation layer is less than 1 μm.

[0023] Passivation treatment is performed to prevent the high activity reaction of silicon from affecting the material properties. The passivation treatment forms a silicon nitride (SiNx) passivation deposition layer, which not only provides mechanical protection to ensure the structural integrity of silicon and inhibits the excess formation of SEI, but also the fast ion conduction Li3N generated in situ by the lithiation of the active SiNx promotes the transmission of Li ions and achieves fast charging.

[0024] Preferably, in S4, the conductive layer coating comprises coating the nano-silicon-based composite material with an iodine-doped polyacetylene conductive material; specifically comprising: mixing the iodine-doped polyacetylene conductive material with the nano-silicon-based composite material, introducing argon protective gas, and achieving uniform coating of the conductive layer through a dynamic solid phase reaction, wherein the coating temperature is 400-600°C, the coating time is 1-4h, and the coating amount is 1-3wt%.

[0025] The conductive coating layer uses iodine-doped polyacetylene conductive material, which has a conductivity 7 orders of magnitude higher than that of ordinary carbon materials. The conductive layer film is relatively thin (<1μm), which is conducive to better lithium ion deintercalation, thus taking into account both ionic conductivity and electronic conductivity.

[0026] The present invention also provides a silicon-carbon negative electrode material prepared by the above preparation method.

[0027] The beneficial effects of the present invention are:

[0028] The present invention selects a highly conductive porous matrix material, modifies it with specific functional groups, and then deposits nano-silicon on the porous conductive matrix by vacuum negative pressure plasma vapor deposition. The functional groups on the surface of the matrix material react with the hydroxyl groups on the silicon surface to form chemical bonds, so that silicon can be more firmly adhered to the conductive matrix material, and the nano-silicon plays an "anchoring" role. Even after high friction and high shear during slurry mixing, it will not fall off, greatly improving the processing performance of silicon carbon. At the same time, in the later stage of silicon deposition, on the one hand, the deposition rate is slowed down to avoid a large amount of silicon deposition outside the pore structure, and on the other hand, the exposed silicon is protected by depositing a silicon nitride passivation layer. Finally, it is coated with a conductive layer, which is a doped conductive polymer film. Even if it is a thin film, it has very good conductivity, and the thinner coating layer is also conducive to improving the lithium ion deintercalation rate. The ionic conductivity and electronic conductivity of the new silicon-carbon material prepared by the present invention are significantly improved, so it can take into account the dual needs of the energy density and fast charging of the battery cell at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a 7-day gas production curve of the slurry of Comparative Example 1 and Example 1 proposed by the present invention.

[0030] Figure 2 It is a constant current charging ratio curve diagram of the soft-pack batteries of Comparative Example 2 and Example 2 charged at different rates. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described in detail through specific embodiments.

[0032] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0033] Example 1

[0034] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0035] S1, dispersing 100 g of graphene material in ethanol to obtain a graphene solution;

[0036] S2, adding 5g of poly(biphenyloxadiazole) to the graphene solution, mixing evenly, and then transferring to a hydrothermal reactor, reacting at 180°C for 12h, taking out the material after natural cooling, and vacuum drying to obtain a surface-modified matrix material;

[0037] S3, placing the surface modified matrix material into a vapor deposition equipment furnace, introducing silane and argon (intake ratio 1:1), the inlet rate 0.3L / min, the deposition temperature 450°C, after deposition for 6 hours, reducing the inlet rate to 0.1L / min, and introducing a small amount of NH3, and ending the ventilation after 2 hours to obtain a nano-silicon-based composite material;

[0038] S4, introducing argon protective gas, adding 1wt% of iodine-doped polyacetylene conductive material to the nano-silicon-based composite material for solid phase dynamic conductive layer coating, the coating temperature is 500°C, and after coating for 2h, a silicon-carbon negative electrode material is obtained.

[0039] Example 2

[0040] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0041] S1. Dispersing 100 g of MXene material in deionized water to obtain a MXene solution;

[0042] S2. Add 10 mL of acetic acid to the MXene solution, mix well, and transfer to a hydrothermal reactor. React at 160° C. for 8 h. After natural cooling, take out the material and vacuum dry it to obtain a surface-modified matrix material.

[0043] S3, placing the surface modified matrix material into a vapor deposition equipment furnace, introducing silane and argon (intake ratio 1:1.5), an intake rate of 0.5L / min, a deposition temperature of 300°C, and after deposition for 10 hours, reducing the intake rate to 0.2L / min, and introducing a small amount of NH3, and ending the ventilation after 2 hours to obtain a nano-silicon-based composite material;

[0044] S4, introducing argon protective gas, adding 3wt% of iodine-doped polyacetylene conductive material to the nano-silicon-based composite material for solid phase dynamic conductive layer coating, the coating temperature is 600° C., and after coating for 1.5 hours, a silicon-carbon negative electrode material is obtained.

[0045] Comparative Example 1

[0046] A method for preparing a silicon-carbon negative electrode material comprises the following steps:

[0047] S1. 100 g of commercially available resin-based porous carbon matrix material: Sinosteel CQ-20 resin-based porous carbon matrix material was placed in a vapor deposition equipment furnace, and silane and argon (gas inlet ratio 1:1) were introduced at a gas inlet rate of 0.3 L / min and a deposition temperature of 450° C. After deposition for 6 h, a nano-silicon-based composite material was obtained;

[0048] S2. Pass argon protective gas, add 1wt% iodine-doped polyacetylene conductive material to the nano-silicon-based composite material for solid phase dynamic conductive layer coating, the coating temperature is 500° C., and after coating for 2 hours, a silicon-carbon negative electrode material is obtained.

[0049] Comparative Example 2

[0050] The only difference between Comparative Example 2 and Example 2 is that the MXene material is replaced with a conventional porous carbon matrix: Yuanli SDPC-G1 petroleum coke-based porous carbon matrix, and other conditions remain unchanged.

[0051] The silicon-carbon negative electrode material prepared in Example 1 and Comparative Example 1, as well as the conductive agent, binder, etc., were added to a slurry mixing tank, and slurried in a ratio of silicon: SP: SWCNT: PAA = 60: 10: 10: 20, and dry mixed, kneaded, and then the viscosity was adjusted; the solid content was controlled to be 15%, the viscosity was 8000 mpas, and stirred to obtain a uniformly dispersed silicon negative electrode slurry; about 30 g of the homogenized slurry was taken and sealed in an aluminum-plastic film bag, and allowed to stand at room temperature for 7 days, and the gas production volume was tested by the drainage method. The test results are as follows: Figure 1 The silicon-carbon negative electrode materials prepared in Example 2 and Comparative Example 2 were made into negative electrode sheets, assembled into soft-pack batteries, and tested for high-rate fast charging performance. The test results are shown in Figure 2 shown.

[0052] Figure 1 This is a 7-day gas production curve of the slurry of Comparative Example 1 and Example 1. It can be seen that the silicon-carbon negative electrode material prepared by the present invention produces 0.12 mL of gas after slurry mixing for 7 days, which means that basically no gas is produced, while the material of Comparative Example 1 produces 2.65 mL of gas for 7 days, and the gas production is significantly higher than the silicon-carbon negative electrode material of the present invention.

[0053] Figure 2 The constant current charging ratio curves of the soft-pack batteries of Example 2 and Example 2 at different charging rates are compared. It can be seen that the 3C charging constant current charging ratio of the soft-pack of Example 2 is 76.8%, while the 3C charging constant current charging ratio of the soft-pack of Comparative Example 2 is only 49.3%. It can be seen that the rate performance of the silicon-carbon negative electrode material of the present invention has been significantly improved.

[0054] In summary, the silicon-carbon negative electrode material provided by the present invention has low gas production and excellent rate performance.

[0055] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized in that: The following steps are involved: S1, dispersing the matrix material in a solvent to obtain a matrix material solution; S2, adding organic matter to the matrix material solution, mixing evenly, performing hydrothermal treatment, and vacuum drying to obtain a surface-modified matrix material; S3, subjecting the surface-modified matrix material to silicon deposition and passivation treatment to obtain a nano-silicon-based composite material; S4. Coating the nano-silicon-based composite material with a conductive layer to obtain a silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: In the S1, the matrix material is selected from one or more of MXene, graphene, and black phosphorus.

3. The preparation method according to claim 1, characterized in that: In the S2, the temperature of the hydrothermal treatment is 160-200° C., and the time of the hydrothermal treatment is 8-20 hours.

4. The preparation method according to claim 1, characterized in that: In the S2, the organic matter is selected from one or more of poly(biphenyloxadiazole) and carboxylic acid.

5. The preparation method according to claim 1, characterized in that: In the above-mentioned S3, the deposition process includes using a vacuum negative pressure plasma vapor deposition method to decompose the silicon source gas and deposit it on the surface modified base material.

6. The preparation method according to claim 1, characterized in that: In the above-mentioned S3, the passivation treatment includes introducing ammonia gas for 1-5 hours to form a passivation layer.

7. The preparation method according to claim 1, characterized in that: In the above-mentioned S4, the conductive layer coating includes coating the nano-silicon-based composite material with a conductive layer by using an iodine-doped polyacetylene conductive material.

8. A silicon-carbon negative electrode material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

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