Uniform nanoscale carbon-coated graphite negative electrode material and preparation method thereof

Abstract

The invention discloses a preparation method of a uniform nanoscale carbon-coated graphite negative electrode material, which comprises the following steps of: growing a thin and uniform silicon dioxide nano layer on the surface of a graphite particle in a liquid phase, coating carbon on the surface of the silicon dioxide-coated graphite particle, and removing the silicon dioxide layer through alkaline etching to obtain the uniform nanoscale carbon-coated graphite negative electrode material. Therefore, the carbon-coated graphite negative electrode material with uniform nanoscale thickness can be obtained, and the volume expansion resistance of the material is improved.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in consumer electronics, new energy vehicles and large-scale energy storage due to their high operating voltage, high energy density and long cycle life. Negative electrode materials are one of the four key materials for lithium-ion batteries, which are mainly divided into two categories: carbon materials and non-carbon materials. Graphite in carbon materials can be specifically divided into natural graphite and artificial graphite. Natural graphite has the advantages of low cost and high specific capacity, while artificial graphite has better cycle performance, safety performance and charge and discharge rate performance. In addition, its raw material sources are extensive and its technology and industry supporting facilities are mature. It is currently the mainstream negative electrode material for lithium-ion batteries.

[0003] Currently, the negative electrode materials on the market are mainly artificial graphite, and the surface coating materials are soft carbon / hard carbon materials. The soft carbon or hard carbon coated on the surface of artificial graphite has low specific capacity and low first efficiency. One of the measures to improve the first efficiency of the material is to coat the graphite surface with carbon-based / non-carbon-based materials with high first efficiency and good kinetics without reducing the energy density of the material.

[0004] The raw materials of artificial graphite are mainly petroleum coke and needle coke. After processes such as crushing, grading and graphitization, single-particle negative electrode materials can be obtained, which have high specific capacity and good cycle performance. However, due to the different orientation degrees of single particles in various directions, there are still certain defects in its electrochemical performance, such as low first coulombic efficiency and poor rate performance, which are not conducive to its industrial application. Therefore, it is necessary to improve its preparation process to improve the processing performance, first coulombic efficiency and rate performance of the negative electrode material.

[0005] As lithium-ion batteries have higher requirements for negative electrode energy density, negative electrode materials are required to have high specific capacity while also improving the initial efficiency of the material, and improving the full battery positive electrode capacity and energy density. At present, the modification technology of carbon-based negative electrode materials mainly uses multiphase coating technology to coat the surface to construct a core-shell structure, doping, surface oxidation, etc., to improve electrochemical performance. Traditional liquid phase carbon coating has problems such as uneven coating thickness and easy collapse in the subsequent carbonization process, which seriously affects the performance of graphite negative electrodes. Summary of the invention

[0006] The main purpose of the present invention is to provide a uniform nano-scale carbon-coated graphite negative electrode material and a preparation method thereof, so as to enhance the conductivity of the graphite negative electrode, improve the rate performance and the initial efficiency.

[0007] To achieve the above object, the present invention provides a method for preparing a uniform nanoscale carbon-coated graphite negative electrode material, comprising the steps of:

[0008] S1, growing a silicon dioxide layer on the surface of a powdered graphite material by liquid phase growth to obtain a silicon dioxide-coated graphite material;

[0009] S2, carbon-coating the surface of the silica-coated graphite material obtained in step S1 to obtain a carbon-coated graphite material;

[0010] S3, performing alkaline etching on the carbon-coated graphite material obtained in step S2 to remove the silicon dioxide layer, thereby obtaining a uniform nanoscale carbon-coated graphite negative electrode material.

[0011] Furthermore, the graphite material in step S1 is one or more of natural flake graphite, microcrystalline graphite, crystalline vein graphite, artificial graphite, natural spherical graphite, mesophase carbon microspheres, conductive graphite, graphene and graphite fiber.

[0012] Furthermore, the thickness of the silicon dioxide layer in step S1 is controlled to be 50-500 nanometers.

[0013] Furthermore, the liquid phase growth method in step S1 includes: adding isopropanol to the graphite material, and after stirring and mixing thoroughly by ultrasonic dispersion, adding water, ammonia water and tetraethyl silicate, continuing to stir until thoroughly mixed, heating the mixture at 35-45°C and maintaining it for 1.5-2.5h, and the reaction is completed to obtain a silica-coated graphite material.

[0014] Furthermore, before step S1, the method further includes the steps of cleaning and roughening the graphite material.

[0015] Furthermore, the carbon coating method in the above step S2 includes: grinding and mixing the silica-coated graphite material and cyclopentadienyl nickel in a ratio of 0.-1.2:1, and then annealing at 550-650°C in an inert atmosphere, and washing the obtained product with HCL to obtain a carbon-coated graphite material, wherein the outer carbon layer is an amorphous carbon layer.

[0016] Furthermore, the alkaline etching method in step S3 is to remove the silicon dioxide layer by using NaOH or NH4OH.

[0017] The present invention also provides a uniform nano-scale carbon-coated graphite negative electrode material, which is prepared by any of the preparation methods described above.

[0018] The present invention also provides a negative electrode current collector for a lithium ion battery, the negative electrode current collector comprising: a conductive substrate and a negative electrode slurry layer coated on one or both sides of the conductive substrate, the negative electrode slurry layer being prepared by any of the preparation methods described above.

[0019] The present invention further provides a lithium ion battery, comprising a positive electrode, an electrolyte and a negative electrode, characterized in that the negative electrode comprises the lithium ion battery negative electrode collector as described above.

[0020] Compared with the prior art, the present invention first grows a thin and uniform silicon dioxide nanolayer on the surface of graphite particles in liquid phase, then performs carbon coating on the surface of the silicon dioxide-coated graphite particles, and then removes the silicon dioxide layer by alkaline etching, thereby obtaining a carbon-coated graphite negative electrode material with uniform nanometer-level thickness, and the material's resistance to volume expansion is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1 This is the SEM image of the graphite in Comparative Example 1 that is not carbon-coated.

[0023] Figure 2 This is the SEM image of the surface-coated silica graphite in Comparative Example 2.

[0024] Figure 3 This is a SEM picture of the graphite in Example 1 in which the surface of the graphite is coated with silicon dioxide and then carbon-coated, and then the silicon dioxide layer is removed by alkaline etching. DETAILED DESCRIPTION

[0025] The technical solution in this embodiment will be described clearly and completely below in conjunction with the drawings in this embodiment. Obviously, the described embodiment is only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0027] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0028] Comparative Example 1

[0029] Artificial graphite with a carbon content of more than 85% and a particle size of 3 to 40 μm.

[0030] Comparative Example 2

[0031] 0.15 g of the artificial graphite in Comparative Example 1 was added with 190 ml of isopropanol, and the mixture was thoroughly mixed by ultrasonic dispersion for 30 min and stirring for 30 min. Then, 1 ml of water and 10 ml of 25% ammonia water were added, and 0.2 ml of tetraethyl silicate was slowly dropped into the mixture. The mixture was stirred until thoroughly mixed, and the mixture was heated at 40°C for 2 h. After the reaction was completed, the mixture was filtered and dried to obtain a silica-coated graphite material.

[0032] Example 1

[0033] 0.15 g of the artificial graphite in Comparative Example 1 was added with 190 ml of isopropanol, and the mixture was thoroughly mixed by ultrasonic dispersion for 30 min and stirring for 30 min. Then, 1 ml of water and 10 ml of 25% ammonia water were added, and 0.2 ml of tetraethyl silicate was slowly dropped into the mixture. The mixture was stirred until thoroughly mixed, and the mixture was heated at 40°C for 2 h. After the reaction was completed, the mixture was filtered and dried to obtain a silica-coated graphite material.

[0034] 10 g of the silica-coated graphite material obtained in the above step was mixed with cyclopentadienyl nickel in a ratio of 1:1 at a speed of 800 r / min for 10 min, and then annealed at 600° C. for 2 h in an inert atmosphere. The obtained product was pickled with HCL to obtain a carbon-coated graphite material, and the outer carbon layer was an amorphous carbon layer.

[0035] The carbon-coated graphite material was alkaline-etched with a 2 mol / L NaOH solution to remove the silicon dioxide layer, thereby obtaining a uniform nanoscale carbon-coated graphite negative electrode material.

[0036] Please combine Figure 1-3 It can be seen that carbon is coated on the surface of silica-coated graphite. The SEM of the carbon-coated graphite negative electrode material after alkaline etching to remove the silica layer shows that after silica pre-coating treatment, the surface carbon coating is more uniform and smooth, and no Si component is obtained after EDS scanning, indicating that the silica has been completely etched away.

[0037] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a uniform nanoscale carbon-coated graphite negative electrode material, characterized in that: Includes steps: S1, growing a silicon dioxide layer on the surface of a powdered graphite material by liquid phase growth to obtain a silicon dioxide-coated graphite material; S2, carbon-coating the surface of the silica-coated graphite material obtained in step S1 to obtain a carbon-coated graphite material; S3, performing alkaline etching on the carbon-coated graphite material obtained in step S2 to remove the silicon dioxide layer, thereby obtaining a uniform nanoscale carbon-coated graphite negative electrode material.

2. The method according to claim 1, characterized in that The graphite material in step S1 is one or more of natural flake graphite, microcrystalline graphite, crystalline vein graphite, artificial graphite, natural spherical graphite, mesophase carbon microspheres, conductive graphite, graphene and graphite fiber.

3. The method according to claim 1, characterized in that The thickness of the silicon dioxide layer in step S1 is controlled to be 50-500 nanometers.

4. The method according to claim 1, characterized in that: The liquid phase growth method in step S1 includes: adding isopropanol to the graphite material, and stirring and mixing thoroughly by ultrasonic dispersion, adding water, ammonia water and tetraethyl silicate, continuing to stir until thoroughly mixed, heating the mixture at 35-45°C for 1.5-2.5h, filtering and drying after the reaction is completed, and obtaining a silica-coated graphite material.

5. The method according to claim 4, characterized in that Before step S1, the method further includes the steps of cleaning and roughening the graphite material.

6. The method according to claim 5, characterized in that The carbon coating method in the above step S2 includes: grinding and mixing the silica-coated graphite material and cyclopentadienyl nickel in a ratio of 0.-1.2:1, and then annealing at 550-650°C in an inert atmosphere, and washing the obtained product with HCL to obtain a carbon-coated graphite material, wherein the outer carbon layer is an amorphous carbon layer.

7. The method according to claim 4, characterized in that The alkaline etching method in step S3 is to remove the silicon dioxide layer by using NaOH or NH4OH.

8. A uniform nanoscale carbon-coated graphite negative electrode material, characterized in that: The method is prepared according to any one of claims 1 to 8.

9. A negative electrode current collector for a lithium ion battery, characterized in that: The negative electrode current collector comprises: a conductive substrate and a negative electrode slurry layer coated on one side or both sides of the conductive substrate, wherein the negative electrode slurry layer is prepared by the preparation method according to any one of claims 1 to 7.

10. A lithium ion battery comprising a positive electrode, an electrolyte and a negative electrode, characterized in that: The negative electrode comprises the negative electrode current collector of the lithium ion battery as claimed in claim 9.

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