Preparation method of high-magnification graphite composite material

Abstract

The invention discloses a preparation method of a high-magnification graphite composite material, which comprises the following steps: crushing a coke raw material, mixing the crushed coke raw material with carbon nanotubes, pre-carbonizing, graphitizing to obtain a carbon nanotube doped graphite material, etching the surface of the carbon nanotube doped graphite material by concentrated nitric acid steam, washing with deionized water until the carbon nanotube doped graphite material is neutral, and carrying out vacuum drying to obtain the high-magnification graphite composite material. The porous carbon nanotube doped graphite material is obtained, and the amorphous carbon / lithium coated carbon nanotube doped graphite composite material is obtained through gradient deposition of metal lithium and amorphous carbon. The electron and ion conductivity of the material can be improved, and the rate capability, the high-temperature performance and the energy density can be improved.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically a method for preparing high-ratio graphite composite materials. Background Technology

[0002] With the increasing market demand for fast charging of lithium-ion batteries, the anode materials used must not only possess fast charging performance but also ensure high-temperature performance. Currently, measures to improve the fast charging performance of anode materials mainly include reducing particle size, increasing coating amount, or doping with heteroatoms to improve the electronic or ionic conductivity of the material. However, reducing particle size will reduce the energy density of the material, and increasing coating amount will reduce the high-temperature performance of the material, making it difficult to simultaneously achieve good rate performance, energy density, and high-temperature performance. Although some studies have improved the lithium-ion diffusion rate and rate performance by coating the material surface with inorganic lithium compounds, this will reduce its energy density. For example, Chinese patent application No. 202111331207.3 discloses a fast-charging graphite composite material and its preparation method. The composite material is a composite composed of small-particle graphite and solid electrolyte, and an inorganic lithium salt is coated on its outer surface to obtain the graphite composite material. Although the initial efficiency of the material is improved, the bonding force deviation between the inorganic lithium salt coating layer and the core results in a limited improvement in fast charging performance and a decrease in energy density and high-temperature performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a method for preparing high-rate graphite composite materials that can improve the electronic and ionic conductivity of materials, improve rate performance, high-temperature performance, and energy density.

[0004] The present invention provides a method for preparing a high-ratio graphite composite material, comprising the following steps: Step S1: According to the mass ratio of coke raw material: carbon nanotubes = 100: 1-5, the coke raw material is crushed to 10μm and mixed with carbon nanotubes. Then, it is pre-carbonized at 700-900℃ for 2-12h, and then graphitized at 2800-3200℃ for 12-48h to obtain carbon nanotube-doped graphite material. Step S2: Transfer the carbon nanotube-doped graphite material to a three-necked flask and pass concentrated nitric acid vapor (65% by mass) through it. Etch the material by passing it through at a flow rate of 100-500 SCCM for 60-600 min. Wash the resulting material three times with deionized water until it is neutral and then vacuum dry it to obtain porous carbon nanotube-doped graphite material. Step S3: Transfer the porous carbon nanotube-doped graphite material to a vacuum furnace, then heat it to 850-950℃ and introduce lithium hydride gas at a flow rate of 10-100 SCCM for 30-300 min. Then change the volume ratio to carbon source gas: heteroatom gas = 10:1-5 and introduce it at a flow rate of 10-100 SCCM for 30-300 min. This is one cycle, and the deposition is carried out for 1-10 weeks to obtain the final product.

[0005] In the above-mentioned method for preparing a high-ratio graphite composite material, the coke raw material in step S1 is one of petroleum coke, needle coke, or pitch coke.

[0006] In the above-mentioned method for preparing a high-ratio graphite composite material, the carbon source gas in step S3 is one of methane, ethane, ethylene, or acetylene; the heteroatom gas is one of ammonia, hydrogen boroide, or hydrogen sulfide. Compared with existing technologies, this invention has significant advantages. As can be seen from the above technical solutions: This invention improves the electronic conductivity of coke raw materials by doping them with carbon nanotubes, and increases active sites through surface etching, thereby enhancing the material's kinetic properties and surface pore formation, and improving its liquid retention performance. Through vapor deposition, metallic lithium and amorphous carbon are sequentially deposited on the surface of porous carbon nanotube-doped graphite material to improve the material's electronic conductivity and reduce defects in the porous material, thus improving the initial efficiency. Simultaneously, the use of vapor deposition offers advantages such as good deposition uniformity, high density, and process controllability. Furthermore, the deposition of amorphous carbon on the outermost layer isolates the core metallic lithium from direct contact with the electrolyte, reducing side reactions and gas production, and improving storage and cycling performance. Attached Figure Description

[0007] Figure 1 This is a comparison chart of the constant current ratio between the example and the comparative example. Detailed Implementation

[0008] The following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of the method for preparing a high-ratio graphite composite material proposed in this invention: Example 1: A method for preparing a high-ratio graphite composite material includes the following steps: Step S1: 100g of needle coke was pulverized to 10μm and mixed with 3g of carbon nanotubes. The mixture was then pre-carbonized at 800℃ for 6h, and then graphitized at 3000℃ for 24h to obtain carbon nanotube-doped graphite material. Step S2: Transfer the carbon nanotube-doped graphite material to a three-necked flask and pass concentrated nitric acid vapor (65% by mass) through it. Etch the material at a flow rate of 300 SCCM for 300 min. Wash the resulting material three times with deionized water until neutral and vacuum dry at 80℃ for 24 h to obtain porous carbon nanotube-doped graphite material. Step S3: Transfer the porous carbon nanotube-doped graphite material to a vacuum furnace, then heat it to 900°C and introduce lithium hydride gas at a flow rate of 50 SCCM for 150 min. Then, change the flow rate to carbon source / heteroatom gas with a volume ratio of ethylene gas: ammonia gas = 10:3 and introduce it at a flow rate of 50 SCCM for 150 min. This is one cycle, and the deposition is carried out for 5 weeks to obtain the final product.

[0009] Example 2: A method for preparing a high-ratio graphite composite material includes the following steps: Step S1: After crushing 100g of petroleum coke raw material to 10μm, mix it with 1g of carbon nanotubes and pre-carbonize it at 700℃ for 12h, then heat it to 2800℃ for graphitization for 48h to obtain carbon nanotube-doped graphite material. Step S2: Transfer the carbon nanotube-doped graphite material to a three-necked flask and pass concentrated nitric acid vapor (65% by mass) through it. Etch the material at a flow rate of 100 SCCM for 600 min. Wash the resulting material three times with deionized water until neutral and vacuum dry at 80°C for 24 h to obtain porous carbon nanotube-doped graphite material. Step S3: Transfer the porous carbon nanotube-doped graphite material to a vacuum furnace, then heat it to 850°C and introduce lithium hydride gas at a flow rate of 10 SCCM for 300 min. Then, change the flow rate to a carbon source / heteroatom gas with a volume ratio of acetylene gas:hydrogen boride gas = 10:1 and introduce it at a flow rate of 10 SCCM for 300 min. This completes one cycle, and the deposition is carried out for 10 weeks to obtain the final product.

[0010] Example 3: A method for preparing a high-ratio graphite composite material includes the following steps: Step S1: After pulverizing 100g of pitch coke to 10μm, mix it with 5g of carbon nanotubes and pre-carbonize it at 900℃ for 2h, then raise the temperature to 3200℃ for graphitization for 12h to obtain carbon nanotube-doped graphite material. Step S2: Transfer the carbon nanotube-doped graphite material to a three-necked flask and pass concentrated nitric acid vapor (65% by mass) through it. Etch the material at a flow rate of 500 SCCM for 60 min. Wash the resulting material three times with deionized water until neutral and vacuum dry at 80°C for 24 h to obtain porous carbon nanotube-doped graphite material. Step S3: Transfer the porous carbon nanotube-doped graphite material to a vacuum furnace, then heat it to 950°C and introduce lithium hydride gas at a flow rate of 100 SCCM for 30 min. Then, change the flow rate to a carbon source / heteroatom gas with a volume ratio of methane gas:hydrogen sulfide gas = 10:5 and introduce it at a flow rate of 100 SCCM for 30 min. This completes one cycle and deposition is carried out for one week to obtain the final product.

[0011] Comparative Example 1: A method for preparing a graphite composite material includes: unlike Example 1, concentrated nitric acid etching is not performed, that is, the porous carbon nanotube-doped graphite material in step S3 is replaced with carbon nanotube-graphite material.

[0012] Comparative Example 2: A method for preparing a graphite composite material includes: unlike Example 1, lithium hydride gas is not introduced in step S3, but the rest is the same as in Example 1.

[0013] Experimental Example 1: (1) Physicochemical property testing The tap density and specific surface area of ​​the graphite composite anode materials in Examples 1-3 and Comparative Examples 1-2 were tested according to the test methods in standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The OI value of the powder materials was measured by XRD, and the powder resistivity was measured using a four-probe analyzer. The test results are shown in Table 1.

[0014] Table 1 As can be seen from Table 1, the resistivity of the graphite composite powder prepared in Examples 1-3 is significantly better than that in Comparative Examples 1-2. This may be because the surface of the materials in the examples is coated with metallic lithium, which reduces the resistivity of the powder and increases the tap density of the material.

[0015] (2) Button cell battery test The graphite composite materials obtained in Examples 1-3 and the graphite composite anode materials in Comparative Examples 1-2 were assembled into coin cells according to the following methods: The graphite composite anode materials prepared in Examples 1-3 and Comparative Examples 1-2 were used as anodes and assembled into coin cells with lithium sheets, electrolytes, and separators in a glove box with argon and water contents both below 0.1 ppm. The separator was Celegard 2400; the electrolyte was a LiPF6 solution with a LiPF6 concentration of 1 mol / L, and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) at a weight ratio of 1:1.

[0016] The fabricated coin cells were labeled A-1, B-1, C-1, D-1, and E-1, respectively. Their performance was then tested using a blue-light battery tester under the following conditions: 0.1C charge / discharge rate, voltage range of 0.05-2V, cycling for 3 cycles. Afterwards, the discharge specific capacity under 2C conditions was measured, and the 2C / 0.1C rate performance and cycle performance (25±3℃, 0.2C / 0.2C, 100 cycles) were calculated. The test results are shown in Table 2.

[0017] Table 2 As shown in Table 2, the coin cells made using the graphite composite materials of Examples 1-3 exhibit significantly higher discharge specific capacity and initial efficiency than those of Comparative Examples 1-2. The experimental results demonstrate that the graphite composite material of this invention enables the battery to possess excellent discharge specific capacity and initial efficiency. This is because lithium coating on the graphite surface reduces its irreversible capacity, thereby improving the initial efficiency and specific capacity. Simultaneously, carbon nanotube doping enhances the material's electronic conductivity and specific capacity, thus improving rate performance.

[0018] (3) Performance testing of pouch batteries Using the graphite composite materials of Examples 1-3 and Comparative Examples 1-2 as the negative electrode active material, and the positive electrode active material ternary material (LiNi) 1 / 3 Co 1 / 3 Mn 1 / 3 A 5Ah pouch cell was assembled from O2, electrolyte, and separator. The separator was Celegard 2400, and the electrolyte was a LiPF6 solution (a 1:1 volume ratio mixture of EC and DEC, with a LiPF6 concentration of 1.3 mol / L). The fabricated pouch cells were labeled A-2, B-2, C-2, D-2, and E-2, respectively, and their cycle and rate performance were tested. The test results are detailed in Table 3.

[0019] 4.1 Cyclic performance: The cycle performance of the battery was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3℃. 4.2 Rate performance: The battery is charged to 100% SOC using a constant current + constant voltage mode at a 2C rate. The constant current ratio is then calculated as constant current capacity / (constant current capacity + constant voltage capacity).

[0020] Table 3 Table 3 shows the cycle performance of the soft-pack batteries prepared from the obtained graphite composite material. As can be seen from the table, the cycle performance of the batteries in the examples is significantly better than that of the comparative examples. This is because the lithium coating on the surface of the graphite composite material in the examples reduces lithium ion consumption during charging and discharging, and its high specific surface area improves liquid retention, thus enhancing its cycle performance. Meanwhile, Table 3 and... Figure 1 The figure shows a comparison of the rate performance (constant current ratio) of the materials in the examples. As can be seen from the figure, the battery in the examples has a high constant current ratio. This is because the materials in the examples have low powder resistivity, which improves the rate performance of the materials.

[0021] The above are merely preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from any technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1.A method for preparing a high-rate graphite composite material, comprising the following steps: Step S1: mixing carbon nanotubes with a coke raw material after the coke raw material is crushed to 10 μm at a mass ratio of coke raw material: carbon nanotubes = 100: 1-5, and then pre-carbonizing at a temperature of 700-900 ℃ for 2-12 h, and then graphitizing at a temperature of 2800-3200 ℃ for 12-48 h to obtain a carbon nanotube-doped graphite material; Step S2: transferring the carbon nanotube-doped graphite material into a three-neck flask, and then etching by introducing steam of concentrated nitric acid with a mass concentration of 65% at a flow rate of 100-500 SCCM for 60-600 min, and then washing with deionized water until neutral, and then vacuum drying to obtain a porous carbon nanotube-doped graphite material; Step S3: transferring the porous carbon nanotube-doped graphite material into a vacuum furnace, and then heating to 850-950 ℃ and introducing lithium hydride gas at a flow rate of 10-100 SCCM for 30-300 min, and then introducing carbon source / gas atom gas with a volume ratio of carbon source gas: gas atom gas = 10: 1-5 at a flow rate of 10-100 SCCM for 30-300 min as a cycle period, and then depositing for 1-10 weeks. 2.The method for preparing a high-rate graphite composite material according to claim 1, wherein the coke raw material in step S1 is one of petroleum coke, needle coke or pitch coke. 3.The method for preparing a high-rate graphite composite material according to claim 1, wherein the carbon source gas in step S3 is one of methane, ethane, ethylene or acetylene; and the gas atom gas is one of ammonia, boron hydride or hydrogen sulfide.

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