Method for modifying recycled graphite by deep impurity removal and asphalt coating

Abstract

The application provides a method for regenerating graphite, deeply removing impurities and modifying pitch coating, which comprises the following steps: adding regenerated graphite into a dilute sulfuric acid solution, stirring and reacting, performing suction filtration on the obtained regenerated graphite after impurities are removed, washing the regenerated graphite until neutral and drying; mixing pitch and tetrahydrofuran, obtaining pitch suspension after ultrasonic dispersion, adding the regenerated graphite after impurities are removed into the pitch suspension, drying after mixing and stirring for a certain time, and obtaining a mixture; carbonizing the mixture in an inert atmosphere in sections, then washing, drying and obtaining regenerated graphite after impurities are deeply removed. The method can reduce the total residual metal impurities of the regenerated graphite by a large margin through mild deep impurity removal with dilute sulfuric acid, and does not damage the graphite crystal lattice. The method can repair surface cracks and defects and reduce interface impedance by coating the regenerated graphite with pitch. The method can improve the electrochemical performance of the regenerated graphite by combining deep impurity removal with pitch coating.

Description

Technical Field

[0001] This invention relates to the field of recycled graphite production technology, and in particular to a method for deep impurity removal and bitumen coating modification of recycled graphite. Background Technology

[0002] The scale of retired lithium-ion batteries in my country is growing rapidly, with graphite anodes accounting for 12-21 wt%, indicating huge potential for resource utilization. Traditional wet recycling methods result in graphite leaching residue containing metallic impurities and electrolyte residues. Furthermore, the surface contains numerous oxygen-containing functional groups, damaging the graphite structure and causing poor interlayer conductivity, making it unsuitable for direct use as a battery anode. Conventional acid washing tends to over-etch the graphite structure, and high-concentration coating increases lithium-ion transport resistance. Currently, a process that combines gentle impurity removal with precise coating is lacking. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a method for the deep purification and pitch coating modification of recycled graphite, which can gently remove impurities from recycled graphite and improve its electrochemical performance.

[0004] One embodiment of the present invention provides a method for deep impurity removal and bitumen coating modification of recycled graphite, comprising the following steps: S1. Add the recycled graphite to a dilute sulfuric acid solution, stir and react, then filter the purified recycled graphite, wash it with water until neutral and dry it. S2. Mix asphalt with tetrahydrofuran, disperse by ultrasonication to obtain asphalt suspension, add purified recycled graphite to asphalt suspension, mix and stir for a certain time and then dry to obtain mixture material; S3. The mixture is carbonized in stages under an inert atmosphere, then washed with water and dried to obtain deeply purified recycled graphite.

[0005] In some embodiments, in step S1, before adding the recycled graphite to the dilute sulfuric acid solution, the recycled graphite is first ball-milled, sieved to a particle size of 10~50 μm, and vacuum-dried to a moisture content of ≤0.5%.

[0006] In some embodiments, in step S1, the liquid-solid ratio of the dilute sulfuric acid solution to the recycled graphite is 8:1 to 15:1.

[0007] In some embodiments, in step S1, the concentration of the dilute sulfuric acid solution is 0.05~0.5 M.

[0008] In some embodiments, in step S1, the reaction temperature of the dilute sulfuric acid solution with the recycled graphite is 40~60 °C, and the reaction time is 30~60 min.

[0009] In some embodiments, in step S1, the drying temperature is 60~80 ℃, and the drying method is vacuum drying.

[0010] In some embodiments, in step S2, the temperature for mixing and stirring the asphalt suspension and recycled graphite is 80~95 ℃, the stirring speed is 200~400 rpm, and the stirring time is 1~3 h.

[0011] In some embodiments, step S3, the segmented carbonization method includes: holding at 300~400 ℃ for 0.5~1 h in an inert atmosphere, then holding at 700~900 ℃ for 1~3 h, and then naturally cooling.

[0012] In some embodiments, in step S3, the inert atmosphere is a nitrogen atmosphere.

[0013] Another embodiment of the present invention provides a recycled graphite prepared by the above method, characterized in that it is used to prepare a negative electrode material for lithium-ion batteries. Attached Figure Description

[0014] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 A flowchart illustrating the method for deep impurity removal and bitumen coating modification of recycled graphite according to an embodiment of the present invention; Detailed Implementation Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0015] The following describes, with reference to the accompanying drawings, a method for deep impurity removal and bitumen coating modification of recycled graphite according to embodiments of the present invention.

[0016] like Figure 1 As shown, one embodiment of the present invention proposes a method for deep impurity removal and bitumen coating modification of recycled graphite, comprising the following steps: S1. Add the recycled graphite to a dilute sulfuric acid solution, stir and react, then filter the purified recycled graphite, wash it with water until neutral and dry it. S2. Mix asphalt with tetrahydrofuran, disperse by ultrasonication to obtain asphalt suspension, add purified recycled graphite to asphalt suspension, mix and stir for a certain time and then dry to obtain mixture material; S3. The mixture is carbonized in stages under an inert atmosphere, then washed with water to remove trace amounts of impurities containing Na, Cl, and Al, and then vacuum dried to obtain deeply purified recycled graphite.

[0017] This invention employs dilute sulfuric acid for gentle, deep impurity removal, ensuring that the total residual metallic impurities in the recycled graphite are ≤0.004 μg / g without damaging the graphite lattice. Coating the recycled graphite with pitch creates a uniform carbon layer, repairing surface cracks and defects and reducing interfacial impedance. Combining deep impurity removal with pitch coating improves the electrochemical performance of the recycled graphite, achieving an initial discharge specific capacity ≥330 mAh / g, an initial coulombic efficiency ≥98.5%, and significantly enhanced rate performance and cycle stability. The method described in this invention is environmentally friendly, using low-concentration acid, containing no toxic reagents, and its waste is easily treated, making it suitable for industrial application.

[0018] Furthermore, in step S1, the water washing method is as follows: deionized water is used to wash until the pH of the filtrate is 6-7.

[0019] In some embodiments, in step S1, before adding the recycled graphite to the dilute sulfuric acid solution, the recycled graphite is first ball-milled, sieved to a particle size of 10~50 μm, and vacuum-dried to a moisture content of ≤0.5%. This allows impurities in the recycled graphite to be exposed on the surface to the greatest extent, improving the impurity removal rate.

[0020] In some embodiments, in step S1, the liquid-solid ratio of the dilute sulfuric acid solution to the recycled graphite is 8:1 to 15:1.

[0021] In some embodiments, in step S1, the concentration of the dilute sulfuric acid solution is 0.05~0.5 M, preferably 0.1 M.

[0022] In some embodiments, in step S1, the reaction temperature of the dilute sulfuric acid solution with the recycled graphite is 40~60 ℃, preferably 60 ℃, and the reaction time is 30~60 min, preferably 50 min.

[0023] In some embodiments, in step S1, the drying temperature is 60~80 ℃, and the drying method is vacuum drying.

[0024] In some embodiments, in step S2, the temperature for mixing and stirring the asphalt suspension and recycled graphite is 80-95 °C, the stirring speed is 200-400 rpm, and the stirring time is 1-3 h. This results in an asphalt coating amount of 3%-10%, preferably 5%.

[0025] Furthermore, in step S2, the drying temperature is 100 ℃.

[0026] In some embodiments, the segmented carbonization method in step S3 includes: holding at 300~400 °C for 0.5~1 h in an inert atmosphere, then holding at 700~900 °C for 1~3 h, preferably holding at 800 °C for 2 h, and then naturally cooling.

[0027] In some embodiments, in step S3, the inert atmosphere is a nitrogen atmosphere.

[0028] Furthermore, in step S3, the carbonization process is carried out in a tubular furnace.

[0029] Another embodiment of the present invention provides a recycled graphite prepared by the above method, characterized in that it is used to prepare a negative electrode material for lithium-ion batteries.

[0030] The present invention will be further illustrated by specific embodiments below.

[0031] Example 1 A method for deep impurity removal and bitumen coating modification of recycled graphite includes the following steps: S1. Take 5 g of regenerated graphite by Joule flash evaporation at 2200 ℃, pass it through a 50 μm sieve, dry it at 80 ℃, add 0.1 M dilute sulfuric acid solution, the liquid-solid ratio of dilute sulfuric acid solution to regenerated graphite is 10:1, stir at 60 ℃ for 50 min, filter the obtained purified regenerated graphite, wash it with water until neutral, and dry it.

[0032] S2. Dissolve 0.25 g of asphalt in 100 mL of tetrahydrofuran and sonicate for 30 min to obtain an asphalt suspension. Add the purified recycled graphite obtained in step S1 to the asphalt suspension, stir at 90 ℃ and 300 rpm for 2 h, and dry at 100 ℃ to obtain a mixture with an asphalt coating of 5%.

[0033] S3. The obtained mixture is carbonized in stages under N2 atmosphere, kept at 350 ℃ for 0.5 h, then kept at 800 ℃ for 2 h, then washed with deionized water and vacuum dried to obtain battery-grade recycled graphite.

[0034] Performance testing: The initial discharge specific capacity is 332.19 mAh / g, the coulombic efficiency is 98.62%, and the capacity retention rate after 200 cycles is 98.7%.

[0035] Comparative Example 1 The difference from Example 1 is that the impurity removal with dilute sulfuric acid is not performed, and the asphalt coating step is performed directly.

[0036] Performance testing: The obtained recycled graphite has a high impurity content, large polarization, an initial discharge specific capacity of 266 mAh / g, and rapid cycle decay.

[0037] Comparative Example 2 The difference from Example 1 is as follows: In step S2, the stirring temperature was 85 ℃, lower than 90 ℃ in Example 1, which reduced the asphalt dispersion fluidity and increased the adhesion and deposition thickness. The stirring speed was 220 rpm, lower than 300 rpm in Example 1, which weakened shear dispersion and prevented the asphalt from becoming overly dispersed and thin. The stirring time was 3 h, longer than 2 h in Example 1, which extended the time for asphalt to adsorb and deposit on the graphite particle surface. Ultimately, the asphalt coating amount was 10%. This is because the low temperature, low speed, and long stirring time reduced the uniformity of asphalt dispersion, resulting in a large amount of asphalt being enriched and deposited on the graphite particle surface.

[0038] In step S3, the carbonization is carried out in stages under N2 atmosphere protection, and the temperature is maintained at 350 °C for 0.5 h, and then maintained at 820 °C for 2.5 h, which is slightly higher than 800 °C in Example 1, to adapt to the complete carbonization of the thick carbon layer.

[0039] Performance testing: A thicker asphalt layer will further clog the pores between graphite layers, increasing the resistance to lithium-ion diffusion; the low-rate capacity increases slightly, but the high-rate performance decreases, the cycle polarization continues to increase, and the capacity retention rate after 200 cycles decreases.

[0040] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0044] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0045] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for deep impurity removal and bitumen coating modification of recycled graphite, characterized in that, Includes the following steps: S1. Add the recycled graphite to a dilute sulfuric acid solution, stir and react, then filter the purified recycled graphite, wash it with water until neutral and dry it. S2. Mix asphalt with tetrahydrofuran, disperse by ultrasonication to obtain asphalt suspension, add the purified recycled graphite to the asphalt suspension, mix and stir for a certain time, and then dry to obtain a mixture. S3. The mixture is carbonized in stages under an inert atmosphere, then washed with water and dried to obtain deeply purified recycled graphite.

2. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S1, before adding the recycled graphite to the dilute sulfuric acid solution, the recycled graphite is first ball-milled, sieved to a particle size of 10~50 μm, and vacuum-dried to a moisture content of ≤0.5%.

3. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S1, the liquid-to-solid ratio of the dilute sulfuric acid solution to the recycled graphite is 8:1 to 15:

1.

4. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S1, the concentration of the dilute sulfuric acid solution is 0.05~0.5 M.

5. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S1, the reaction temperature between the dilute sulfuric acid solution and the recycled graphite is 40~60 ℃, and the reaction time is 30~60 min.

6. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S1, the drying temperature is 60~80 ℃, and the drying method is vacuum drying.

7. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S2, the temperature for mixing the asphalt suspension and the recycled graphite is 80~95 ℃, the stirring speed is 200~400 rpm, and the stirring time is 1~3 h.

8. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S3, the segmented carbonization method includes: holding at 300~400 ℃ for 0.5~1 h under the inert atmosphere, then holding at 700~900 ℃ for 1~3 h, and then naturally cooling.

9. The method for deep impurity removal and bitumen coating modification of recycled graphite according to claim 1, characterized in that, In step S3, the inert atmosphere is a nitrogen atmosphere.

10. A recycled graphite prepared by the method according to any one of claims 1 to 9, characterized in that, Used to prepare negative electrode materials for lithium-ion batteries.

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