A method for preparing graphene and fluorinated graphene

Abstract

The application relates to a method for preparing fluorinated graphene, and belongs to the graphene material field. The preparation method comprises the following steps: mixing and dispersing waste lithium battery recovery graphite powder, an intercalation agent and a dispersing agent in water to form a slurry, keeping the slurry at 40-60 DEG C for 4-8 hours, then spraying the slurry through a high-pressure device to form high-speed jets, and realizing graphite layer peeling through the cross impact of multiple jet beams, then adding a fluorination agent, keeping the slurry at 150-200 DEG C for 6-12 hours, centrifugally separating upper clear liquid, filtering and washing, vacuum drying, and obtaining fluorinated graphene. The application realizes graphite layer peeling through liquid cross impact, has high production efficiency, the obtained graphene sheet layer is regular and neat, has few structural defects, and the performance of the graphene is improved; the peeling strength can be adjusted by adjusting the jet speed, different layer number graphene products can be obtained, and the production is continuous, and the efficiency is relatively high; the raw material is waste lithium battery recovery graphite, the cost is low, the obtained graphene contains oxygen-containing functional groups, and has good water solubility.

Description

A method for preparing graphene and fluorinated graphene Technical Field

[0001] This invention belongs to the field of graphene materials, specifically relating to a method for preparing graphene and fluorinated graphene. Background Technology

[0002] Because fluorinated graphene retains the two-dimensional structure of graphene and its chemical composition is similar to that of polytetrafluoroethylene (PTFE), it possesses properties similar to both two-dimensional graphene and PTFE. Like PTFE, fluorinated graphene exhibits particularly outstanding insulation properties, hydrophobicity, chemical stability, and solvent resistance, and also possesses a certain degree of high-temperature resistance, only beginning to slowly decompose at temperatures above 260°C. Furthermore, due to the presence of CF bonds on its surface, fluorinated graphene is difficult to react with other substances, thus exhibiting good performance stability and anti-aging properties, making it exceptionally advantageous in electrical insulation materials. Therefore, fluorinated graphene has broad application prospects in fields such as cathode materials, lubricants, and insulating materials, and can be used in electronic devices such as transistors and displays. In recent years, it has attracted increasing attention from scholars both domestically and internationally and has experienced rapid development.

[0003] Currently, fluorinated graphene is prepared from fluorinated graphite using ultrasonic, solvothermal, or mechanical exfoliation methods. Fluorinated graphene prepared by ultrasonic or solvothermal methods maintains a large specific surface area and good conductivity, and has a wider range of applications. However, the exfoliation force is insufficient, and the exfoliation effect is poor for graphite sheets that are too thick, resulting in low yield. Mechanical exfoliation has a large impact force, which causes structural defects in the graphene layer, reduces the size of the exfoliated graphene, and makes it difficult to obtain large-size, high-quality graphene.

[0004] Patent CN114014308A mentions that an aqueous suspension of dispersant and nano-inorganic materials is prepared, and layered graphite is added to the aqueous suspension to obtain a layered graphite suspension. The suspension is then sheared and dispersed, and a nano-inorganic material and graphene aqueous dispersion is obtained by high-pressure micro-jet homogeneous impact. According to "Analysis of the Ultrafine Grinding Mechanism of Micro-Jet Homogenizer" (Food and Machinery, May 2009, Vol. 25, No. 3, p. 66), the working principle of the micro-jet homogenizer is as follows: a high-pressure suspension of material is injected into a valve body with an aperture of tens to hundreds of micrometers. A huge pressure gradient is generated before and after the valve inlet, causing the suspended material to be subjected to high-speed shearing, achieving the initial pulverization purpose. After passing through the valve orifice, the material forms a high-speed jet at subsonic or supersonic speeds. At the valve outlet, due to the velocity difference and turbulence, the material is further broken down. When the high-speed jet collides at high speed with a diamond target plate or a jet in the opposite direction, target impact pulverization is formed, enhancing the pulverization effect and completing the ultrafine pulverization of suspended particles in the material. There are two types of jet impact: one is impacting the target plate, and the other is opposing jets. When producing graphene using patent CN114014308A, if an impact target is used, the graphite particles will make hard contact with the diamond target, and the graphene sheet structure will still be destroyed. If the opposite direction of the jet is used, that is, countercurrent jetting, the front jet impacts and reflects severely, offsetting the velocity of the subsequent jet. The subsequent jet is decelerated a lot, and the impact force is not very large, so the graphite exfoliation effect is not optimal.

[0005] It is also understood that the recycling and reuse of waste lithium batteries is a new industry advocated and encouraged by the government, and it is also a new research hotspot for many universities and enterprises. If the graphite powder recycled from waste lithium batteries is to be used to manufacture lithium batteries again, it needs to undergo impurity removal, regeneration, and modification treatments. These treatments are very costly, and how to utilize this graphite powder at low cost is a challenge for the industry. Summary of the Invention

[0006] To overcome the above shortcomings, the present invention first adopts the following technical solution:

[0007] A method for preparing graphene is provided, wherein graphite powder is mixed with intercalating agent and dispersant and dispersed in water to form a slurry, kept at 40-60℃ for 4-8 hours, and then sprayed by a high-pressure device to form a high-speed jet. Multiple jets collide to achieve graphite layer exfoliation. The supernatant is separated by centrifugation, filtered and washed, and vacuum dried to obtain graphene.

[0008] The graphite powder is obtained from the recycling of waste lithium-ion batteries. It is inexpensive. Due to the numerous lithium-ion insertion and extraction processes, the graphite particles have many cracks, increased interlayer spacing, and weakened interlayer bonding, making it easier for intercalating agents to insert between graphite layers. For ease of spraying, the particle size is preferably 1–40 μm. Graphite from recycled waste batteries is unsuitable for direct use in lithium battery manufacturing due to impurities and structural defects. Its application requires complex processing and is costly. However, using it to prepare graphene turns these disadvantages into advantages.

[0009] The graphite recycled from the waste lithium battery contains a large number of oxygen-containing functional groups, resulting in graphene with good water solubility.

[0010] The intercalating agent is selected from at least one of ammonium carbonate, ammonium oxalate, potassium carbonate, potassium sulfate, and ammonium sulfate.

[0011] The dispersant is selected from at least one of sodium carboxymethyl cellulose (CMC), sodium dodecylbenzene sulfonate (SDBS), and polyvinylpyrrolidone (PVP).

[0012] The weight ratio of the graphite powder to the intercalating agent and dispersant is 1:(1-5):(0.05-0.1).

[0013] The slurry has a solid content of 2-10% and a viscosity of 50-1000 mPa·s. If the solid content is too high, the impact effect will be poor and the peeling ratio will be low. If the solid content is too low, the production efficiency will be reduced.

[0014] The high-speed jet velocity is 200-500 m / s, and the angle between any two jets is between 45° and 135°. If the angle is too small, the jets are nearly in the same direction, resulting in poor impact. If the angle is too large, the jets are nearly in opposite directions, leading to severe deceleration and also poor impact. Because the jet velocity gradually decreases as it advances, the velocity before impact is no less than 200 m / s.

[0015] The pressure and orifice diameter of the high-pressure jetting device are not specifically limited, as long as the jet velocity meets the requirements.

[0016] Preferably, the spraying is carried out in a sealed cavity, and the cavity is evacuated, which reduces the resistance of the liquid flow and improves the impact effect.

[0017] More preferably, the liquid collected inside the cavity is returned to the high-pressure jetting device for repeated jetting impact, thereby increasing the peeling effect.

[0018] The solid residue obtained from centrifugation can be returned as a graphite raw material, thus making full use of the raw materials.

[0019] Based on the above-mentioned method for preparing graphene, the present invention also provides a method for preparing fluorinated graphene, wherein graphite powder is mixed with an intercalating agent and a dispersant and dispersed in water to form a slurry, which is kept at 40-60°C for 4-8 hours, and then sprayed by a high-pressure device to form a high-speed jet. Multiple jets collide to achieve graphite layer exfoliation. Then, a fluorinating agent is added and kept at 150-200°C for 6-12 hours. The supernatant is separated by centrifugation, filtered and washed, and vacuum dried to obtain fluorinated graphene.

[0020] Preferably, the fluorinating agent is selected from at least one of hydrogen fluoride, ammonium hydrogen fluoride, sodium hydrogen fluoride, and potassium hydrogen fluoride, and the amount of fluorinating agent used is 0.5-5 times the weight of graphite powder.

[0021] The beneficial effects of this invention are as follows: This invention uses cross-flow impact rather than reverse impact to achieve graphite layer exfoliation, resulting in high production efficiency. It also avoids the damage to the graphene structure caused by the mechanical shearing forces of ball milling and grinding, leading to regular and neat graphene sheets with fewer structural defects and improved graphene performance. The exfoliation strength can be controlled by adjusting the jet velocity to obtain graphene products with different numbers of layers, and continuous production is highly efficient. The raw material used is recycled graphite from waste lithium batteries, resulting in low cost. The produced graphene contains oxygen-containing functional groups and has good water solubility. Attached Figure Description

[0022] Figure 1 is an electron microscope image of the fluorinated graphene product obtained in Example 1.

[0023] Figure 2 is an electron microscope image of the fluorinated graphene product obtained in Example 2.

[0024] Figure 3 is an electron microscope image of the fluorinated graphene product obtained in Example 3.

[0025] Figure 4 is an electron microscope image of the fluorinated graphene product obtained in Example 4.

[0026] Figure 5 is an electron microscope image of the fluorinated graphene product obtained in Example 5.

[0027] Figure 6 is a schematic diagram of jet impact in Example 1.

[0028] Figure 7 is a schematic diagram of jet impact in Example 3.

[0029] In Figures 6 and 7: 1 represents the slurry, 2 represents the booster pump, 3 represents the ejector, and 4 represents the jet impact zone. Detailed Implementation

[0030] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The pressure on the inner wall of the high-pressure jetting device is 10-100MPa, and the nozzle diameter is adjustable within the range of 0.1-2.0mm.

[0031] Example 1

[0032] A method for preparing fluorinated graphene includes the following steps:

[0033] 800g of recycled graphite powder from waste lithium batteries was mixed with 1600g of ammonium carbonate and 50g of CMC and dispersed in 40kg of water to form a slurry with a viscosity of 270mPa·s. The slurry was kept at 50℃ for 6h and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 0.2mm, a pressure of 40MPa, and a jet velocity of 300m / s. The two jets collided perpendicularly to achieve graphite layer exfoliation. The jetting was circulated for 300min. Then, 400g of liquid hydrogen fluoride was added, stirred evenly, and kept at 185℃ for 8h. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 925g of fluorinated graphene (fluorine content 39%, estimated graphene mass before fluorination was 564g, yield 70.5%). More than 80% of the graphene sheets had a diameter greater than 200nm.

[0034] Example 2

[0035] A method for preparing fluorinated graphene includes the following steps:

[0036] 2000g of recycled graphite powder from waste lithium batteries was mixed with 10000g of ammonium sulfate and 200g of SDBS and dispersed in 110kg of water to form a slurry with a viscosity of 530mPa·s. The slurry was kept at 60℃ for 4h and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 0.5mm, a pressure of 90MPa, and a jet velocity of 400m / s. The three jets collided perpendicularly to achieve graphite layer exfoliation. The process was repeated for 120min. Then, 2000g of ammonium bifluoride powder was added, stirred evenly, and kept at 200℃ for 6h. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 2249g of fluorinated graphene (fluorine content 28%, estimated graphene mass before fluorination was 1619g, yield 81.0%). More than 80% of the graphene sheets had a diameter greater than 200nm, and the number of graphene layers was mainly 1-5.

[0037] Example 3

[0038] A method for preparing fluorinated graphene includes the following steps:

[0039] 1000g of recycled graphite powder from waste lithium batteries was mixed with 1000g of ammonium oxalate and 80g of PVP and dispersed in 100kg of water to form a slurry with a viscosity of 80mPa·s. The slurry was kept at 40℃ for 8h and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 0.7mm, a pressure of 20MPa, and a jet velocity of 200m / s. Three jets collided, with any two jets having an angle of 120° to achieve graphite layer exfoliation. The jetting was cyclically sprayed for 120min. Then, 3000g of sodium hydrogen fluoride powder was added, stirred evenly, and kept at 150℃ for 12h. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 1377g of fluorinated graphene (fluorine content 56%, estimated graphene mass before fluorination 606g, yield 60.6%). More than 80% of the graphene sheets had a diameter greater than 200nm, and the number of graphene layers was mainly 5-9.

[0040] Example 4

[0041] A method for preparing graphene includes the following steps:

[0042] 800g of recycled graphite powder from waste lithium batteries was mixed with 2000g of ammonium carbonate and 60g of CMC and dispersed in 40kg of water to form a slurry with a viscosity of 300mPa·s. The slurry was kept at 55℃ for 6 hours and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 0.3mm, a pressure of 40MPa, and a jet velocity of 320m / s. The two jets collided at a 100° angle to achieve graphite layer exfoliation. The process was repeated for 120 minutes. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 615g of graphene, with a yield of 76.9%.

[0043] Example 5

[0044] A method for preparing graphene includes the following steps:

[0045] 2000g of recycled graphite powder from waste lithium batteries was mixed with 8000g of ammonium sulfate and 160g of SDBS and dispersed in 110kg of water to form a slurry with a viscosity of 480mPa·s. The slurry was kept at 58℃ for 4h and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 0.5mm, a pressure of 90MPa, and a jet velocity of 350m / s. Three jets collided at angles of 90°, 90°, and 120° to achieve graphite layer exfoliation. The process was repeated for 120min. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 1596g of graphene, with a yield of 79.8%.

[0046] Example 6

[0047] A method for preparing graphene includes the following steps:

[0048] 1000g of recycled graphite powder from waste lithium batteries was mixed with 1500g of ammonium oxalate and 80g of PVP and dispersed in 100kg of water to form a slurry with a viscosity of 80mPa·s. The slurry was kept at 40℃ for 8h and then sprayed through a high-pressure device to form a high-speed jet with an aperture of 1.0mm, a pressure of 20MPa, and a jet velocity of 260m / s. Any two of the three jets collided at an angle of 60° and any two jets collided at an angle of 120° to achieve graphite layer exfoliation. The process was repeated for 60min. The supernatant was separated by centrifugation, filtered, washed, and vacuum dried to obtain 648g of graphene, with a yield of 67.8%.

[0049] Comparative Example 1

[0050] The process was basically the same as in Example 4, except that the jet angle was changed to 180°, which means that the two jets collided in opposite directions. The process was repeated for 120 minutes, and after centrifugation, filtration and drying, 386g of graphene was obtained, with a yield of 48.3%.

[0051] Comparative Example 2

[0052] The process was basically the same as in Example 4, except that the jet velocity was changed to 140 m / s and the jet was circulated for 120 min. After centrifugation and filtration, no graphene product was obtained.

[0053] Comparative Example 3

[0054] The process was basically the same as in Example 4, except that the raw materials were changed to ordinary natural graphite. After 120 minutes of cyclic spraying, centrifugation, filtration and drying were performed to obtain 21g of graphene, with a yield of 2.6%.

[0055] In Comparative Example 1, the jet angle was large, resulting in poor stripping effect and low product yield. In Comparative Example 2, the jet velocity was low, resulting in almost no stripping. In Comparative Example 3, no graphite recycled from waste lithium batteries was used, so the stripping effect was also very poor, and the product yield was very low.

[0056] To facilitate comparison of the experimental data, the results are summarized in the table below:

[0057]

[0058]

Claims

1. A method for preparing graphene, characterized in that, Graphite powder is mixed with intercalating agent and dispersant and dispersed in water to form a slurry. The slurry is kept at 40-60℃ for 4-8 hours, and then sprayed through a high-pressure device to form a high-speed jet. Multiple jets collide and achieve graphite layer exfoliation. The supernatant is separated by centrifugation, filtered, washed, and vacuum dried to obtain graphene. The graphite powder is obtained by recycling waste lithium-ion batteries. The velocity of the high-speed jet is 200-500 m / s, and the angle between any two jets is between 45 and 135°. The velocity of the jet before impact is not less than 200 m / s.

2. The method for preparing graphene according to claim 1, characterized in that, The graphite powder has a particle size of 1–40 μm.

3. The method for preparing graphene according to claim 1, characterized in that, The intercalating agent is selected from at least one of ammonium carbonate, ammonium oxalate, potassium carbonate, potassium sulfate, and ammonium sulfate.

4. The method for preparing graphene according to claim 1, characterized in that, The dispersant is selected from at least one of sodium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, and polyvinylpyrrolidone.

5. The method for preparing graphene according to claim 1, characterized in that, The weight ratio of the graphite powder to the intercalating agent and dispersant is 1:(1-5):(0.05-0.1).

6. The method for preparing graphene according to claim 1, characterized in that, The slurry has a solid content of 2-10% and a viscosity of 50-1000 mPa·s.

7. A method for preparing fluorinated graphene, characterized in that, According to any one of claims 1-6, a fluorinating agent is added between the steps of graphite layer exfoliation and centrifugation, the mixture is kept at 150-200℃ for 6-12 hours, and then the supernatant is separated by centrifugation, filtered and washed, and vacuum dried to obtain fluorinated graphene.

8. The method for preparing fluorinated graphene according to claim 7, characterized in that, The fluorinating agent is selected from at least one of hydrogen fluoride, ammonium hydrogen fluoride, sodium hydrogen fluoride, and potassium hydrogen fluoride, and the amount of fluorinating agent used is 0.5-5 times the weight of graphite powder.

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