Sulfonated graphene and modified cathode material, and preparation method and application thereof

Abstract

The application belongs to the field of graphene modification, and particularly relates to sulfonated graphene and modified positive electrode material as well as a preparation method and application thereof. The preparation method of the sulfonated graphene comprises the following steps: S1. Pre-reaction of an organic material and a sulfonating agent in the absence of a reaction medium at 30-35 DEG C to obtain a pre-reaction product; S2. Dispersion of the pre-reaction product in water, and then heating the obtained dispersion to 160-220 DEG C to perform high-pressure hydrothermal reaction to obtain the sulfonated graphene. When the sulfonated graphene obtained by the method provided by the application is used to coat the positive electrode material, the rate performance and cycle performance of the lithium ion battery can be significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of graphene modification, specifically relating to a sulfonated graphene and a modified cathode material, as well as their preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices such as mobile phones, digital cameras, and laptops due to their advantages such as high operating voltage, high specific energy, long lifespan, and no memory effect. They are also widely used in new energy vehicles and energy storage devices as a substitute for petroleum. For lithium-ion batteries, the cathode material not only accounts for the highest proportion of battery cost, but its performance is also a major factor affecting the overall electrochemical performance and safety of the battery. Olivine-type lithium iron phosphate cathode materials have become a hot research and development area worldwide due to their abundant resources, long cycle life, and good safety. They are widely used in new energy vehicles, energy storage devices, uninterruptible power supplies, power tools, and other fields, with a very broad market prospect. Research has found that smaller cathode material particle sizes can minimize mechanical stress and provide better battery cycle performance. When the particle size of lithium iron phosphate decreases from the micrometer level to the nanometer level, the conductivity and diffusion coefficient of the cathode material will increase significantly, even by an order of magnitude, thereby significantly improving battery performance. Therefore, nanoscale cathode material particles will become a trend in the cathode material industry. However, the low conductivity of pure LiFePO4 cathode materials limits their rate capability and cycle performance. To address this issue, LiFePO4 cathode materials are typically modified with carbon coating. The carbon coating layer can improve the conductivity of LiFePO4 cathode materials and isolate the electrolyte, thereby improving the rate performance and cycle performance of lithium-ion batteries.

[0003] Materials used to form carbon coatings include graphene, glucose, and sucrose. Glucose and sucrose, being small organic molecules, are often used as cathode materials for coatings. However, during heat treatment, a large amount of hydrocarbon components in glucose and sucrose escapes in gaseous form, resulting in residual carbon adhering to the cathode material surface in a network or even discontinuous manner. Furthermore, the poor structure of the residual carbon from glucose and sucrose after heat treatment leads to poor conductivity, ultimately affecting the battery's electrochemical performance. While conventional graphene materials possess excellent conductivity, they are prone to agglomeration and difficult to disperse uniformly on the cathode material surface. Using it as a carbon coating material results in a cathode material with strong oxidizing properties at the end of charging, leading to the release of large amounts of oxygen and weakening the battery's rate performance and cycle life. To address this, existing technologies have employed sulfonation modification of graphene to improve its water solubility, thereby enabling more uniform dispersion within the cathode material. Regarding the preparation method of sulfonated graphene, CN105764839A discloses a method for preparing sulfonated graphene from organic materials. This method includes reacting the organic material with an oxidizing sulfonating agent in a reaction medium at a first temperature, and then, in the same reaction medium, raising the reaction temperature to a second temperature to continue the reaction. The first temperature is the melting temperature of the organic material below the boiling point of the reaction medium, and the second temperature is above the boiling point of the reaction medium, thereby obtaining sulfonated graphene. However, when sulfonated graphene obtained by this method is used as a carbon coating material for cathode materials, it cannot significantly improve the rate performance and cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The primary objective of this invention is to overcome the problem that sulfonated graphene prepared using existing methods cannot improve the rate performance and cycle performance of carbon coating materials for cathode materials, and to provide a new method for preparing sulfonated graphene, thereby obtaining sulfonated graphene that can significantly improve the rate performance and cycle performance of lithium-ion batteries.

[0005] Specifically, the method for preparing sulfonated graphene provided by the present invention includes the following steps:

[0006] S1. Organic materials and sulfonating agents are pre-reacted at 30-35°C in the absence of a reactive medium to obtain a pre-reaction product;

[0007] S2. The pre-reaction product is dispersed in water, and the resulting dispersion is heated to 160-220°C for high-pressure hydrothermal reaction to obtain sulfonated graphene.

[0008] A second objective of the present invention is to provide sulfonated graphene prepared by the above method.

[0009] A third objective of this invention is to provide the application of the above-mentioned sulfonated graphene as a carbon material coating agent for cathode materials.

[0010] A fourth objective of the present invention is to provide a modified cathode material, the modified cathode material comprising a cathode material matrix and a coating layer covering the surface of the cathode material matrix, the coating layer being formed from the aforementioned sulfonated graphene.

[0011] The fifth objective of this invention is to provide a method for preparing the above-mentioned modified cathode material. The method includes dispersing the above-mentioned sulfonated graphene in water, mixing the resulting sulfonated graphene dispersion with the cathode material and / or cathode material precursor, and then sequentially filtering, drying and calcining the resulting mixture to obtain the modified cathode material.

[0012] After in-depth and extensive research, the inventors of this invention discovered that the reason why sulfonated graphene obtained by the method disclosed in CN105764839A cannot effectively improve the rate performance and cycle performance of lithium-ion batteries is mainly because: although the sulfonated graphene obtained by this method has good hydrophilicity, its sheet size is too large. When used as a carbon coating material for the cathode material, it forms a garnet-shaped coating, failing to achieve comprehensive and effective coating of the nanoscale cathode material. This results in the inability to form an effective conductive layer on the surface of the cathode material, while part of the cathode material remains exposed in the electrolyte, inevitably failing to improve the rate performance and cycle performance of the lithium-ion battery. Furthermore, the first temperature in CN105764839A generally needs to be at a relatively high temperature to oxidize the organic material into a carbon material such as graphene, accompanied by a small amount of carbon sulfonation, and the formation of larger-scale crystal nuclei, which facilitates the formation of large-diameter graphene sheets at a second, even higher temperature.

[0013] The key to this invention lies in pre-reacting organic materials and sulfonating agents at a lower temperature in the absence of a reactive medium, followed by a high-pressure hydrothermal reaction at a higher temperature using water as a medium. The resulting sulfonated graphene, when used to coat cathode materials, significantly improves the rate performance and cycle performance of lithium-ion batteries. The reason for this is speculated to be that: sulfonates are typically superacids; contacting them with organic materials in a non-reactive medium allows them to densely distribute around the organic materials. The organic materials undergo dehydrogenation condensation and carbonization at a lower temperature using the sulfonating agent as a catalytic medium, initially decomposing into nanoscale carbon flakes. Simultaneously, the lower reaction temperature effectively prevents small-diameter carbon flakes from fusing into larger ones. Dispersing the pre-reaction product in water quenches the further fusion and growth reaction of the small-diameter carbon flakes formed at the lower temperature, ensuring that their size does not increase further. Simultaneously, the sulfonating agent reacts with water to generate sulfuric acid and hydrochloric acid. During the subsequent high-pressure hydrothermal reaction, the mixed acid solution promotes the dehydrogenation condensation and carbonization of residual organic matter in the pre-reaction product, thereby increasing the product yield. The carbon microplates formed at lower temperatures, as well as those formed by the dehydrogenation condensation of residual organic matter in the high-pressure hydrothermal reaction system, undergo a transformation from an amorphous carbon structure to a more crystalline carbon structure. Furthermore, the sulfonic acid groups dissociated from the sulfuric acid in the high-pressure hydrothermal reactor suspend on the surface or edges of the carbon material, forming water-soluble, nanoscale sulfonated graphene with fewer defects. This gives it both the conductivity of graphene and good water solubility, further enhancing the conductivity of the cathode material and providing lithium-ion batteries with excellent rate performance. Moreover, due to the fewer defects in the obtained graphene structure, its conductivity remains at a high level after multiple cycles, contributing to the good cycle performance of lithium-ion batteries. Furthermore, the sulfonated graphene provided by this invention has good water solubility and a nanoscale particle size, which can effectively improve the conductivity of the cathode material, and the cathode material can be effectively coated without subsequent grinding to refine the particle size. In addition, the raw materials for preparing the sulfonated graphene provided by this invention are inexpensive and readily available. Attached Figure Description

[0014] Figure 1 The image shows the Raman spectrum of the sulfonated graphene powder obtained from Preparation Example 1.

[0015] Figure 2 The image shows a scanning electron microscope (SEM) image of the sulfonated graphene powder obtained from Preparation Example 1.

[0016] Figure 3 The infrared spectrum of the sulfonated graphene powder obtained from Example 1 is shown below.

[0017] Figure 4 The image shows the Raman spectrum of the sulfonated graphene powder obtained from Comparative Preparation Example 2. Detailed Implementation

[0018] It should be noted that, in this invention, all numerical values, whether or not explicitly indicated, are defined herein as being modified by the term "about". The term "about" generally refers to a range of numerical values ​​that those skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​within that range and all subranges included within that range.

[0019] The method for preparing sulfonated graphene provided by this invention includes the following steps:

[0020] S1. The organic material and the sulfonating agent are pre-reacted in the absence of a reactive medium to obtain the pre-reaction product;

[0021] S2. The pre-reaction product is dispersed in water, and the resulting dispersion is subjected to high-pressure hydrothermal reaction to obtain sulfonated graphene.

[0022] In this invention, the preferred mass ratio of the organic material to the sulfonating agent is 1:(10-20), specifically 1:10, 1:12, 1:14, 1:16, 1:18, 1:20, or any value between them. The ratio of the organic material to the sulfonating agent can be any value within the above range, and will not be enumerated here.

[0023] This invention does not particularly limit the type of organic material; it can be any existing material capable of carbonizing to generate graphene. It can be a small-molecule organic material, a high-molecular-weight organic material, or a mixture of both. The small-molecule organic material may include at least one of toluene, xylene, styrene, naphthalene, phenylacetylene, n-hexane, and n-octane. The high-molecular-weight organic material may include at least one of polyethylene, polypropylene, polystyrene, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, and cis-butadiene rubber. Polypropylene is particularly preferred. The inventors of this invention have discovered that when polypropylene is used as an organic material, the resulting sulfonated graphene is more beneficial for improving the rate performance and cycle performance of lithium-ion batteries when used to coat and modify the cathode material. The reason for this is speculated to be that polypropylene has a unique carbon chain structure, with each carbon atom in the chain carrying a methyl group. The presence of this methyl group gives the polypropylene molecular chain a certain rigidity and regularity. When reacting with a sulfonating agent, the reaction rate is moderate, which is more conducive to controllable nucleation and growth and makes it easier to obtain nanoscale small-diameter graphene. This allows for better coating of the cathode material and improves the conductivity of the cathode material.

[0024] The number-average molecular weight of the macromolecular organic material is preferably between 5,000 and 150,000, specifically 5,000, 8,000, 10,000, 20,000, 40,000, 60,000, 80,000, 100,000, 120,000, 140,000, 150,000, or any value between them. Furthermore, the small-molecule organic material and the high-molecular organic material may or may not be substituted with heteroatoms. The heteroatoms may be at least one of Cl, S, P, N, etc. Unsubstituted heteroatoms are preferred because the introduction of heteroatoms complicates the reaction and makes it difficult to control. Additionally, heteroatoms may enter the graphene lattice formed in the liquid-phase reaction, introducing more defects, disrupting the periodic structure of carbon atoms in the graphene microsheets, leading to a decrease in the conductivity of the final product. Furthermore, during subsequent lithium-ion battery charge-discharge tests, uncontrollable side reactions may occur at the graphene impurity sites, increasing the battery's internal resistance and affecting its cycle performance.

[0025] The present invention does not particularly limit the type of sulfonating agent, and can be any existing substance that can replace some hydrogen atoms in organic materials with sulfonic acid groups to achieve sulfonation. Examples include at least one of chlorosulfonic acid, concentrated sulfuric acid, fuming sulfuric acid, etc., with chlorosulfonic acid being preferred.

[0026] In this invention, in step S1, the pre-reaction temperature is 30–35°C, such as 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, or any value between them. When the pre-reaction temperature is below 30°C, the organic material cannot effectively dehydrogenate to form free monomers, which will affect subsequent nucleation and the synthesis of graphene in the liquid phase. When the pre-reaction temperature is above 35°C, the organic material undergoes dehydrogenation-condensation, and the nucleation and growth rate accelerates, rapidly fusing into a large-diameter carbon film. The sulfonated graphene formed therefrom will form a pomegranate shape when subsequently encapsulating the cathode material, failing to effectively encapsulate the cathode material particles. This prevents effective improvement of the cathode material's conductivity and affects the capacity of the lithium-ion battery. The pre-reaction time can be reasonably selected based on the reaction temperature, as long as it allows the organic material to achieve dehydrogenation condensation carbonization using the sulfonating agent as a catalyst and initially decompose into a disordered carbon film at the nanoscale. Specifically, the pre-reaction time is preferably 15 min to 40 min, such as 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min, or any value between them. The pre-reaction temperature and time can be any value within the above range, and will not be listed here.

[0027] In this invention, to ensure a more complete pre-reaction, the pre-reaction is preferably carried out under stirring conditions. The stirring rate is preferably 150–350 rpm, such as 150 rpm, 180 rpm, 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, 320 rpm, 350 rpm, or any value between them. The stirring rate can be any value within the above range, and will not be enumerated here.

[0028] In this invention, the pre-reaction product is first dispersed in water before undergoing a high-pressure hydrothermal reaction. The purpose of dispersing the pre-reaction product in water first is to halt the further fusion and growth reaction of the small-diameter carbon microplates formed at a lower temperature. The preferred mass ratio of the pre-reaction product to water is 1:(1-5), specifically 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or any value between them. The ratio of the pre-reaction product to water can be any value within the above range, and will not be enumerated here.

[0029] In this invention, the pre-reaction product can be dispersed in water by adding all of the pre-reaction product to the water at once and stirring until evenly dispersed, or by adding the pre-reaction product to the water in batches and stirring until evenly dispersed. A particularly preferred method is to slowly add the pre-reaction product dropwise to the water, and then continue stirring for 5–30 minutes (e.g., 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min, or any value between these). Using this preferred method avoids the pre-reaction product from agglomerating in the water, preventing it from being coiled or entangled. Instead, it allows the pre-reaction product to fully expand in the water, enabling it to undergo structural repair during the high-pressure hydrothermal reaction, transforming from a disordered to an ordered structure. Simultaneously, the final product, nanoscale carbon material flakes, retains its expanded state, facilitating good coating of the cathode material and ensuring full utilization of the carbon material. This imparts better conductivity and structural stability to the cathode material, thereby improving the rate performance and cycle performance of lithium-ion batteries. Furthermore, the rate at which the pre-reaction product is added to water is preferably 2 to 20 mL / min, such as 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 mL / min or any value between them.

[0030] In this invention, the temperature of the high-pressure hydrothermal reaction needs to be controlled between 160 and 220°C, specifically 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, or any value between them. When the high-pressure hydrothermal reaction temperature is below 160°C, the pre-reaction product carbon microplates cannot be effectively transformed from an amorphous carbon structure to a more crystalline carbon structure. Simultaneously, the sulfonate ions obtained from the dissociation of sulfuric acid cannot be firmly attached to the surface or edges of the carbon material, thus preventing the formation of water-soluble nanoscale sulfonated graphene. When the high-pressure hydrothermal reaction temperature exceeds 220℃, the dissociation of sulfuric acid molecules in the solution into sulfonate is hindered, leading to the dissociation into other products. This results in a low sulfonate concentration, hindering effective grafting onto graphene microsheets. Furthermore, at temperatures above 220℃, the sulfonate molecules suspended on the graphene microsheets may detach, causing poor water solubility in the final product. This prevents the product from achieving the "wetting and coating" effect on the substrate surface like a liquid solution, thus hindering uniform coating of the cathode material in the liquid phase. The pressure of the high-pressure hydrothermal reaction is preferably 1.5–2.5 MPa, specifically 1.5 MPa, 1.8 MPa, 2 MPa, 2.2 MPa, 2.5 MPa, or any value between them. The duration of the high-pressure hydrothermal reaction is preferably 4–8 hours, specifically 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or any value between them. The temperature, pressure, and time of the high-pressure hydrothermal reaction can be any value within the above range, and will not be enumerated here.

[0031] In this invention, in step S2, the preferred heating rate for raising the dispersion formed from the pre-reaction product and water to the high-pressure hydrothermal reaction temperature is 10–15 °C / min, specifically 10, 11, 12, 13, 14, or 15 °C / min or any value between them. This rate can impart better rate performance and cycle performance to the lithium-ion battery. The reason for this is likely that at this heating rate, the incompletely dehydrogenated organic materials remaining in the pre-reaction product are better able to react and transform into carbon material microflakes. Furthermore, this ensures that the nanoscale carbon material microflakes maintain their expanded morphology. Simultaneously, it ensures that the sulfuric acid in the solution gradually dissociates to form sulfonate ions, which are then selectively grafted onto the surface and edges of the graphene microflakes, avoiding any impact on the water solubility or conductivity of the final product. This allows the final product, after being coated with the cathode material, to exhibit better electrochemical performance when subsequently used in lithium-ion batteries.

[0032] In a preferred embodiment, the method for preparing sulfonated graphene further includes dispersing the product after a high-pressure hydrothermal reaction, centrifuging the dispersed product to remove residue, dialysis washing the supernatant, and spray drying the resulting retentate to obtain sulfonated graphene powder. Specifically, the dispersion treatment can be ultrasonic dispersion, mechanical stirring dispersion, or a combination of both. The dispersion treatment time is preferably 1–3 hours, specifically 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, or any value between them. In addition, the centrifugation speed is preferably 6000–8000 rpm, specifically 6000, 6200, 6400, 6600, 6800, 7000, 7200, 7400, 7600, 7800, or 8000 rpm; the centrifugation time is preferably 5–10 min, specifically 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min, or 10 min, or any value between them. Centrifugation is used to remove unreacted organic precursor materials and carbon material flakes that failed to form water-soluble flakes by precipitation. Furthermore, the particle size D50 of the sulfonated graphene powder is 20nm to 30nm, such as 20nm, 20.5nm, 21nm, 21.5nm, 22nm, 22.5nm, 23nm, 23.5nm, 24nm, 24.5nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm or any value between them; and the particle size D99 is 100nm to 110nm, such as 100nm, 102nm, 104nm, 106nm, 108nm, 110nm or any value between them.

[0033] The present invention also provides sulfonated graphene prepared by the above method.

[0034] This invention also provides the application of the above-mentioned sulfonated graphene as a carbon material coating agent for cathode materials.

[0035] The present invention also provides a modified cathode material, wherein the modified cathode material comprises a cathode material matrix and a coating layer covering the surface of the cathode material matrix, the coating layer being formed of the aforementioned sulfonated graphene. The improvement of the modified cathode material provided by the present invention lies in the use of a novel coating layer material, while the type of cathode material and the ratio between the cathode material and the coating layer can be conventional choices in the art, which are well known to those skilled in the art and will not be elaborated upon here.

[0036] The method for preparing the modified cathode material provided by the present invention includes dispersing the above-mentioned sulfonated graphene in water, then mixing the obtained sulfonated graphene dispersion with the cathode material and / or cathode material precursor evenly, and then filtering, drying and calcining the obtained mixture in sequence to obtain the modified cathode material.

[0037] In the preparation process of the above modified cathode material, the preferred ratio of sulfonated graphene to water is (100-140) g:1L, such as 100 g:1L, 110 g:1L, 120 g:1L, 130 g:1L, 140 g:1L or any value between them.

[0038] In the preparation process of the modified cathode material, the mass ratio of the amount of sulfonated graphene to the amount of cathode material and / or cathode material precursor is preferably (1-2):100, such as 1.0:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100, 2.0:100 or any value between them.

[0039] In the preparation process of the modified cathode material, the drying conditions preferably include a temperature of 80-120°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or any value between them; and a time of 5-8h, such as 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h or any value between them.

[0040] In the preparation process of the above-mentioned modified cathode material, the calcination conditions preferably include a temperature of 600-650℃, such as 600℃, 605℃, 610℃, 615℃, 620℃, 625℃, 630℃, 635℃, 640℃, 645℃, 650℃ or any value between them; and a time of 6-8h, such as 6h, 6.2h, 6.5h, 6.8h, 7h, 7.2h, 7.4h, 7.6h, 7.8h, 8h or any value between them.

[0041] The present invention will be described in detail below through embodiments.

[0042] Preparation Example 1

[0043] S1. Fix the three-necked flask in a water bath, and add 1000 mL of chlorosulfonic acid and polypropylene (purchased from Suzhou Qihuida Engineering Plastics Co., Ltd., brand name T30S, number average molecular weight of 20000) to the three-necked flask in sequence. The mass ratio of polypropylene to chlorosulfonic acid is 1:10. Heat the water bath to 30°C and stir the mixture at 200 rpm for 40 min to obtain the pre-reaction product.

[0044] S2. The pre-reaction product was slowly added dropwise to pure water and stirred at 200 rpm. The mass ratio of the pre-reaction product to pure water was 1:1, and the dropping rate was controlled at 2 mL / min. After the addition was complete, stirring was continued for 15 min to obtain a dispersion. The dispersion was transferred to a polytetrafluoroethylene-lined reactor and heated to 160°C at a rate of 10°C / min. The reaction was carried out at 160°C and 1.5 MPa for 8 h. The resulting reaction product was ultrasonically dispersed (power 60 kHz) with mechanical stirring (stirring speed 200 rpm) for 2 h. The dispersion was then centrifuged at 6000 rpm for 10 min. The supernatant after centrifugation was dialyzed until the pH value was close to neutral. The resulting retentate was spray-dried at an inlet temperature controlled at 220°C and a feed rate controlled at 0.7 L / h to obtain sulfonated graphene powder, denoted as HM-1.

[0045] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 98.1%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0046] Laser particle size analyzer measurements showed that the particle size (D50) of the sulfonated graphene powder was 20 nm, and the D99 was 100 nm. The Raman spectroscopy results of the sulfonated graphene powder are shown below. Figure 1 , Figure 1 The 2D peak characteristic signal of graphene can be clearly seen. Although some defects are seen in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment is significantly repaired compared to the disordered structure of activated carbon.

[0047] SEM image of the sulfonated graphene powder is as follows: Figure 2 As shown, from Figure 2 As can be seen, a large number of regular spheres are formed after spray drying. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale micro-flakes are difficult to observe under an electron microscope, this method can indirectly illustrate that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0048] Elemental analysis using EDS yielded a C:S ratio of 7.72:1. The infrared spectrum of this sulfonated graphene powder is shown below. Figure 3 As shown, from Figure 3 It can be seen that at a wavenumber of 1178 cm⁻¹ -1 1060cm -1Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 33 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0049] Preparation Example 2

[0050] S1. Fix the three-necked flask in a water bath, and add 1000 mL of chlorosulfonic acid and polypropylene (purchased from Suzhou Qihuida Engineering Plastics Co., Ltd., grade T20, number average molecular weight of 15000) to the three-necked flask in sequence. The mass ratio of polypropylene to chlorosulfonic acid is 1:15. Heat the water bath to 35°C and stir the mixture at 350 rpm for 15 min to obtain the pre-reaction product.

[0051] S2. The pre-reaction product was slowly added dropwise to pure water and stirred at 200 rpm. The mass ratio of the pre-reaction product to pure water was 1:1.5, and the dropping rate was controlled at 5 mL / min. After the addition was complete, stirring was continued for 25 min to obtain a dispersion. The dispersion was transferred to a polytetrafluoroethylene-lined reactor and heated to 220°C at a rate of 15°C / min. The reaction was carried out at 220°C and 2.5 MPa for 4 h. The resulting reaction product was ultrasonically dispersed (power 40 kHz) with mechanical stirring (stirring speed 200 rpm) for 3 h. The dispersion was then centrifuged at 7000 rpm for 8 min and filtered. The supernatant after centrifugation was dialyzed until the pH value was close to neutral. The resulting retentate was spray-dried at an inlet temperature controlled at 200°C and a feed rate controlled at 0.5 L / h to obtain sulfonated graphene powder, denoted as HM-2.

[0052] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 98.5%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0053] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0054] Laser particle size analyzer measurements showed that the D50 of the sulfonated graphene powder was 22.5 nm, and the D99 was 103.1 nm. Raman spectroscopy clearly revealed the 2D characteristic signals of graphene. Although numerous defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.81:1. Infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.5 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0055] Preparation Example 3

[0056] S1. Fix the three-necked flask in a water bath, and add 1000 mL of chlorosulfonic acid and polypropylene (purchased from Nanjing Tianshi New Material Technology Co., Ltd., brand name PPW-0910, number average molecular weight of 40000) to the three-necked flask in sequence. The mass ratio of polypropylene to chlorosulfonic acid is 1:20. Heat the water bath to 32°C and stir the mixture at 150 rpm for 25 min to obtain the pre-reaction product.

[0057] S2. The pre-reaction product was slowly added dropwise to pure water and stirred at 200 rpm. The mass ratio of the pre-reaction product to pure water was 1:5, and the dropping rate was controlled at 20 mL / min. After the addition was complete, stirring was continued for 20 min to obtain a dispersion. The dispersion was transferred to a polytetrafluoroethylene-lined reactor and heated to 200 °C at a rate of 13 °C / min. The reaction was carried out at 200 °C and 2.35 MPa for 6 h. The resulting reaction product was ultrasonically dispersed (power 80 kHz) with mechanical stirring (stirring speed 200 rpm) for 1 h. The dispersion was then centrifuged at 8000 rpm for 5 min. The supernatant after centrifugation was dialyzed until the pH value was close to neutral. The resulting retentate was spray-dried at an inlet temperature controlled at 210 °C and a feed rate controlled at 0.6 L / h to obtain sulfonated graphene powder, denoted as HM-3.

[0058] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 97.8%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0059] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0060] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 20.5 nm and a D99 of 102.3 nm. Raman spectroscopy revealed clear 2D characteristic signals of graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.79:1. Infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹ showed... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured by a powder resistivity tester, was 34.1 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0061] Preparation Example 4

[0062] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that polypropylene was replaced with polyethylene (purchased from Nanjing Tianshi New Material Technology Co., Ltd., brand name PEW-0320, number average molecular weight of 20000) of the same weight and molecular weight. The other conditions were the same as in Preparation Example 1, and sulfonated graphene powder was obtained, denoted as HM-4.

[0063] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polyethylene is recorded as m2. The precursor polyethylene conversion rate in this embodiment is calculated as (m2-m1) / m2*100%, which is 98.3%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polyethylene and the nucleation-growth of graphene to be more complete, and they are basically converted into water-soluble sulfonated graphene.

[0064] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0065] Laser particle size analyzer measurements showed that the particle size D50 of the sulfonated graphene powder was 22.7 nm, and the D99 was 103.4 nm. Raman spectroscopy revealed a clear 2D peak characteristic signal for graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.78:1. Furthermore, infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹ showed... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.3 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0066] Preparation Example 5

[0067] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that polypropylene was replaced with polystyrene of the same weight and molecular weight (purchased from Yangzi Petrochemical-BASF Co., Ltd., grade 143E, number average molecular weight 35,000), and the other conditions were the same as in Preparation Example 1, resulting in sulfonated graphene powder, denoted as HM-5.

[0068] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polystyrene is recorded as m2. The conversion rate of the precursor polystyrene in this embodiment is calculated as (m2-m1) / m2*100%, which is 98.1%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polystyrene and the nucleation and growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0069] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0070] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 20.3 nm and a D99 of 101.2 nm. Raman spectroscopy clearly revealed the 2D characteristic signal of graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed that C:S = 7.75:1; furthermore, infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹ showed... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 33.6 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0071] Preparation Example 6

[0072] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that in step S2, the pre-reaction product was added to water all at once, while the other conditions were the same as in Preparation Example 1. The specific steps are as follows:

[0073] S1. Fix the three-necked flask in a water bath, and add 1000 mL of chlorosulfonic acid and polypropylene (purchased from Suzhou Qihuida Engineering Plastics Co., Ltd., brand name T30S, number average molecular weight of 20000) to the three-necked flask in sequence. The mass ratio of polypropylene to chlorosulfonic acid is 1:10. Heat the water bath to 30°C and stir the mixture at 200 rpm for 40 min to obtain the pre-reaction product.

[0074] S2. The pre-reaction product was added to pure water in one go while stirring at 200 rpm, with a mass ratio of 1:1 between the pre-reaction product and pure water. After the addition was complete, stirring was continued at 200 rpm for 15 min to obtain a dispersion. The dispersion was transferred to a polytetrafluoroethylene-lined reactor and heated to 160°C at a rate of 10°C / min. The reaction was carried out at 160°C and 1.5 MPa for 8 h. The resulting reaction product was then dispersed by ultrasonication (60 kHz) with mechanical stirring (200 rpm) for 2 h. The dispersion was then centrifuged at 6000 rpm for 10 min. The supernatant after centrifugation was dialyzed until the pH value was close to neutral. The resulting retentate was spray-dried at an inlet temperature of 220°C and a feed rate of 0.7 L / h to obtain sulfonated graphene powder, denoted as HM-6.

[0075] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 97.7%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0076] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0077] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 21.4 nm and a D99 of 103.1 nm. Raman spectroscopy clearly revealed the 2D characteristic signals of graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.85:1. Infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 33.8 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0078] Preparation Example 7

[0079] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that the heating rate of the dispersion formed by the pre-reaction product and water to the high-pressure hydrothermal reaction temperature was controlled at 7°C / min (i.e., not within the preferred range of the present invention), and the other conditions were the same as in Preparation Example 1, and sulfonated graphene powder was obtained, denoted as HM-7.

[0080] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 97.6%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0081] As shown in the SEM image, the sulfonated graphene powder obtained after spray drying is spherical. According to the general characteristics of nanomaterials, droplets formed by spraying a mixture of small-sized nanoparticles will form spherical particles after rapid drying. In addition, since nanoscale microflakes are difficult to observe under an electron microscope, this indirectly demonstrates that the sulfonated graphene powder obtained by the method of this embodiment has a small size.

[0082] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 20.7 nm and a D99 of 101.5 nm. Raman spectroscopy revealed clear 2D characteristic signals of graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.8:1. Infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.0 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0083] Comparative Preparation Example 1

[0084] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that the pre-reaction temperature in step S1 was controlled at 40°C, and the other conditions were the same as in Preparation Example 1, resulting in sulfonated graphene powder, denoted as DHM-1.

[0085] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 98.3%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material polypropylene and the nucleation-growth of graphene to be more complete, and basically convert them into water-soluble sulfonated graphene.

[0086] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 30 μm and a D99 of 75 μm, indicating a relatively large flake size. This is likely due to the excessively high pre-reaction temperature, resulting in a rapid nucleation and growth rate, causing the carbon microflakes formed by the dehydrogenation and condensation of the precursor to quickly fuse into a large-scale carbon film. Raman spectroscopy clearly revealed the 2D characteristic signal of graphene. Although some defects were observed in the Raman spectrum, the lattice structure of the sulfonated graphene prepared in this embodiment was significantly repaired compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.96:1. Infrared spectroscopy measurements at a wavenumber of 1178 cm⁻¹ showed... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.7 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0087] Comparative Preparation Example 2

[0088] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that the pre-reaction in step S1 was carried out in water, and water was not added in step S2. The specific steps are as follows:

[0089] S1. Fix the three-necked flask in a water bath, and add 1000 mL of chlorosulfonic acid, polypropylene, and water to the three-necked flask in sequence. The mass ratio of polypropylene to chlorosulfonic acid is 1:10, and the total amount of polypropylene and chlorosulfonic acid is in the mass ratio of pure water to 1:1. Heat the water bath to 30°C and stir the mixture at 200 rpm for 40 min to obtain the pre-reaction product.

[0090] S2. The pre-reaction product was transferred to a polytetrafluoroethylene-lined reactor and heated to 160°C at a rate of 10°C / min. The reaction was carried out at 160°C and 1.5MPa for 8 hours. The resulting reaction product was then dispersed by ultrasonication (60KHz) with mechanical stirring (200rpm) for 2 hours. The dispersed product was then centrifuged at 6000rpm for 10 minutes. The supernatant after centrifugation was dialyzed until the pH value was close to neutral. The resulting retentate was spray-dried at an inlet temperature of 220°C and a feed rate of 0.7L / h to obtain the target product, denoted as DHM-2.

[0091] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1. The mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, resulting in a precursor conversion rate of 15%. This indicates that the method provided in this embodiment inhibits the dehydrogenation polymerization of the precursor polypropylene and the nucleation and growth of graphene in the liquid phase, thus affecting the synthesis of nanoscale graphene flakes and causing a significant decrease in the precursor conversion rate. Laser particle size analysis shows that the particle size D50 of the sulfonated graphene powder is 23 nm, and the D99 is 104 nm. Raman spectroscopy analysis shows... Figure 4 As shown, 2D characteristic signals of graphene can be observed, but the number of defects is significantly increased. This may be because the pre-reaction stage is carried out in an aqueous medium, which not only results in a slow reaction but also random condensation and carbonization, leading to poor nucleation and numerous defects in the final product. EDS elemental analysis shows that C:S = 8.05:1. Infrared spectroscopy at a wavenumber of 1178 cm⁻¹... -1 1060cm -1 Characteristic peaks were observed in the vicinity, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment was 55.4 mΩ·cm, indicating decreased conductivity, which may be related to the increase in defects.

[0092] Comparative preparation example 3

[0093] Sulfonated graphene was prepared according to the method of Preparation Example 1, except that the water in step S2 was replaced with the same amount of hexadecane by weight, and the other conditions were the same as in Preparation Example 1, resulting in sulfonated graphene powder, denoted as DHM-3.

[0094] According to laser particle size analyzer tests, the particle size D50 of the sulfonated graphene powder is 37 μm and the D99 is 82 μm, with a significant increase in flake size. This may be because hexadecane provides a carbon source to participate in the reaction during the high-pressure hydrothermal reaction, which causes the carbon microflakes formed in the pre-reaction to undergo structural repair during the high-pressure hydrothermal reaction, while the flake size also increases further.

[0095] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor polypropylene is recorded as m2. The conversion rate of the precursor polypropylene in this embodiment is calculated as (m2-m1) / m2*100%, which is 101.8%. This further illustrates that the method provided in this embodiment uses hexadecane as a carbon source to participate in the reaction.

[0096] Raman spectroscopy clearly revealed characteristic graphene signals. Although some defects were observed in the Raman spectrum, the sulfonated graphene lattice structure prepared in this embodiment showed significant repair compared to the disordered structure of activated carbon. EDS elemental analysis showed a C:S ratio of 7.98:1. Infrared spectroscopy at a wavenumber of 1178 cm⁻¹... -1 1060cm -1 Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.0 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0097] Comparative preparation example 4

[0098] In a fume hood, 600g of 99% pure chlorosulfonic acid was added to an open 2L three-necked glass reactor as the reaction medium. The reactor was heated to 50°C using an oil bath and maintained at that temperature. 10g of hexadecane was added, and the reaction was carried out for 3 hours. Then, the temperature was slowly increased to 160°C and the reaction was maintained at that temperature for 12 hours. The reaction was cooled, and the contents of the reactor were centrifuged at 6000 rpm for 10 minutes. The supernatant after centrifugation was dialyzed and dried to obtain sulfonated graphene, denoted as DHM-4.

[0099] The mass of the precipitate after centrifugation of the dispersion product, after washing and drying, is recorded as m1, and the mass of the precursor hexadecane is recorded as m2. The conversion rate of the precursor hexadecane in this embodiment is calculated as (m2-m1) / m2*100%, which is 97.1%. This indicates that the method provided in this embodiment can enable the catalytic dehydrogenation polycondensation of the precursor organic material hexadecane and the nucleation-growth of graphene to be more complete, and they are basically converted into water-soluble sulfonated graphene.

[0100] Laser particle size analyzer measurements showed that the sulfonated graphene powder had a D50 of 47 μm and a D99 of 95 μm, indicating a significantly larger flake size. This is likely due to the vigorous reaction of hexadecane in the chlorosulfonic acid medium, coupled with a high pre-reaction temperature, resulting in rapid nucleation and growth, leading to the formation of larger carbon micro-flakes. Subsequent high-pressure hydrothermal reaction further resulted in a significantly larger final product flake size. Raman spectroscopy clearly revealed the characteristic graphene signal. EDS elemental analysis showed a C:S ratio of 7.76:1. Infrared spectroscopy at a wavenumber of 1178 cm⁻¹... -1 1060cm -1Characteristic peaks were observed in the vicinity of the graphene, corresponding to the -SO3H group, indicating that sulfonic acid groups have been successfully bonded to the graphene. The resistivity of the sulfonated graphene powder prepared in this embodiment, measured using a powder resistivity tester, was 34.5 mΩ·cm, indicating that the sulfonated graphene prepared in this embodiment has good electrical conductivity.

[0101] Example 1

[0102] 20g of sulfonated graphene powder HM-1 obtained from Preparation Example 1 was dispersed in 200mL of water. The resulting sulfonated graphene dispersion was then mixed evenly with lithium iron phosphate cathode material at a mass ratio of 1:100. The resulting mixture was then filtered and dried at 80°C for 8h. The dried product was then calcined at 650°C under nitrogen protection at a flow rate of 5L / min for 5h to obtain the modified cathode material.

[0103] Example 2

[0104] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the same weight of sulfonated graphene powder HM-2 obtained from Preparation Example 2. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0105] Example 3

[0106] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the same weight of sulfonated graphene powder HM-3 obtained from Preparation Example 3. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0107] Example 4

[0108] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the same weight of sulfonated graphene powder HM-4 obtained from Preparation Example 4. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0109] Example 5

[0110] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the sulfonated graphene powder HM-5 obtained from Preparation Example 5 in the same weight proportions. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0111] Example 6

[0112] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the same weight of sulfonated graphene powder HM-6 obtained from Preparation Example 6. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0113] Example 7

[0114] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the same weight of sulfonated graphene powder HM-7 obtained from Preparation Example 7. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0115] Comparative Example 1

[0116] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the sulfonated graphene powder DHM-1 obtained from Comparative Preparation Example 1 in the same weight proportions. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0117] Comparative Example 2

[0118] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the sulfonated graphene powder DHM-2 obtained from Comparative Preparation Example 2 with the same weight parts. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0119] Comparative Example 3

[0120] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the sulfonated graphene powder DHM-3 obtained from Comparative Preparation Example 3 in the same weight proportions. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0121] Comparative Example 4

[0122] The modified cathode material was prepared according to the method of Example 1, except that the sulfonated graphene powder HM-1 obtained from Preparation Example 1 was replaced by the sulfonated graphene powder DHM-4 obtained from Comparative Preparation Example 4 in the same weight proportions. The other conditions were the same as in Example 1, and the modified cathode material was obtained.

[0123] Test case

[0124] The modified cathode materials obtained in the above embodiments and comparative examples were mixed with conductive carbon black Super P and binder PVDF in NMP at a weight ratio of 92:3:5, and then coated onto aluminum foil to obtain electrode sheets. The electrode sheets were dried in an 80°C forced-air oven and then placed in a 120°C vacuum oven for overnight drying. The dried electrode sheets were then rolled and pressed to serve as the battery cathode (compacted density of 2.3 g / cm³). 3 Lithium metal was used as the negative electrode, Celgard 2400 was used as the separator, and 1M LiPF6-EC-DMC-EMC (i.e., the concentration of LiPF6 in EC-DMC-EMC solvent is 1M, where EC is ethylene carbonate, DMC is dimethyl carbonate, EMC is methyl ethyl carbonate, and the volume ratio of EC:DMC:EMC is 1:1:1) was used as the electrolyte. The 2032 battery was assembled and electrochemical tests were conducted.

[0125] (1) Discharge specific capacity: After the above 2032 batteries were placed at 25°C for 6 hours, they were charged at a constant current of 0.1C to the cutoff voltage of 3.85V, then charged at a constant voltage to the cutoff current of 0.02C, and then discharged at a constant current of 7C to the cutoff voltage of 2.0V. The discharge specific capacity of the positive electrode material was obtained by dividing this discharge capacity by the mass of the active material (i.e., the modified positive electrode material). The results are shown in Table 1.

[0126] (2) Cycling performance: The CR2032 batteries were charged and discharged 100 times at room temperature with a current density of 7C in a voltage range of 2 to 3.85V. The discharge specific capacity was then tested again, and the capacity retention rate was calculated based on the discharge specific capacity after 100 cycles / the initial discharge specific capacity. The results are shown in Table 1.

[0127] (3) Battery impedance: The electrochemical impedance of the assembled coin cells was tested using an electrochemical workstation with a scanning frequency of 0.1 Hz to 1 MHz and a voltage amplitude of ±10 mV. The results are shown in Table 1.

[0128] Table 1

[0129]

[0130] The results from Examples 1 to 7 show that when sulfonated graphene obtained by the method provided by the present invention is used to coat the cathode material, the rate performance and cycle performance of lithium-ion batteries can be significantly improved.

[0131] A comparison of Examples 1 and 6 shows that in step S2, when the pre-reaction product is dispersed in water by slowly adding the pre-reaction product dropwise into the water and then continuing to stir and react for a period of time after the addition is complete, it is more beneficial to improve the rate performance and cycle performance of lithium-ion batteries.

[0132] A comparison of Examples 1 and 7 shows that when the heating rate of the dispersion formed by the pre-reaction product and water to the high-pressure hydrothermal reaction temperature is controlled within a preferred range, the lithium-ion battery can be given better rate performance and cycle performance.

[0133] As can be seen from the comparison between Example 1 and Comparative Example 1, exceeding the range of this application for the pre-reaction temperature will affect the capacity of the lithium-ion battery.

[0134] The comparison between Example 1 and Comparative Example 2 shows that when the water is added in advance to the pre-reaction step, the rate performance and cycle performance of the lithium-ion battery will decrease.

[0135] The comparison between Example 1 and Comparative Example 3 shows that when the high-pressure hydrothermal reaction is carried out in a non-aqueous solution, the rate performance and cycle performance of the lithium-ion battery are poor.

[0136] The comparison between Example 1 and Comparative Example 4 shows that conventional methods for preparing sulfonated graphene cannot effectively improve the rate performance and cycle performance of lithium-ion batteries.

[0137] 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 without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing sulfonated graphene, characterized in that, The method includes the following steps: S1. An organic material and a sulfonating agent are pre-reacted at 30-35°C in the absence of a reactive medium to obtain a pre-reaction product; wherein the organic material is selected from at least one of polyethylene, polypropylene, polyimide and polystyrene; S2. The pre-reaction product is slowly added dropwise to water at a rate of 2-20 mL / min. After the addition is complete, stirring is continued for 5-30 min. The resulting dispersion is then heated to 160-220 °C for high-pressure hydrothermal reaction to obtain sulfonated graphene.

2. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S1, the mass ratio of the organic material to the sulfonating agent is 1:(10~20).

3. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S1, the sulfonating agent is selected from at least one of chlorosulfonic acid, concentrated sulfuric acid, and fuming sulfuric acid.

4. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S1, the pre-reaction time is 15 min to 40 min.

5. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S2, the mass ratio of the pre-reaction product to water is 1:(1~5).

6. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S2, the rate at which the dispersion is heated to the high-pressure hydrothermal reaction temperature is 10~15℃ / min.

7. The method for preparing sulfonated graphene according to claim 1, characterized in that, In step S2, the high-pressure hydrothermal reaction takes 4 to 8 hours.

8. The method for preparing sulfonated graphene according to claim 1, characterized in that, The method also includes dispersing the product after high-pressure hydrothermal reaction, centrifuging the dispersed product to remove residue, dialysis and washing the filtrate, and spray drying the retentate to obtain sulfonated graphene powder.

9. The method for preparing sulfonated graphene according to claim 8, characterized in that, The dispersion process is performed by ultrasonic dispersion and / or mechanical stirring dispersion.

10. The method for preparing sulfonated graphene according to claim 8, characterized in that, The dispersion processing time is 1 to 3 hours.

11. The method for preparing sulfonated graphene according to claim 8, characterized in that, The sulfonated graphene powder has a particle size D50 of 20nm~30nm and a particle size D99 of 100nm~110nm.

12. Sulfonated graphene prepared by the method according to any one of claims 1 to 11.

13. The application of sulfonated graphene as described in claim 12 as a carbon material coating agent for cathode materials.

14. A modified cathode material, characterized in that, The modified cathode material includes a cathode material matrix and a coating layer covering the surface of the cathode material matrix, wherein the coating layer is formed from the sulfonated graphene of claim 12.

15. A method for preparing the modified cathode material according to claim 14, the method comprising dispersing the sulfonated graphene according to claim 12 in water, then mixing the obtained sulfonated graphene dispersion with the cathode material and / or the cathode material precursor evenly, and then sequentially filtering, drying and calcining the obtained mixture to obtain the modified cathode material.

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