Carboxyl-modified graphite, method for producing the same, and lithium ion battery using the same

Abstract

This invention relates to a carboxyl-modified graphite, its preparation method, and a lithium-ion battery using this material. The graphite preparation method includes steps for preparing porous graphite oxide and preparing carboxyl-modified graphite. The graphite surface contains numerous nanoscale pores, larger interlayer spacing than virgin graphite, and a small number of oxygen functional groups such as carboxyl groups, exhibiting rapid solubility. When used in lithium-ion batteries, it significantly improves the wettability of the negative electrode material with the electrolyte while maintaining the stability of the graphite structure, thereby increasing the lithium-ion insertion / extraction rate and optimizing the battery's rate performance. Simultaneously, the small number of carboxyl functional groups improves graphite dispersion and increases the interlayer spacing, further enhancing lithium-ion transport kinetics.

Description

Technical Field

[0001] This invention relates to the field of new energy batteries, and in particular to a carboxyl-modified graphite, its preparation method, and a lithium-ion battery using the material. Background Technology

[0002] The widespread application of electric vehicles and renewable energy technologies requires high-energy-density and low-cost batteries, with lithium-ion batteries currently leading the technology. In commercial applications, carbon anode materials (including artificial and natural graphite) account for over 95% of lithium-ion battery anode materials. Currently, developing novel high-performance, low-cost anode materials to replace graphite still faces many technical challenges; therefore, graphite anodes will continue to be the mainstream choice for lithium-ion batteries in the foreseeable future.

[0003] However, due to graphite's small interlayer spacing (approximately 0.335 nm) and small specific surface area (1.7-13.8 m²), it has limited advantages in many applications. 2 The graphite's poor conductivity (in g) results in a slow lithium-ion insertion / extraction rate, which is increasingly unable to meet the development requirements of high-power lithium-ion batteries. Furthermore, during high-rate charge / discharge, the expansion and contraction of the graphite structure can easily lead to detachment from the current collector, reducing battery life. Moreover, because graphite does not contain any polar groups, its dispersibility is poor. Therefore, water-soluble dispersants are needed to assist dispersion when preparing the negative electrode slurry. Even so, prolonged high-speed stirring is still required, and balancing the stirring time with the amount of materials is difficult. For example, too short a stirring time makes it difficult to ensure uniform dispersion of graphite, conductive agents, and binders, while too long a stirring time may increase the viscosity of the slurry, affecting coating performance. It is worth noting that since the dispersant itself is non-conductive, its introduction increases the internal resistance of the electrode, thereby reducing the battery's charge / discharge efficiency.

[0004] To address the inherent defects of graphite as a negative electrode in lithium-ion batteries, researchers have developed numerous methods to modify graphite, such as spheroidization, surface modification, and doping. Patent CN110600715A proposes a method to improve the sphericity of graphite by refining its particle size, thereby shortening the lithium-ion migration path. Further, it involves heat-treating the graphite at 2800–3000℃ and 1000–1300℃ under nitrogen or argon atmospheres to form a carbon-coated structure, improving the current performance of the negative electrode material. However, this high-temperature sintering process undoubtedly increases industrialization costs, and modified graphite still cannot avoid the problem of poor processing performance due to poor dispersibility.

[0005] Patent CN113511651A discloses a method for preparing anode materials using polypyrrole-modified micro-oxidized expanded graphite. This method involves modifying graphite with numerous oxygen functional groups through a strong acid oxidation process, thereby enhancing its dispersibility and increasing the interlayer spacing, thus improving the lithium-ion insertion / extraction rate. The battery performance is further optimized by introducing the conductive polymer polypyrrole. While increasing the graphite interlayer spacing can improve the lithium-ion diffusion rate and induce a stronger and more stable solid electrolyte interphase (SEI) layer on the graphite surface, theoretical studies have also shown that the presence of oxygen-containing functional groups leads to poor electrode conductivity and significant irreversible capacity loss, causing the electrode capacity to rapidly decay within a few to several hundred cycles, thus shortening battery life.

[0006] In summary, the poor dispersibility, slow lithium-ion insertion / extraction rate, and incompatibility of processing technology with traditional slurry electrode processing of graphite as a negative electrode material for lithium-ion batteries remain problems that urgently need to be solved for the commercial application of carbon negative electrode materials for lithium-ion batteries. Summary of the Invention

[0007] In view of the above problems, this application provides a carboxyl-modified graphite, a preparation method, and a lithium-ion battery using this material. The carboxyl-modified graphite prepared by the method of this application has a large number of nanoscale pores on its surface, a larger interlayer spacing than original graphite, and a small number of oxygen functional groups such as carboxyl groups, exhibiting rapid solubility. This allows the anode material to significantly improve its wettability with the electrolyte while maintaining the stability of the graphite structure, thereby increasing the lithium-ion insertion / extraction rate and optimizing the battery's rate performance. Simultaneously, the small number of carboxyl functional groups improves graphite dispersion and increases the interlayer spacing, further enhancing the lithium-ion transport kinetics.

[0008] The first aspect of this application provides a method for preparing carboxyl-modified graphite, comprising the following steps: preparation of porous graphite oxide: adding water to graphite oxide and stirring to obtain a first dispersion; mixing the first dispersion with hydrogen peroxide and reacting hydrothermally at 160-180°C for 3-6 hours to obtain a hydrothermal product; separating the hydrothermal product into solid and liquid phases to obtain a first solid; washing the first solid to obtain porous graphite oxide; preparation of carboxyl-modified graphite: adding water to the porous graphite oxide and stirring to obtain a second dispersion; sequentially adding 95% sodium hydroxide and 98% chloroacetic acid to the second dispersion and reacting in a water bath for more than 3 hours to obtain a water bath product; separating the water bath product into solid and liquid phases to obtain a second solid; washing the second solid to obtain the carboxyl-modified graphite.

[0009] Unlike existing technologies, the carboxyl-modified graphite prepared by the method in this application contains numerous nanoscale pores on its surface, larger interlayer spacing than original graphite, and a small number of oxygen functional groups such as carboxyl groups, exhibiting rapid solubility. This allows the anode material to significantly improve its wettability with the electrolyte while maintaining the stability of the graphite structure, thereby increasing the lithium-ion insertion / extraction rate and optimizing the battery's rate performance. Simultaneously, the small number of carboxyl functional groups improves graphite dispersion and increases the interlayer spacing, further enhancing lithium-ion transport kinetics.

[0010] Furthermore, the preparation of the graphite oxide includes the following steps: adding flake graphite to a first mixed solution, stirring slowly until completely dispersed, and continuing to stir for 3-6 hours to obtain a third dispersion; performing solid-liquid separation and washing on the third dispersion to obtain graphite oxide; the first mixed solution is a mixed solution of 98% sulfuric acid, 98% nitric acid and sodium chlorate.

[0011] Furthermore, the mesh size of the flake graphite is 500-2000 mesh.

[0012] Furthermore, in the step of preparing graphite oxide, the mass ratio of 98% sulfuric acid, 98% nitric acid and sodium chlorate in the first mixed solution is 6:2:1.

[0013] Furthermore, in the porous graphite oxide preparation step, the hydrogen peroxide is a hydrogen peroxide solution with a volume percentage of 30-35%.

[0014] Furthermore, in the carboxyl-modified graphite preparation step, the mass ratio of porous graphite oxide, 95% sodium hydroxide, and 98% chloroacetic acid is 10:13:10.

[0015] Furthermore, in the carboxyl-modified graphite preparation step, the second solid is washed multiple times with distilled water until the pH of the washing solution is 6.9–7.1.

[0016] A second aspect of this application provides a carboxyl-modified graphite, characterized in that the carboxyl-modified graphite is prepared using the preparation method described in any one of claims 1-7.

[0017] Furthermore, the carboxyl-modified graphite is densely covered with pores ranging from 30 nm to 2 μm in size, and its interlayer spacing is 0.4-0.42 nm.

[0018] The third aspect of this application provides a lithium-ion battery, wherein the lithium-ion battery uses the carboxyl-modified graphite described in the second aspect of this application as the negative electrode material.

[0019] Unlike existing technologies, the carboxyl-modified graphite prepared by the method of this application is used as the negative electrode material. The lithium-ion battery was tested at 0.1C rate and 1C rate. The capacity at 1C rate was 2.6 times higher than that of untreated raw graphite. Moreover, at 1C rate, the capacity retention rate was significantly better than that of raw graphite after 100 cycles.

[0020] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the textual description, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and accompanying drawings of this application. Attached Figure Description

[0021] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0022] In the accompanying drawings of the instruction manual:

[0023] Figure 1 Scanning electron microscope image of carboxyl porous graphite particles with surface nanopore structure;

[0024] Figure 2 This study describes the method for testing settling time and the settling time of different example graphite products in aqueous environments.

[0025] Figure 3 These are photographs of graphite products from different embodiments after being left to stand in an aqueous environment for 20 minutes. Detailed Implementation

[0026] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0027] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0028] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0029] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0030] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0031] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0032] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0033] The first aspect of this application provides a method for preparing carboxyl-modified graphite, comprising the following steps: preparation of porous graphite oxide: adding water to graphite oxide and stirring to obtain a first dispersion; mixing the first dispersion with hydrogen peroxide and reacting hydrothermally at 160-180°C for 3-6 hours to obtain a hydrothermal product; separating the hydrothermal product into solid and liquid phases to obtain a first solid; washing the first solid to obtain porous graphite oxide; preparation of carboxyl-modified graphite: adding water to the porous graphite oxide and stirring to obtain a second dispersion; sequentially adding 95% sodium hydroxide and 98% chloroacetic acid to the second dispersion and reacting in a water bath for more than 3 hours to obtain a water bath product; separating the water bath product into solid and liquid phases to obtain a second solid; washing the second solid to obtain the carboxyl-modified graphite.

[0034] Unlike existing technologies, the carboxyl-modified graphite prepared by the method in this application contains numerous nanoscale pores on its surface, larger interlayer spacing than original graphite, and a small number of oxygen functional groups such as carboxyl groups, exhibiting rapid solubility. This allows the anode material to significantly improve its wettability with the electrolyte while maintaining the stability of the graphite structure, thereby increasing the lithium-ion insertion / extraction rate and optimizing the battery's rate performance. Simultaneously, the small number of carboxyl functional groups improves graphite dispersion and increases the interlayer spacing, further enhancing lithium-ion transport kinetics.

[0035] Furthermore, the preparation of the graphite oxide includes the following steps: adding flake graphite to a first mixed solution, stirring slowly until completely dispersed, and continuing to stir for 3-6 hours to obtain a third dispersion; performing solid-liquid separation and washing on the third dispersion to obtain graphite oxide; the first mixed solution is a mixed solution of 98% sulfuric acid, 98% nitric acid and sodium chlorate.

[0036] Furthermore, the mesh size of the flake graphite is 500-2000 mesh.

[0037] Furthermore, in the step of preparing graphite oxide, the mass ratio of 98% sulfuric acid, 98% nitric acid and sodium chlorate in the first mixed solution is 6:2:1.

[0038] Furthermore, in the porous graphite oxide preparation step, the hydrogen peroxide is a hydrogen peroxide solution with a volume percentage of 30-35%.

[0039] Furthermore, in the carboxyl-modified graphite preparation step, the mass ratio of porous graphite oxide, 95% sodium hydroxide, and 98% chloroacetic acid is 10:13:10.

[0040] Furthermore, in the carboxyl-modified graphite preparation step, the second solid is washed multiple times with distilled water until the pH of the washing solution is 6.9–7.1.

[0041] A second aspect of this application provides a carboxyl-modified graphite, characterized in that the carboxyl-modified graphite is prepared using the preparation method described in any one of claims 1-7.

[0042] Furthermore, the carboxyl-modified graphite is densely covered with pores ranging from 30 nm to 2 μm in size, and its interlayer spacing is 0.4-0.42 nm.

[0043] The third aspect of this application provides a lithium-ion battery, wherein the lithium-ion battery uses the carboxyl-modified graphite described in the second aspect of this application as the negative electrode material.

[0044] Unlike existing technologies, the carboxyl-modified graphite prepared by the method of this application is used as the negative electrode material. The lithium-ion battery was tested at 0.1C rate and 1C rate. The capacity at 1C rate was 2.6 times higher than that of untreated raw graphite. Moreover, at 1C rate, the capacity retention rate was significantly better than that of raw graphite after 100 cycles.

[0045] Example 1:

[0046] A carboxyl-modified porous fast-dissolving graphite and its preparation method are disclosed, comprising three processes: preparation of graphite oxide, preparation of porous graphite oxide, and preparation of carboxyl-modified graphite. Specifically:

[0047] S1: Add 5-10g of flake graphite (99.9% purity, 500 mesh) to a mixed solution of concentrated sulfuric acid (98%), fuming nitric acid (98%), and sodium chlorate in a mass ratio of 3:1:0.5, and stir slowly until completely dispersed.

[0048] S2: The mixture obtained in S1 was magnetically stirred at room temperature for 4 hours. Then, the product after acid treatment was purified by filtration and washing to obtain graphite oxide.

[0049] S3: Add a certain volume of pure water to 5g of graphite oxide prepared in S2, and then mix it with 1.5mL of 30% H2O2 by volume and stir until homogeneous.

[0050] S4: The mixed solution obtained in S3 was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180°C for 4 hours. After the reaction was complete, it was cooled to room temperature. The hydrothermal reaction product was then washed and filtered to obtain porous graphite oxide.

[0051] S5: Weigh 5g of the porous graphite oxide prepared in S4, add a certain volume of pure water, stir evenly, then add 6.5g of sodium hydroxide (NaOH, 95%) and 5g of chloroacetic acid (ClCH2COOH, 98%) sequentially, and stir magnetically at room temperature for 3 hours until the reaction is complete. The product is then washed until the pH of the washing solution is close to 7 to obtain the carboxylated porous fast-dissolving graphite.

[0052] Example 2:

[0053] The difference between Example 2 and Example 1 is that the amount of H2O2 with a volume fraction of 30% in S3 is 3 mL, and then the hydrothermal reaction is carried out at 180°C for 4 h, while other conditions and parameters remain unchanged.

[0054] Example 3:

[0055] The difference between Example 3 and Example 1 is that the hydrothermal reaction time in S4 is 6 hours, while other conditions and parameters remain unchanged.

[0056] The graphite materials in Examples 1-3 are densely covered with pores ranging from 30 nm to 2 μm in size, with a graphite interlayer spacing of 0.4-0.42 nm. X-ray photoelectron spectroscopy (XPS) was used to characterize the graphite samples from Example 3 after different stages of treatment, and the compositional changes were analyzed. The data results are shown in Table 1.

[0057] Table 1. XPS composition and content of graphite at different treatment stages.

[0058]

[0059] Comparative Example 1:

[0060] Comparative Example 1 differs from Example 1 in that it does not undergo oxidation treatment, H2O2 porous modification, or carboxyl functionalization modification. The specific method is as follows:

[0061] S1: Add 5-10g of flake graphite (99.9% purity, 500 mesh) to a certain volume of pure water (to make it the same volume as the hydrothermal reaction in step S4 of Example 1), and stir until homogeneous.

[0062] S2: The mixed solution obtained in S1 was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180°C for 4 hours. After the reaction was complete, it was cooled to room temperature. The hydrothermal reaction product was then washed and filtered to obtain hydrothermally treated graphite.

[0063] S3: Weigh 5g of the graphite prepared in S2, add a certain volume of pure water, stir evenly, then add 6.5g of sodium hydroxide (NaOH, 95%) and 5g of chloroacetic acid (ClCH2COOH, 98%) sequentially, and stir magnetically at room temperature for 3 hours until the reaction is complete. The product is then washed and filtered until the pH of the washing solution is close to 7, yielding the negative electrode graphite material.

[0064] Comparative Example 2:

[0065] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not undergo carboxyl functionalization modification. The specific method is as follows:

[0066] S1: Add 5-10g of flake graphite (99.9% purity, 200 mesh) to a mixed solution of concentrated sulfuric acid (98%), fuming nitric acid (98%), and sodium chlorate in a mass ratio of 3:1:0.5, and stir slowly until completely dispersed.

[0067] S2: The mixture obtained in S1 was magnetically stirred at room temperature for 4 hours. Then, the product after acid treatment was purified by filtration and washing to obtain graphite oxide.

[0068] S3: Add a certain volume of pure water to 5g of graphite oxide prepared in S2, and then mix it with 1.5mL of 30% H2O2 by volume and stir until homogeneous.

[0069] S4: The mixed solution obtained in S3 was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180°C for 4 hours. After the reaction was complete, it was cooled to room temperature. The hydrothermal reaction product was then washed and filtered to obtain the negative electrode graphite material.

[0070] Comparative Example 3:

[0071] This embodiment differs from Embodiment 1 in that it does not involve H2O2 pore modification. The specific method is as follows:

[0072] S1: Add 5-10g of flake graphite (99.9% purity, 200 mesh) to a mixed solution of concentrated sulfuric acid (98%), fuming nitric acid (98%), and sodium chlorate in a mass ratio of 3:1:0.5, and stir slowly until completely dispersed.

[0073] S2: The mixture obtained in S1 was magnetically stirred at room temperature for 4 hours. Then, the product after acid treatment was purified by filtration and washing to obtain graphite oxide.

[0074] S3: Add a certain volume of pure water to the 5g of graphite oxide prepared in S2 (make it the same volume as the hydrothermal reaction in step S4 of Example 1), and stir until homogeneous.

[0075] S4: The mixed solution obtained in S3 was transferred to a polytetrafluoroethylene reactor and hydrothermally reacted at 180°C for 4 hours. After the reaction was complete, it was cooled to room temperature. The hydrothermal reaction product was then washed and filtered to obtain porous graphite oxide.

[0076] S5: Weigh 5g of the porous graphite oxide prepared in S4, add a certain volume of pure water, stir evenly, then add 6.5g of sodium hydroxide (NaOH, 95%) and 5g of chloroacetic acid (ClCH2COOH, 98%) sequentially, and stir magnetically at room temperature for 3 hours until the reaction is complete. Then wash and filter the above product to obtain the negative electrode graphite material.

[0077] Performance testing:

[0078] Take 5g of the negative electrode graphite material obtained in Examples 1-3 and Comparative Examples 1-3, add it to 20g of pure water, stir evenly, and measure its sedimentation time to evaluate its dispersibility. Since the dispersibility varies greatly among different samples, the samples are allowed to stand, and the sedimentation time is recorded when graphite deposits at the same location. The test method and results are as follows: Figure 2 As shown.

[0079] It is worth noting that because the original graphite particles are not uniform in size, and the preparation process can lead to a reduction in the particle size of some graphite particles (such as H2O2 etching), the carboxylated graphite (Examples 1-3, Comparative Example 3) exhibits a sedimentation phenomenon that is significantly different from that of the original graphite. Figure 3 The images show graphite products from different embodiments after standing in an aqueous environment for 20 minutes. Carboxylated graphite exhibits inconspicuous stratification, although the time taken for the large graphite particles at the bottom to settle to the same position is not significantly different from that of the original graphite. Figure 2 However, the smaller particles or particles with more polar functional groups in the upper layer are still uniformly dispersed in water. This indicates that the dispersibility of carboxylated graphite is far superior to that of original graphite.

[0080] To verify the improvement effect of the carboxyl-modified graphite as a battery anode material compared with the inherent defects of the original graphite anode, the anode graphite materials obtained in Examples 1-3 and Comparative Examples 1-3 were assembled into coin cells for lithium-ion battery key performance testing. The testing parameters and specific methods are as follows:

[0081] Constant current charge-discharge test. The specific test method is as follows: After the newly packaged button cell battery is placed in a glove box for 12 hours, it is connected to the battery testing system to perform a constant current charge-discharge test. The voltage is uniformly set to 0.013V, and the current setting is calculated according to the charge-discharge rate and the theoretical capacity value of the graphite anode material.

[0082] Soft-pack battery testing. Considering the extremely poor dispersibility of the original stone mill and to verify the compatibility of the preparation method with the commercial preparation process of traditional graphite anode materials, a small amount of sodium carboxymethyl cellulose (CMC) dispersant was added to all anode coatings to assist dispersion. Specifically, the anode material, CMC, polystyrene-butadiene copolymer (SBR), and conductive carbon (SP) were mixed uniformly in an aqueous solution at a mass ratio of 96.7:1.1:1.5:0.7. This mixture was then coated onto copper foil, dried at 80°C, and rolled and slit to form a negative electrode sheet. Lithium foil was used as the counter electrode, a polypropylene membrane as the separator, and the electrolyte was prepared by mixing 1M lithium hexafluorophosphate (LiPF6) with ethylene carbonate (EC), diethyl carbonate (DCE), and ethyl methyl carbonate (EMC) in a 1:1:1 ratio. Electrodes made of different materials were tested using battery testing equipment at charge-discharge rates from 0.2 to 1C. The corresponding test parameter results are shown in Table 2.

[0083] Table 2 Electrochemical parameters of lithium-ion batteries assembled with graphite materials

[0084]

[0085] In summary, the preparation method of this invention is simple, requires minimal equipment, and is low-cost, making it easy to scale up for commercial production. The fast-dissolving graphite prepared by this invention contains numerous micro- and nano-sized pores on its surface, which can significantly improve the lithium-ion insertion / extraction rate, thereby enhancing the rate performance of the battery. The nanopores on the graphite surface are formed by the gentle erosion of oxygen functional groups on the surface of graphite oxide by H2O2, without forming through-holes, thus maintaining the structural stability of the graphite. After carboxylation treatment of the porous graphite, the oxygen functional groups are further reduced, retaining only a small number of carboxyl functional groups, which greatly improves the dispersibility of graphite in aqueous solvents without significantly sacrificing battery performance. The remaining oxygen functional groups can increase the interlayer spacing of graphite, further improving the lithium-ion insertion / extraction rate, and also increasing the adhesion between the fast-dissolving graphite and the copper current collector.

[0086] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A method for preparing carboxyl-modified graphite, characterized in that, Includes the following steps: Preparation of porous graphite oxide: Add water to graphite oxide and stir to obtain a first dispersion. Mix the first dispersion with hydrogen peroxide and react hydrothermally at 160-180℃ for 3-6 hours to obtain a hydrothermal product. Separate the hydrothermal product into solid and liquid phases to obtain a first solid. Wash the first solid to obtain porous graphite oxide. Preparation of carboxyl-modified graphite: The porous graphite oxide was added to water and stirred to obtain a second dispersion; 95% sodium hydroxide and 98% chloroacetic acid were added to the second dispersion in sequence, and the mixture was stirred in a water bath for more than 3 hours to obtain a water bath product. The water bath product was separated into solid and liquid phases to obtain a second solid product. The second solid product was washed to obtain the carboxyl-modified graphite.

2. The preparation method according to claim 1, characterized in that, The preparation of the graphite oxide includes the following steps: adding flake graphite to a first mixed solution, stirring slowly until completely dispersed, and continuing to stir for 3-6 hours to obtain a third dispersion; the third dispersion is subjected to solid-liquid separation and washing to obtain graphite oxide; the first mixed solution is a mixed solution of 98% sulfuric acid, 98% nitric acid and sodium chlorate.

3. The preparation method according to claim 2, characterized in that, The mesh size of the flake graphite is 500-2000 mesh.

4. The preparation method according to claim 2, characterized in that, In the step of preparing graphite oxide, the mass ratio of 98% sulfuric acid, 98% nitric acid and sodium chlorate in the first mixed solution is 6:2:

1.

5. The preparation method according to claim 1, characterized in that, In the porous graphite oxide preparation step, the hydrogen peroxide is a hydrogen peroxide solution with a volume percentage of 30-35%.

6. The preparation method according to claim 1, characterized in that, In the preparation step of the carboxyl-modified graphite, the mass ratio of porous graphite oxide, 95% sodium hydroxide, and 98% chloroacetic acid is 10:13:

10.

7. The preparation method according to claim 1, characterized in that, In the preparation step of the carboxyl-modified graphite, the second solid is washed multiple times with distilled water until the pH of the washing solution is 6.9 to 7.

1.

8. A carboxyl-modified graphite, characterized in that, The carboxyl-modified graphite is prepared using the preparation method described in any one of claims 1-7.

9. The carboxyl-modified graphite according to claim 8, characterized in that, The carboxyl-modified graphite is densely covered with pores ranging from 30 nm to 2 μm in size, and the interlayer spacing of the graphite is 0.4-0.42 nm.

10. A lithium-ion battery, characterized in that, The lithium-ion battery uses the carboxyl-modified graphite as described in claim 9 as the negative electrode material.

Images