Graphite composite negative electrode material and preparation method thereof, negative electrode sheet and lithium battery

Abstract

This application relates to the field of lithium-ion batteries, disclosing a graphite composite anode material, its preparation method, anode sheet, and a lithium battery. The anode material comprises graphite, a conductive metal, and graphene quantum dots; the graphite forms the matrix core, coated with the conductive metal, and the graphene quantum dots coat the conductive metal. This application employs vapor deposition of the conductive metal, which can uniformly form a highly conductive metal layer on the graphite surface, improving charge / discharge capacity, enhancing charge transport performance and conductivity, resulting in a significant improvement in rate performance. Simultaneously, the simple evaporation of organic solvents allows for the uniform coating of nanoscale graphene quantum dots onto the metal / graphite composite material surface, effectively mitigating volume changes during charge / discharge and thus enhancing the rate performance and cycle stability of the composite material. Furthermore, using oil-based needle coke and pitch to prepare the graphite material can also improve the overall electrochemical performance of the anode material.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a graphite composite anode material and its preparation method, as well as an anode sheet and a lithium battery. Background Technology

[0002] With the booming development of new energy industries, lithium-ion batteries play an important role in new energy and are widely used in power batteries, energy storage batteries, and 3C batteries. Therefore, developing high-performance lithium-ion electrode materials has become a top priority in the new energy industry today.

[0003] Currently, commercially available graphite materials have advantages such as low cost, high safety, and stable cycle performance, and are widely used in lithium-ion battery anode materials. However, their capacity is low and their rate performance is poor. Therefore, researchers have carried out a series of modification treatments on graphite anode materials, including surface coating and doping, which have further improved the electrochemical performance of lithium-ion batteries.

[0004] Existing patent CN104112852A discloses a method for preparing a negative electrode material for lithium-ion batteries. This method uses a metal melting method or a mixed calcination method to coat the surface of a graphite negative electrode with a layer of elemental metal, achieving molecular-level metal coating on the graphite negative electrode surface. During formation, this negative electrode material reduces the contact area between the electrolyte and the graphite negative electrode, thereby improving the initial efficiency of the negative electrode material. It also improves the battery's cycle performance. Furthermore, due to the extremely low intermetallic contact resistance, it reduces the contact resistance between the negative electrode material and the current collector.

[0005] However, based on problems discovered during actual research and development, although this type of technology has improved the electrochemical performance of graphite-based anode materials, it still cannot meet the current requirements of lithium-ion batteries for graphite-based anode materials, especially in terms of rate performance and cycle performance. Therefore, how to improve graphite-based anode materials to further enhance the cycle performance and rate performance of lithium batteries remains an important research direction in new energy. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide a graphite composite anode material and its preparation method, so that the anode material can improve the rate performance and cycle performance of the battery;

[0007] Another objective of this application is to provide a negative electrode sheet and a lithium battery based on the aforementioned negative electrode material.

[0008] In order to solve the above-mentioned technical problems / achieve the above-mentioned objectives, or at least partially solve the above-mentioned technical problems / achieve the above-mentioned objectives, as a first aspect of this application, a graphite composite anode material is provided, comprising graphite, a conductive metal, and graphene quantum dots; wherein the graphite is the matrix core and is coated with the conductive metal, and the graphene quantum dots are coated with the conductive metal.

[0009] Optionally, the mass ratio of the graphite, conductive metal and graphene quantum dots is (100-200):(10-50):(20-60).

[0010] Optionally, the conductive metal includes one or more of zinc, copper, manganese, and iron.

[0011] As a second aspect of this application, a method for preparing the negative electrode material is provided, comprising:

[0012] Conductive metals are deposited on the surface of graphite using vapor deposition to form metal / graphite composite materials;

[0013] Graphene quantum dots and the metal / graphite composite material are dispersed in a volatile solvent. After evaporating the volatile solvent, a negative electrode material of graphene quantum dots coated with metal-deposited graphite is obtained.

[0014] Optionally, the vapor deposition method includes:

[0015] The graphite is acidified, washed and dried, then dispersed in an organic solvent. Under a protective gas atmosphere, the metal suspension is atomized and deposited.

[0016] Further optionally, the graphite is obtained by graphitizing oil-based needle coke and pitch; the organic solvent includes one or more of acetone, carbon tetrachloride, and benzene.

[0017] Optionally, the graphene quantum dots are prepared from pyrene via a nitration-hydrothermal method.

[0018] As a third aspect of this application, a negative electrode sheet is provided, using the negative electrode material described in this application or the negative electrode material prepared by the preparation method described in this application as the active material.

[0019] As a fourth aspect of this application, a lithium battery is provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the third aspect.

[0020] Compared to existing graphite-based anode materials with surface metal coatings, this application employs vapor-deposited conductive metal, which can uniformly form a highly conductive metal layer on the graphite surface. This improves charge / discharge capacity, enhances charge transport performance and the conductivity of the composite material, resulting in a significant improvement in rate performance. Simultaneously, the simple evaporation of organic solvents allows for the uniform coating of nanoscale graphene quantum dots onto the metal / graphite composite surface, effectively mitigating volume changes during charge / discharge and further enhancing the rate performance and cycle stability of the composite material. Furthermore, the use of oil-based needle coke and pitch to prepare the graphite material also improves the overall electrochemical performance of the anode material. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application.

[0022] Figure 1 The diagram shown is a structural schematic of the graphite composite anode material described in this application.

[0023] Figure 2 The image shown is a SEM image of the artificial graphite prepared in this application using oil-based needle coke and pitch as raw materials.

[0024] Figure 3 The images shown are TEM and XRD patterns of graphene quantum dots prepared using pyrene as a raw material in this application. Detailed Implementation

[0025] This application discloses a graphite composite anode material and its preparation method, as well as an anode sheet and a lithium battery. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products, processes, and applications described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the methods described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0026] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0027] This application uses artificial graphite as the matrix core, and employs vapor deposition of conductive metal to form a metal / C composite material. Then, using pyrene as a raw material, it is acidified with nitric acid to obtain 1,3,6-trinitropyrene (C). 16 H7N3O6) was then ultrasonically dispersed in NaOH solution and followed by hydrothermal synthesis of graphene quantum dots. The metal / C composite material and graphene quantum dots were then ultrasonically dispersed in volatile solvents such as ethanol. Finally, the solvent was evaporated to obtain a negative electrode material of graphene quantum dots coated with metal-deposited graphitized carbon. Using this negative electrode material as a negative electrode can improve the capacity, rate performance and charge-discharge cycle performance of commercial artificial graphite negative electrode materials, thus effectively improving the cost and performance of lithium batteries.

[0028] In the first aspect of this application, a graphite composite anode material is provided, comprising graphite, a conductive metal, and graphene quantum dots; the graphite forms the matrix core, which is coated with the conductive metal, and the graphene quantum dots coat the conductive metal. A schematic diagram of its structure is shown below. Figure 1 .

[0029] In some embodiments of this application, the mass ratio of graphite, conductive metal, and graphene quantum dots is (100-200):(10-50):(20-60). In other embodiments of this application, the mass ratio of graphite, conductive metal, and graphene quantum dots is 100:10:20, 100:50:30, 100:20:20, 120:30:20, 200:50:40, or 100:10:60.

[0030] In some embodiments of this application, the conductive metal includes one or more of zinc, copper, manganese, and iron; the graphite includes artificial graphite, such as artificial graphite prepared using oil-based needle coke and pitch; and the graphene quantum dots include graphene quantum dots prepared using pyrene as a raw material.

[0031] In a second aspect of this application, a method for preparing the negative electrode material is provided, comprising:

[0032] Conductive metals are deposited on the surface of graphite using vapor deposition to form metal / graphite composite materials;

[0033] Graphene quantum dots and the metal / graphite composite material are dispersed in a volatile solvent. After evaporating the volatile solvent, a negative electrode material of graphene quantum dots coated with metal-deposited graphite is obtained.

[0034] In some embodiments of this application, the vapor deposition method includes: acidifying graphite, washing and drying it, then dispersing it in an appropriate amount of organic solvent, and atomizing and depositing the metal suspension under a protective gas atmosphere. In other embodiments of this application, the mass ratio of graphite to metal is (100-200):(10-50), for example, 100:10, 100:20, 100:50, 120:30, or 200:50.

[0035] In some other embodiments of this application, concentrated nitric acid is used to acidify the graphite in the vapor deposition method; more specifically, the mass-to-volume ratio of graphite to concentrated nitric acid is 5g:10-15mL; in some other embodiments of this application, the vapor deposition is carried out under vacuum and heating conditions, for example, a vacuum degree of 100-150 Pa and a heating temperature of 180-200℃; the deposition time is 10-15 min; in some other embodiments of this application, the protective gas includes nitrogen and inert gases, such as argon, helium, etc.; the organic solvent includes one or more of acetone, carbon tetrachloride, and benzene. In some embodiments of this application, the graphite is obtained by graphitizing oil-based needle coke and pitch; in other embodiments, the mass ratio of the oil-based needle coke to pitch is (8-10):(1-2), for example, 8:1, 8:1.5, 8:2, 9:1, 9:1.5, 9:2, 10:1, 10:1.5, or 10:2. In still other embodiments, the graphitization is performed at a high temperature of 2700℃-2900℃.

[0036] Graphene quantum dots generally have a lateral dimension of less than 100 nm and a longitudinal dimension of less than a few nanometers, possessing a single, double, or multiple layers of graphene structure. They can be prepared using different raw materials and processes, which this application does not limit. In some embodiments of this application, pyrene is used as the raw material for preparation via a hydrothermal nitration method. In other embodiments of this application, the graphene quantum dots can be prepared using the following process:

[0037] Using 1-2g of pyrene as raw material, 1,3,6-trinitropyrene was obtained by acidification with 150-200mL of concentrated nitric acid. Then, 1-2g of 1,3,6-trinitropyrene was dispersed in 300-500mL of 0.2mol / L NaOH solution and heated at 190-200℃ for 12 hours. After cooling to room temperature, impurities and unreacted small molecules were removed from the resulting suspension, and the graphene quantum dots were obtained after drying.

[0038] In some embodiments of this application, during the graphene quantum dot coating process, the graphene quantum dots and the metal / graphite composite material are dispersed in a certain volume of volatile solvent at a mass ratio of 20-60:110-250. The mixture is continuously stirred and the volatile solvent is evaporated. After evaporation to dryness, the coating of the metal / graphite composite material with graphene quantum dots is completed. In other embodiments of this application, the volatile solvent includes ethanol and / or acetone. In other embodiments of this application, the mass ratio of the graphene quantum dots to the metal / graphite composite material can be 20:110, 20:120, 20:150, 30:150, 40:250, or 60:110, etc.

[0039] In some embodiments of this application, the preparation method of the graphite composite anode material includes:

[0040] Oil-based needle coke and pitch are mixed and ground to micron level in a certain proportion, and then graphitized at 2700℃-2900℃ to obtain artificial graphite. The artificial graphite is then acidified in concentrated nitric acid, washed and dried, and then dispersed in an organic solvent and transferred into a reaction chamber. Under an inert atmosphere and a vacuum of 100 Pa, it is heated to 180℃-200℃. First, the metal suspension is atomized through a gas path and introduced into the reaction chamber for deposition, thus obtaining a metal / graphite composite material with metal deposition.

[0041] 1-2 g of pyrene was placed in a container containing 150-200 mL of concentrated nitric acid and refluxed at 75 °C for 15-18 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and then filtered to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1-2 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300-500 mL of 0.2 mol / L NaOH solution, then transferred to a hydrothermal reactor and heated at 190-200 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered and dialyzed to remove impurities and unreacted small molecules, and then dried to obtain graphene quantum dots (GQDs).

[0042] A certain amount of GQDs was ultrasonically dispersed in a certain volume of volatile solvent, and then the metal / graphite composite material was slowly added. The mixture was continuously stirred while the volatile solvent was evaporated. After evaporation to dryness, the mixture was dried, completing the coating of the metal / graphite composite material with graphene quantum dots, thus obtaining the graphite composite anode material.

[0043] In a third aspect of this application, a negative electrode sheet is provided, using the graphite composite negative electrode material described in this application as the active material or the graphite composite negative electrode material prepared by the preparation method described in this application as the active material.

[0044] In some embodiments of this application, the negative electrode sheet includes a current collector and an active material coated on the current collector; wherein, the current collector may be selected from a metal foil with good conductivity, such as copper foil; the active material includes the negative electrode material described in this application, as well as a binder, a conductive agent, and a solvent. The binder, conductive agent, and solvent, and their amounts, are selected in accordance with conventional methods, and this application does not impose specific limitations. For example, the binder may be polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), LA132 binder, and sodium carboxymethyl cellulose (CMC), etc.; the conductive agent may be conductive carbon black (SP), acetylene black, etc.; and the solvent may be N-methylpyrrolidone (NMP), deionized water, etc. The ratio of negative electrode material: conductive agent: binder: solvent is 95g:1g:4g:220mL.

[0045] In a fourth aspect of this application, a lithium battery is provided, including a positive electrode, a separator, an electrolyte, and the negative electrode described in this application; in some embodiments of this application, the lithium-ion battery is a full cell, a pouch cell, or a button cell.

[0046] In some embodiments of this application, the positive electrode is a lithium metal sheet or lithium iron phosphate, high-nickel ternary, lithium-rich manganese-based material, etc.; the separator is a Celegard series separator, polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane; the electrolyte is a 1.0-1.5 mol / L LiPF6 solution, for example, a LiPF6 electrolyte with a volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents of 1:1.

[0047] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0048] The following provides a further description of a graphite composite anode material, its preparation method, anode sheet, and lithium battery provided in this application.

[0049] Example 1:

[0050] 80g of oil-based needle coke and 20g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2800℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. Then, 50g of artificial graphite was placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 5h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of acetone and transferred into a reaction chamber. Under an argon atmosphere and a vacuum of 100pa, the mixture was heated to 180℃. First, 20g of metallic Cu suspension (Cu mass fraction of 25%) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. Finally, a metal / graphite composite material was obtained.

[0051] pyrene (C 16 H 10 1.0 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 200 mL of concentrated nitric acid (HNO3, 65%) and refluxed at 75 °C for 16 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and then filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300 mL of 0.2 M NaOH solution (ultrasonication for 3 hours), then transferred to a 100 mL hydrothermal reactor and heated at 190 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0052] 2g of the prepared GQDs were ultrasonically dispersed in anhydrous ethanol. Then, 11g of metal / graphite composite material was added while stirring continuously. After stirring for 1.5h, the mixture was transferred to a water bath and stirred continuously at 75℃ to evaporate the solvent. After the ethanol was completely evaporated, the mixture was transferred to a vacuum drying oven at 80℃ for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots is 100:10:20).

[0053] Example 2:

[0054] 80g of oil-based needle coke and 15g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2800℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. Then, 50g of artificial graphite was placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 3h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of carbon tetrachloride and transferred into a reaction chamber. Under a nitrogen atmosphere and a vacuum of 100pa, the mixture was heated to 200℃. First, 100g of metallic Zn suspension (Zn mass fraction of 25%) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. Finally, a metal / graphite composite material was obtained.

[0055] pyrene (C 16 H 10 1.0 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 150 mL of concentrated nitric acid (HNO3, 65%) and refluxed at 75 °C for 17 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and then filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300 mL of 0.4 M NaOH solution (ultrasonication for 5 hours), then transferred to a 100 mL hydrothermal reactor and heated at 200 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0056] 3g of the prepared GQDs were ultrasonically dispersed in acetone. Then, 15g of metal / graphite composite material was added while stirring continuously. After stirring for another 1 hour, the mixture was transferred to a water bath and stirred continuously at 70°C to evaporate the solvent. After the acetone was completely evaporated, the mixture was transferred to a vacuum drying oven at 80°C for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots is 100:50:30).

[0057] Example 3

[0058] 80g of oil-based needle coke and 10g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2900℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. 50g of artificial graphite was then placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 5h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of benzene and transferred to a reaction chamber. Under an argon atmosphere and a vacuum of 100pa, the mixture was heated to 200℃. First, 40g of a suspension of metallic Mn (25% by mass) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. A metal / graphite composite material was then obtained.

[0059] pyrene (C 16 H 10 2 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 150 mL of concentrated nitric acid (HNO3, 65%). The mixture was refluxed at 75 °C for 16 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and then filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 500 mL of 0.3 M NaOH solution (ultrasonication for 3 hours), then transferred to a 100 mL hydrothermal reactor and heated at 190 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0060] 2g of the prepared GQDs were ultrasonically dispersed in anhydrous ethanol. Then, 12g of metal / graphite composite material was added while stirring continuously. After stirring for 1.5h, the mixture was transferred to a water bath and stirred continuously at 80℃ to evaporate the solvent. After the anhydrous ethanol was completely evaporated, the mixture was transferred to a vacuum drying oven at 80℃ for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots is 100:20:20).

[0061] Example 4:

[0062] 80g of oil-based needle coke and 15g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2800℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. Then, 50g of artificial graphite was placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 3h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of carbon tetrachloride and transferred into a reaction chamber. Under a nitrogen atmosphere and a vacuum of 100pa, the mixture was heated to 200℃. First, 50g of metallic Fe suspension (Fe mass fraction of 25%) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. Finally, a metal / graphite composite material was obtained.

[0063] pyrene (C 16 H 101.0 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 150 mL of concentrated nitric acid (HNO3, 65%) and refluxed at 75 °C for 17 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300 mL of 0.4 M NaOH solution (ultrasonication for 5 hours), then transferred to a 100 mL hydrothermal reactor and heated at 200 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0064] 2g of the prepared GQDs were ultrasonically dispersed in ethanol, and then 15g of metal / graphite composite material was added while stirring continuously. After stirring for another 1 hour, the mixture was transferred to a water bath and stirred continuously at 70°C to evaporate the solvent. After the ethanol was completely evaporated, the mixture was transferred to a vacuum drying oven at 80°C for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots is 120:30:20).

[0065] Example 5:

[0066] 90g of oil-based needle coke and 10g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2800℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. Then, 50g of artificial graphite was placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 5h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of acetone and transferred into a reaction chamber. Under an argon atmosphere and a vacuum of 100pa, the mixture was heated to 180℃. First, 20g of metallic Cu suspension (Cu mass fraction of 25%) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. Finally, a metal / graphite composite material was obtained.

[0067] pyrene (C 16 H 101.0 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 200 mL of concentrated nitric acid (HNO3, 65%) and refluxed at 75 °C for 16 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 1.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300 mL of 0.2 M NaOH solution (ultrasonication for 3 hours), then transferred to a 100 mL hydrothermal reactor and heated at 190 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0068] 6g of the prepared GQDs were ultrasonically dispersed in anhydrous ethanol. Then, 11g of metal / graphite composite material was added while stirring continuously. After stirring for 1.5h, the mixture was transferred to a water bath and stirred continuously at 75℃ to evaporate the solvent. After the ethanol was completely evaporated, the mixture was transferred to a vacuum drying oven at 80℃ for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots is 100:10:60).

[0069] Example 6:

[0070] 100g of oil-based needle coke and 20g of pitch were ground to a particle size of about 10 micrometers. The two types of coke were then mixed evenly and graphitized at 2800℃. After cooling, sieving, and demagnetizing, artificial graphite was obtained. Then, 50g of artificial graphite was placed in 20ml of concentrated nitric acid (65%) and magnetically stirred for 5h. After washing and drying, the acidified artificial graphite was dispersed in 15ml of acetone and transferred into a reaction chamber. Under an argon atmosphere and a vacuum of 100pa, the mixture was heated to 180℃. First, 50g of metallic Cu suspension (Cu mass fraction of 25%) was atomized through a gas path and introduced into the reaction chamber, where it was deposited for 15min. Finally, a metal / graphite composite material was obtained.

[0071] pyrene (C 16 H 102.0 g of 1,3,6-trinitropyrene was placed in a round-bottom flask containing 200 mL of concentrated nitric acid (HNO3, 65%) and refluxed at 75 °C for 16 hours with stirring. After cooling to room temperature, the mixture was diluted with deionized water and then filtered through a 0.22 μm microporous membrane to remove the nitric acid, yielding yellow 1,3,6-trinitropyrene. 2.0 g of 1,3,6-trinitropyrene was ultrasonically dispersed in 300 mL of 0.2 M NaOH solution (ultrasonication for 3 hours), then transferred to a 100 mL hydrothermal reactor and heated at 190 °C for 12 hours. After cooling to room temperature, the resulting suspension was filtered through a 0.22 μm microporous membrane to remove impurities and further dialyzed in a dialysis bag for 3 days to remove sodium salts and small molecules that did not form graphene quantum dots. The purified GQDs were dried at 80 °C.

[0072] 4g of the prepared GQDs were ultrasonically dispersed in anhydrous ethanol. Then, 25g of metal / graphite composite material was added while stirring continuously. After stirring for 1.5h, the mixture was transferred to a water bath and stirred continuously at 75℃ to evaporate the solvent. After the ethanol was completely evaporated, the mixture was transferred to a vacuum drying oven at 80℃ for further drying to obtain the graphite composite anode material (the mass ratio of graphite, conductive metal and graphene quantum dots was 200:50:40).

[0073] Comparative Example 1:

[0074] The difference compared to Example 1 is as follows:

[0075] (1) Replace 80g of oil-based needle coke and 20g of pitch with 60g of oil-based needle coke and 30g of pitch;

[0076] (2) Change 2g GQDs to 1.5g GQDs;

[0077] (3) The 11g metal / graphite composite material was changed to 26g metal / graphite composite material.

[0078] Comparative Example 2:

[0079] The difference compared to Example 1 is as follows:

[0080] (1) The vacuum drying oven was replaced with a regular drying oven and heated to 100℃ for drying.

[0081] Comparative Example 3:

[0082] The difference compared to Example 1 is as follows:

[0083] (1) Instead of atomizing the Cu metal suspension and introducing it into the reaction chamber, we would atomize the Sn metal suspension (Sn mass fraction is 25%) and introduce it into the reaction chamber.

[0084] Comparative Example 4:

[0085] The difference compared to Example 1 is as follows:

[0086] (1) Grinding 80g of oil-based needle coke and 20g of asphalt to a particle size of about 10 micrometers is changed to grinding 80g of oil-based non-needle coke and 20g of asphalt to a particle size of about 10 micrometers.

[0087] Comparative Example 5:

[0088] The difference compared to Example 1 is as follows:

[0089] (1) Only the metal / graphite composite material was obtained, without the subsequent preparation of graphene quantum dots and the coating of the metal / graphite composite material.

[0090] Comparative Example 6:

[0091] The difference compared to Example 1 is as follows:

[0092] (1) No metal deposition is performed; graphene quantum dots are used directly for coating.

[0093] Experimental Example 1:

[0094] 1. Morphological characteristics

[0095] The artificial graphite prepared in Example 1 was subjected to SEM testing and GODs were subjected to TEM and XRD testing. The test results are as follows: Figures 2-3 As shown.

[0096] Depend on Figure 2 It can be seen that the artificial graphite particles are between 10-20μm in size, and the particles are uniform and have regular shapes.

[0097] Depend on Figure 3 It can be seen that the GQDs prepared in Example 1 have a particle size of 1-10 nm, uniform particle size, and good characteristic peaks.

[0098] 2. Powder conductivity test

[0099] The negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-6 were pressed into block structures, and then the conductivity of the powder was tested using a four-probe tester. The test results are shown in Table 1.

[0100] Table 1

[0101] Project / Number Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Powder conductivity (S / m) 1.16 1.17 1.05 1.13 1.18 1.16 Project / Number Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Powder conductivity (S / m) 1.03 1.12 1.11 0.89 0.87 0.91

[0102] Table 1 shows that the negative electrode materials in each embodiment of this application all have high electrical conductivity; however, the negative electrode materials in the comparative examples prepared based on Example 1 show a decrease in powder electrical conductivity compared to the negative electrode material in Example 1. This indicates that Example 1 of this application effectively deposits conductive metal Cu on the surface of artificial graphite, including good deposition between graphite layers, resulting in good contact between the metal and graphite, thereby significantly improving the electrical conductivity of the graphite composite negative electrode material. At the same time, the synergistic effect of GQDs also significantly improves the electrical conductivity of the composite material.

[0103] 3. Button cell battery test

[0104] The negative electrode materials obtained in Examples 1-6 and Comparative Examples 1-6 were assembled into coin cells. The preparation method was as follows: the negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-6 were used as active materials, Super-P was used as a conductive agent, and LA132 was used as a binder. The ratio of active material: Super-P: LA132: double-distilled water = 95g: 1g: 4g: 220mL was mixed and stirred evenly, coated on copper foil, vacuum dried at 80℃ for 12h, and then cut into circles to obtain negative electrode sheets.

[0105] Using LiPF6 / EC+DEC (volume ratio 1:1, concentration 1.2mol / L) as the electrolyte, lithium metal sheets as the reference and counter electrodes, and polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membranes as the separator, the simulated battery was assembled in an argon-filled glove box. Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The rate capability (2C / 0.1C) and cycle performance (0.2C / 0.2C, 400 cycles) of the coin cells were also tested. The test results are shown in Table 2 below.

[0106] Table 2

[0107]

[0108]

[0109] As can be seen from Table 2, the anode materials of each embodiment of this application exhibit higher electrochemical performance, particularly in rate performance and cycle performance, which are significantly superior to those of the comparative examples. The anode materials of the comparative examples prepared based on Example 1 show a decline in various performance characteristics compared to the anode material of Example 1.

[0110] 4. Soft-pack battery test

[0111] Negative electrode sheets were prepared using the negative electrode materials from Examples 1-6 and Comparative Examples 1-6. Ternary materials (LiNi) were used. 1 / 3Co1 / 3 Mn 1 / 3 Using O2 as the positive electrode, a LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.2 mol / L) as the electrolyte, and a Celegard 2400 membrane as the separator, 2Ah pouch cells A-1, A-2, A-3, A-4, A-5, A-6 and B-1, B-2, B-3, B-4, B-5, B-6 were prepared. The cycle performance and rate performance of the pouch cells were then tested.

[0112] Rate performance test conditions: charging rate: 1C / 2C / 3C / 5C, discharging rate: 1C; voltage range: 2.6-4.2V, temperature: 25±3℃. The constant current ratio of the battery was tested, and the test results are shown in Table 3.

[0113] The cyclic test conditions were: charge / discharge rate 2C / 2C, voltage range: 2.6-4.2V, temperature: 25±3℃, number of cycles: 800; the test results are shown in Table 3.

[0114] Table 3

[0115]

[0116]

[0117] As can be seen from Table 3, the soft-pack battery prepared by the graphite composite anode material of this application has a better constant current ratio, which is significantly better than that of the comparative examples, and has higher cycle performance, which is better than that of the comparative examples overall. In addition, the anode materials of the comparative examples prepared based on Example 1 show a significant decrease in rate performance and cycle performance compared with the anode material of Example 1.

[0118] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A graphite composite anode material, characterized in that, It includes graphite, conductive metal, and graphene quantum dots; the graphite is the matrix core, coated with conductive metal, and the graphene quantum dots are coated with conductive metal; the mass ratio of graphite, conductive metal, and graphene quantum dots is (100-200):(10-50):(20-60); the conductive metal includes one or more of zinc, copper, manganese, and iron. The method for preparing the graphite composite anode material includes: Graphite is obtained by graphitizing oil-based needle coke and pitch, and conductive metal is deposited on the surface of the graphite using a vapor deposition method to form a metal / graphite composite material; the mass ratio of the oil-based needle coke to pitch is (8-10): (1-2). Graphene quantum dots were prepared from pyrene via a nitration-hydrothermal method. The graphene quantum dots were dispersed in a certain volume of volatile solvent at a mass ratio of 20-60:110-250 to the metal / graphite composite material. The mixture was stirred continuously while the volatile solvent was evaporated. After the solvent was completely evaporated, the mixture was vacuum dried at 80°C to complete the coating of the metal / graphite composite material with graphene quantum dots.

2. The method for preparing the negative electrode material according to claim 1, characterized in that, include: Graphite is obtained by graphitizing oil-based needle coke and pitch, and conductive metal is deposited on the surface of the graphite using a vapor deposition method to form a metal / graphite composite material. The mass ratio of the oil-based needle coke to the pitch is (8-10): (1-2). Graphene quantum dots were prepared from pyrene via a nitration-hydrothermal method. The graphene quantum dots were dispersed in a certain volume of volatile solvent at a mass ratio of 20-60:110-250 to the metal / graphite composite material. The mixture was stirred continuously while the volatile solvent was evaporated. After the solvent was completely evaporated, the mixture was vacuum dried at 80°C to complete the coating of the metal / graphite composite material with graphene quantum dots.

3. The preparation method according to claim 2, characterized in that, The vapor deposition method includes: The graphite is acidified, washed and dried, then dispersed in an organic solvent. Under a protective gas atmosphere, the metal suspension is atomized and deposited.

4. The preparation method according to claim 3, characterized in that, The organic solvent includes one or more of acetone, carbon tetrachloride, and benzene.

5. A negative electrode sheet, characterized in that, The negative electrode material according to claim 1 or the negative electrode material prepared by any one of claims 2-4 is used as the active material.

6. A lithium battery, characterized in that, It includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in claim 5.

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