Graphite negative electrode material, preparation method therefor and use thereof, and lithium-ion battery

Abstract

Disclosed are a graphite negative electrode material, a preparation method therefor and a use thereof, and a lithium-ion battery. The preparation method for the graphite negative electrode material comprises the following steps: (1) dissolving chitosan in a solvent to obtain a chitosan solution, and adding graphite and supercritical fluid-exfoliated graphene into the chitosan solution for mixing to obtain a mixture; and (2) drying the mixture, and then performing carbonization treatment to obtain the graphite negative electrode material.

Description

A graphite negative electrode material and its preparation method and application, lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese Patent Application No. 2024100342144 filed in China on January 9, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of batteries, and in particular, to a graphite negative electrode material, a preparation method and application thereof, and a lithium-ion battery. Background Art

[0004] The development of portable and telecommunications electronics requires efficient energy storage systems. Lithium-ion batteries (LIBs) are considered one of the most promising energy storage applications due to their high energy conversion and storage efficiencies. Lithium-ion batteries are experiencing continued growth and are finding applications in an ever-expanding range of fields. The development of current and future transportation, such as electric vehicles, and high-performance electronics is driving a growing demand for high-capacity lithium batteries across a wide range of devices.

[0005] In 2004, Novoselov et al. created graphene using an artificial exfoliation method, sparking a worldwide research boom. Graphene is a two-dimensional material just one carbon atom thick (0.35 nm). At room temperature, graphene conducts electrons faster than any other known conductor.

[0006] Currently, the electrochemical performance of negative electrode materials is in urgent need of improvement and enhancement. Therefore, it is of great significance to study the modification of lithium-ion battery electrode materials and develop new lithium-ion battery negative electrode materials. Summary of the Invention

[0007] The present disclosure is based on the inventors' discovery and understanding of the following facts and problems: Currently, the electrochemical performance of negative electrode materials is in urgent need of improvement and enhancement. Therefore, it is of great significance to study the modification of lithium-ion battery electrode materials and develop new lithium-ion battery negative electrode materials.

[0008] The present disclosure aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, the embodiments of the present disclosure provide a graphite negative electrode material, a preparation method and application thereof, and a lithium-ion battery. Graphene exfoliated from a supercritical fluid is composited with graphite through bonding, coating, and carbonization of chitosan in a molten state at high temperature to construct a channel-rich structured negative electrode material, thereby realizing the preparation of a graphite negative electrode material with multiple lithium storage channels, improving the conductivity of the graphite negative electrode material, promoting lithium ion transmission, and improving the rate performance and cycle performance of the lithium-ion battery.

[0009] A first embodiment of the present disclosure provides a method for preparing a graphite negative electrode material, comprising the following steps:

[0010] (1) dissolving chitosan in a solvent to obtain a chitosan solution; adding graphite and supercritical fluid exfoliated graphene to the chitosan solution and mixing them to obtain a mixture;

[0011] (2) The mixture is dried and then carbonized to obtain a graphite negative electrode material.

[0012] The advantages and technical effects of the method for preparing the graphite negative electrode material of the disclosed embodiment include: chitosan is preferably coated on the surface of graphite and supercritical fluid-exfoliated graphene by mixing using a solution method, resulting in a complete coating layer, which is beneficial to improving the overall performance of the graphite negative electrode material. The supercritical fluid-exfoliated graphene is composited with graphite through the bonding, coating, and carbonization of chitosan in a molten state at high temperature, constructing a channel-rich structured negative electrode material, achieving the preparation of a graphite negative electrode material with multiple lithium storage channels, improving the conductivity of the graphite negative electrode material, promoting lithium ion transport, and enhancing the rate performance and cycle performance of lithium-ion batteries.

[0013] In some embodiments, in step (1), the method for preparing supercritical fluid exfoliated graphene includes: mixing graphite and supercritical CO2, performing fluid shearing, and then discharging CO2 through pressure relief to obtain supercritical fluid exfoliated graphene.

[0014] In some embodiments, the fluid is sheared at a temperature of 44-62°C.

[0015] In some embodiments, the fluid shear pressure is 8.6-11.3 MPa.

[0016] In some embodiments, the fluid shearing speed is 1600-2400 r / min.

[0017] In some embodiments, the fluid is sheared for 15-60 minutes.

[0018] In some embodiments, in step (1), the graphite includes natural flake graphite.

[0019] In some embodiments, in step (1), the particle size of the graphite is 70-100 μm.

[0020] In some embodiments, in step (1), the viscosity of the chitosan is 200-500 mPa·s.

[0021] In some embodiments, in step (1), the solvent is a non-oxidizing acid.

[0022] In some embodiments, in step (1), the non-oxidizing acid includes at least one of hydrochloric acid, sulfuric acid, and citric acid.

[0023] In some embodiments, in step (1), the ratio of chitosan to solvent is 1-3 g: 200-300 mL.

[0024] In some embodiments, in step (1), the ratio of the mass of the graphite and supercritical fluid exfoliated graphene to the mass of chitosan is 20:1-3.

[0025] In some embodiments, in step (1), the mass percentage of the graphite and supercritical fluid exfoliated graphene is 0.01-10%.

[0026] In some embodiments, in step (2), the carbonization treatment adopts programmed temperature rise; the programmed temperature rise includes: heating to 800-900°C at a heating rate of 3-8°C / min, then heating to 1000-1200°C at a heating rate of 1-3°C / min, and keeping warm for 1-3h.

[0027] In some embodiments, in step (2), the particle size of the graphite negative electrode material is 10-70 μm.

[0028] A second embodiment of the present disclosure provides a graphite negative electrode material, prepared using the preparation method described in any embodiment of the first embodiment of the present disclosure. In this embodiment, supercritical fluid-exfoliated graphene is composited with graphite through bonding, coating, and carbonization of molten chitosan at high temperature to construct a channel-rich negative electrode material. This enables the preparation of a graphite negative electrode material with multiple lithium storage channels, improves the conductivity of the graphite negative electrode material, promotes lithium ion transport, and enhances the rate capability and cycling performance of lithium-ion batteries.

[0029] The third embodiment of the present disclosure provides an application of the graphite negative electrode material of any embodiment of the second aspect of the present disclosure, wherein the graphite negative electrode material is used in a lithium-ion battery. In the embodiment of the present disclosure, all advantages of the graphite negative electrode material are possessed, which will not be repeated here.

[0030] A fourth embodiment of the present disclosure provides a lithium-ion battery, comprising the graphite negative electrode material described in any embodiment of the second aspect of the present disclosure. The present embodiment has all the advantages of the graphite negative electrode material, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a SEM image of the negative electrode materials of Comparative Example 2 and Example 1 according to the present disclosure.

[0032] FIG. 2 is a BET diagram of negative electrode materials according to some embodiments and comparative examples of the present disclosure.

[0033] FIG3 is a diagram showing the pore size distribution of negative electrode materials according to some embodiments and comparative examples of the present disclosure. DETAILED DESCRIPTION

[0034] The embodiments of the present disclosure are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present disclosure, but should not be understood as limiting the present disclosure.

[0035] A first embodiment of the present disclosure provides a method for preparing a graphite negative electrode material, comprising the following steps:

[0036] (1) dissolving chitosan in a solvent to obtain a chitosan solution; adding graphite and supercritical fluid exfoliated graphene to the chitosan solution and mixing them to obtain a mixture;

[0037] (2) The mixture is dried and then carbonized to obtain a graphite negative electrode material.

[0038] The method for preparing the graphite anode material of the disclosed embodiments utilizes a solution method to coat chitosan onto the surfaces of graphite and supercritical fluid-exfoliated graphene, resulting in a complete coating layer and improved overall performance of the graphite anode material. The supercritical fluid-exfoliated graphene is then bonded, coated, and carbonized by the high-temperature molten state of chitosan, forming a channel-rich anode material. This allows for the preparation of a graphite anode material with multiple lithium storage channels, enhances the conductivity of the graphite anode material, promotes lithium ion transport, and improves the rate capability and cycling performance of lithium-ion batteries.

[0039] In some embodiments, in step (1), the method for preparing supercritical fluid exfoliated graphene includes: mixing graphite and supercritical CO2, performing fluid shearing, and then discharging CO2 through pressure relief to obtain supercritical fluid exfoliated graphene.

[0040] In some embodiments, graphite is first pre-treated by ball milling to obtain graphite powder, and then the pre-treated graphite powder is added to an autoclave and supercritical CO2 is introduced for mixing.

[0041] In some embodiments, the ball milling is performed using a ball mill.

[0042] In some embodiments, the fluid shear temperature is 44-62°C, specifically, for example, 44°C, 50°C, 54°C, 60°C, 62°C.

[0043] In some embodiments, the fluid shear pressure is 8.6-11.3 MPa, specifically, for example, 8.6 MPa, 9 MPa, 9.8 MPa, 10 MPa, 11 MPa, 11.3 MPa.

[0044] In some embodiments, the fluid shearing speed is 1600-2400 r / min, specifically, for example, 1600 r / min, 2000 r / min, 2100 r / min, 2400 r / min.

[0045] In some embodiments, the fluid is sheared for 15-60 min, specifically, for example, 15 min, 30 min, 35 min, 45 min, 60 min.

[0046] In some embodiments of the present disclosure, a method for preparing supercritical fluid exfoliated graphene is adopted, and the excellent diffusivity, permeability and solubility of supercritical CO2, as well as its low viscosity and surface tension, are utilized to facilitate intercalation into the graphite interlayers; and the high-speed rotation generates a strong shear force between the CO2 fluids, which not only strengthens the diffusion process of the molecules, but also promotes the destruction of the van der Waals forces between the graphite layers by the molecules, and combined with the rapid pressure relief and expansion of supercritical CO2, the graphite is exfoliated to prepare supercritical fluid exfoliated graphene. Compared with other methods of widening the graphite interlayer spacing by introducing strong acids or strong bases to achieve the effect of rapid embedding of lithium ions into graphite, this method not only greatly reduces costs, but also does not produce a large amount of waste acid and is environmentally friendly. Compared with other graphenes, supercritical fluid exfoliated graphene is beneficial to further improve the fast charging performance, rate performance and cycle performance of negative electrode materials.

[0047] In some embodiments of the present disclosure, the graphite raw material is first pre-treated by ball milling to reduce the particle size and number of layers, facilitating supercritical exfoliation. In a supercritical state, temperature, pressure, fluid shear rate, and time significantly affect graphene. Adjusting temperature and pressure to obtain a supercritical fluid suitable for the anode material exfoliates the graphene, accelerating electron transfer and improving the rate performance of the anode material.

[0048] In some embodiments, graphite is pre-treated by ball milling to obtain graphite powder, and then the pre-treated graphite powder is added to an autoclave and packaged, and the temperature of the autoclave is set. When the temperature reaches the set value, CO2 gas is introduced, and the pressure pump is turned on. When the pressure reaches a predetermined value, the valve is closed to stop the introduction of CO2 gas, and fluid shearing is performed. Then, CO2 is discharged by pressure relief to obtain supercritical fluid exfoliated graphene.

[0049] In some embodiments, the ball milling is performed using a ball mill. In some embodiments, the fluid shearing is performed using magnetic stirring.

[0050] In some embodiments, in step (1), the graphite comprises natural flake graphite. In some embodiments, the graphite has a particle size of 70-100 μm, specifically, for example, 70 μm, 80 μm, 90 μm, or 100 μm.

[0051] In some embodiments, in step (1), the viscosity of the chitosan is 200 to 500 mPa·S, specifically, for example, 200 mPa·S, 300 mPa·S, 400 mPa·S, 500 mPa·S. In some embodiments, the particle size of the chitosan is 80 to 100 μm. In some embodiments, the solvent is a non-oxidizing acid. In some embodiments, the non-oxidizing acid includes at least one of hydrochloric acid, sulfuric acid, and citric acid. In some embodiments, the concentration of the non-oxidizing acid is 0.5 to 2 mol / l. In some embodiments, the ratio of the chitosan to the solvent is 1-3 g: 200-300 mL, specifically, for example, 1-3 g (1 g, 1.5 g, 2 g, 3 g): 200-300 mL (200 mL, 250 mL, 300 mL).

[0052] In some embodiments, in step (1), the ratio of the mass of the graphite and supercritical fluid exfoliated graphene to the mass of chitosan is 20:1-3, specifically, for example, 20:1, 20:1.5, 20:1.8, 20:2, 20:3. In some embodiments, in the graphite and supercritical fluid exfoliated graphene, the mass percentage of supercritical fluid exfoliated graphene is 0.01-10%, specifically, for example, 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%. In some embodiments of the present disclosure, the amount of graphite, supercritical fluid exfoliated graphene, and chitosan is adjusted, which is beneficial to improving the rate performance and cycle performance of the negative electrode material. When the amount of supercritical fluid-exfoliated graphene added is relatively large or the amount of chitosan used is relatively small, the material will find it difficult to form a complete carbon-coated structure due to the large specific surface area of ​​the supercritical fluid-exfoliated graphene; when the amount of supercritical fluid-exfoliated graphene added is relatively small or the amount of chitosan used is relatively large, although the coating state is good, the improvement in the conductivity of the material is not obvious.

[0053] In some embodiments, in step (2), the drying is performed by rotary evaporation. In the disclosed embodiments, the solvent is removed by rotary evaporation.

[0054] In some embodiments, in step (2), the carbonization process adopts programmed temperature rise, and the programmed temperature rise comprises: heating to 800-900°C (specifically, for example, 800°C, 850°C, 900°C) at a heating rate of 3-8°C / min (specifically, for example, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min), then heating to 1000-1200°C (specifically, for example, 1000°C, 1100°C, 1150°C, 1200°C) at a heating rate of 1-3°C / min (specifically, for example, 1°C / min, 2°C / min, 3°C / min), and keeping warm for 1-3h (specifically, for example, 1h, 2h, 3h). In some embodiments, after keeping warm, the temperature is lowered to 20-30°C, specifically, for example, 20°C, 25°C, 30°C. In some embodiments, the temperature is raised from room temperature. In some embodiments, the carbonization treatment is performed in an Ar atmosphere.

[0055] In the disclosed embodiments, the carbonization process can affect the degree of coating of the coating material. By adjusting the carbonization process, such as the carbonization temperature and time, it is beneficial to obtain an ordered coating layer, thereby affecting the wetting effect of the electrolyte on the graphite negative electrode material in the battery, affecting the rate of lithium ion embedding into the negative electrode material, and further improving the fast charging performance of the battery. If the carbonization temperature is too low, the defect degree of the carbon coating layer is relatively high, which is not conducive to improving the conductivity of the material. When the carbonization temperature is too high, the defect degree in the material is relatively low. Although the conductivity of the graphite negative electrode material is greatly improved, the lithium ion storage sites are reduced, and the lithium embedding capacity is reduced.

[0056] In some embodiments, the carbonization process further includes grinding and screening.

[0057] In some embodiments, in step (2), the particle size of the graphite negative electrode material is 10-70 μm, specifically, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm.

[0058] A second embodiment of the present disclosure provides a graphite negative electrode material, prepared using the preparation method described in any embodiment of the first embodiment of the present disclosure. In this embodiment, supercritical fluid-exfoliated graphene is composited with graphite through bonding, coating, and carbonization of molten chitosan at high temperature to construct a channel-rich negative electrode material. This enables the preparation of a graphite negative electrode material with multiple lithium storage channels, improves the conductivity of the graphite negative electrode material, promotes lithium ion transport, and enhances the rate capability and cycling performance of lithium-ion batteries.

[0059] The third embodiment of the present disclosure provides an application of the graphite negative electrode material of any embodiment of the second aspect of the present disclosure, wherein the graphite negative electrode material is used in a lithium-ion battery. In the embodiment of the present disclosure, all advantages of the graphite negative electrode material are possessed, which will not be repeated here.

[0060] A fourth embodiment of the present disclosure provides a lithium-ion battery, comprising the graphite negative electrode material described in any embodiment of the second aspect of the present disclosure. The present embodiment has all the advantages of the graphite negative electrode material, which will not be elaborated here.

[0061] The present disclosure is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present disclosure in any way.

[0062] Example 1

[0063] The preparation method of the graphite negative electrode material comprises the following steps:

[0064] (1) Graphite is pre-milled to obtain graphite powder, and then the pre-treated graphite powder is added to an autoclave, supercritical CO2 is introduced for mixing, and fluid shearing is performed, the fluid shearing temperature is 54°C, the fluid shearing pressure is 9.8 MPa, the fluid shearing speed is 2100 r / min, and the fluid shearing time is 35 min, and then the CO2 is discharged by pressure relief to obtain supercritical fluid exfoliated graphene;

[0065] (2) 1.5 g of chitosan (viscosity 300 mPa·S) was placed in 250 ml of 1 mol / l hydrochloric acid and fully dissolved to obtain a chitosan solution; 19 g of graphite and 1 g of supercritical fluid exfoliated graphene (5%) were then added thereto, and the mixture was fully stirred to obtain a mixture; the hydrochloric acid solvent in the mixture was removed by rotary evaporation, and then carbonization treatment was performed. The carbonization treatment adopted a programmed temperature increase: from room temperature to 900°C at 5°C / min, and then to 1100°C at 2°C / min, and kept warm for 2 hours to obtain a graphite negative electrode material.

[0066] Material characterization:

[0067] The graphite raw material and the graphite negative electrode material of Example 1 were characterized by SEM.

[0068] Lithium battery performance test:

[0069] 1) The negative electrode material, acetylene black and PVDF were mixed in a mass ratio of 92:3:5, an appropriate amount of NMP was added, and the mixture was stirred at room temperature for 6 hours. The mixture was coated on a copper foil, dried at 120°C for 12 hours, and pressed into a negative electrode sheet with a diameter of 13 mm using a tablet press;

[0070] 2) Assemble CR2032 button batteries in the glove box.

[0071] 3) Carry out charge and discharge tests in the Xinwei battery testing system to test the battery's rate performance and cycle performance.

[0072] Example 2

[0073] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the amount of graphite used is 19.6 g, and the amount of supercritical fluid exfoliated graphene used is 0.4 g (2%).

[0074] Example 3

[0075] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the amount of graphite used is 18.4 g, and the amount of supercritical fluid exfoliated graphene used is 1.6 g (8%).

[0076] Comparative Example 1

[0077] The performance test method is the same as that of Example 1, except that the negative electrode material uses a commercial graphite negative electrode.

[0078] Comparative Example 2

[0079] The performance test method is the same as that of Example 1, except that the negative electrode material is graphite.

[0080] Comparative Example 3

[0081] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the amount of graphite used is 20.0 g, and no supercritical fluid is added to exfoliate the graphene.

[0082] Comparative Example 4

[0083] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the supercritical fluid exfoliated graphene is replaced by commercial graphene (purchased from Pioneer Nano).

[0084] Comparative Example 5

[0085] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), supercritical exfoliated graphene is replaced by few-layer graphene.

[0086] Comparative Example 6

[0087] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the supercritical fluid exfoliated graphene is replaced by graphene oxide.

[0088] Comparative Example 7

[0089] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the supercritical fluid exfoliated graphene is replaced by hydrogenated graphene.

[0090] Comparative Example 8

[0091] The preparation method and performance test method are the same as those in Example 1, except that in step (2), no chitosan is added, that is, 19 g of graphite and 1 g of supercritical fluid exfoliated graphene (5%) are fully stirred to obtain a graphite negative electrode material.

[0092] Comparative Example 9

[0093] The preparation method and performance test method are the same as those in Example 1, except that in step (2), chitosan is replaced by asphalt, that is, 1.5 g of asphalt is placed in 250 ml of 1 mol / l hydrochloric acid and mixed thoroughly to obtain a mixed solution.

[0094] Comparative Example 10

[0095] The preparation method and performance test method are the same as those in Example 1, except that in step (2), chitosan is replaced by epoxy resin, that is, 1.5 g of epoxy resin is placed in 250 ml of 1 mol / l hydrochloric acid and mixed thoroughly to obtain a mixed solution.

[0096] Comparative Example 11

[0097] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), chitosan is replaced by glucose.

[0098] Comparative Example 12

[0099] The preparation method and performance testing method are the same as those in Example 1, except that in step (2), the carbonization temperature is 1300°C.

[0100] That is, the programmed temperature rise program is: from room temperature to 900°C at 5°C / min, then to 1300°C at 2°C / min, and keep warm for 2h.

[0101] Comparative Example 13

[0102] The preparation method and performance test method are the same as those in Example 1, except that in step (2), the temperature program is: heating from room temperature to 1100°C at 5°C / min and keeping warm for 2h.

[0103] Table 1

[0104] The conductivity data of the supercritical fluid exfoliated graphene in Example 1 and the graphene in Comparative Examples 4-7 are shown in Table 1. Among them, the conductivity of the supercritical fluid exfoliated graphene in Example 1 is 4.5×10 6 S / m, which is much higher than the electrical conductivity of other graphene.

[0105] Table 2 Rate reversible capacity (mAh / g)

[0106] As can be seen from Table 2, the introduction of supercritical fluid exfoliated graphene in Examples 1-3 makes the rate performance of the graphite negative electrode material better than that of the commercial graphite negative electrode material, graphite and the negative electrode material without the addition of supercritical fluid exfoliated graphene in Comparative Examples 1-3, indicating that supercritical fluid exfoliated graphene improves the rate performance of the graphite negative electrode material, and the performance is better than that of the commercial graphite negative electrode.

[0107] The negative electrode material with 5% graphene addition in Example 1 still has a capacity of 60.1 mAh g at a rate of 3C. -1 , far exceeding the commercial graphite negative electrode, which shows that the introduction of supercritical fluid exfoliated graphene increases the porous structure and promotes the transmission of lithium ions; in addition, the high conductivity of supercritical fluid exfoliated graphene is conducive to improving the rate performance and fast charging performance of graphite negative electrode materials. In Example 2, the addition amount of supercritical fluid exfoliated graphene is 2%, and the charge capacity is 45.9 mAh g at a 3C rate. -1 The capacity is 200W, but lower than the performance of 5% addition in Example 1. This is because when the addition amount of supercritical fluid exfoliated graphene is lower than that in Example 1, it is not conducive to fully exerting the high conductivity characteristics of supercritical fluid exfoliated graphene, resulting in relatively poor performance of the negative electrode material at high rate. When the addition amount of supercritical fluid exfoliated graphene in Example 3 is 8%, the performance at 3C rate is slightly higher than 2%, but lower than 5%. This is because although the amount of supercritical fluid exfoliated graphene is increased in Example 3, due to the relatively large addition amount of supercritical fluid exfoliated graphene, the chitosan coating is relatively incomplete, and the supercritical fluid exfoliated graphene cannot be fully and tightly attached to the graphite, which is not conducive to high conductivity, thereby affecting the high rate performance of the graphite negative electrode material.

[0108] By comparing Example 1 with Comparative Examples 4-7, it can be seen that the graphite negative electrode material using supercritical fluid to exfoliate graphene in Example 1 has a significantly improved capacity at high rate compared to negative electrode materials using other graphenes.

[0109] Comparing Example 1 with Comparative Examples 8-11, it can be seen that the graphite anode material using chitosan in Example 1 has the best rate performance compared to the other coating materials. This is due not only to the ultra-high conductivity of graphene exfoliated by supercritical fluid, but also to the unique characteristics of chitosan as a precursor. After high-temperature carbonization at 1100°C, the chitosan-coated graphite material forms a regular core-shell structure. This structure effectively reduces lithium ion diffusion resistance and greatly improves the diffusion rate of lithium ions in the electrolyte.

[0110] By comparing Example 1 with Comparative Examples 12-13, it can be seen that adjusting the temperature of the carbonization treatment and the heating process is beneficial to further improve the rate performance of the graphite negative electrode material.

[0111] Table 3 Cyclic reversible capacity (0.1C, mAh / g)

[0112] It can be seen from Table 3 that the long cycle performance of graphite negative electrode materials coated with different coating materials is different. Due to the unique structure of chitosan after carbonization treatment, the electrolyte is completely infiltrated, forming a stable SEI film on the surface of the material, which makes Example 1 have excellent long cycle performance. After 2000 cycles, the reversible capacity still reaches 329.4 mAh / g.

[0113] Figure 1 is an SEM image of the graphite in Comparative Example 2 and the graphite negative electrode material in Example 1. It can be seen from the figure that the graphite negative electrode material modified by chitosan and supercritical fluid exfoliation of graphene in Example 1 is smooth, and the graphene forms a complete coating layer.

[0114] Figures 2 and 3 are BET diagrams and pore size distribution diagrams, respectively. The specific surface area of ​​the commercial graphite negative electrode material in Comparative Example 1 is 1.04 m 2 / g, the specific surface area of ​​the graphite in Comparative Example 2 is 0.54m 2 / g, the specific surface area of ​​the graphite negative electrode material of Example 1 is 4.67m 2 / g, the specific surface area of ​​the graphite negative electrode material of Example 2 is 3.12m 2 / g, the specific surface area of ​​the graphite negative electrode material of Example 3 is 5.68m 2 / g. After the introduction of supercritical fluid to exfoliate graphene in the embodiment, the specific surface area of ​​the graphite negative electrode material increases, which increases the contact area between the material and the electrolyte, which is beneficial to the insertion and extraction of lithium ions. In addition, it can be seen from the pore size distribution diagram that the pore richness and pore volume of the graphite negative electrode material in the embodiment increase, indicating that the introduction of supercritical fluid to exfoliate graphene increases the multi-porous structure of the material, providing more abundant paths for the insertion and extraction of lithium ions, which is beneficial to fast charging performance.

[0115] In the present disclosure, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0116] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present disclosure. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present disclosure.

Claims

1. A preparation method of a graphite anode material, characterized in that, It includes the following steps: (1) Dissolve chitosan in a solvent to obtain a chitosan solution; add graphite and supercritical fluid exfoliated graphene to the chitosan solution and mix to obtain a mixture; (2) Dry the mixture and then perform carbonization treatment to obtain a graphite anode material.

2. The preparation method of the graphite anode material according to claim 1, characterized in that In the step (1), the preparation method of the supercritical fluid exfoliated graphene includes: mixing graphite and supercritical CO2, performing fluid shearing, and then discharging CO2 by pressure relief to obtain supercritical fluid exfoliated graphene.

3. The preparation method of the graphite anode material according to claim 2, wherein, The temperature of the fluid shearing is 44 - 62 °C; and / or, the pressure of the fluid shearing is 8.6 - 11.3 MPa; and / or, the speed of the fluid shearing is 1600 - 2400 r / min; and / or, the time of the fluid shearing is 15 - 60 min.

4. The preparation method of the graphite negative electrode material according to any one of claims 1 to 3, characterized in that, In the step (1), the graphite includes natural flake graphite; and / or, the particle size of the graphite is 70 - 100 μm; and / or, the viscosity of the chitosan is 200 - 500 mPa·S; and / or, the solvent is a non-oxidizing acid; and / or, the ratio of the chitosan to the solvent is 1 - 3 g : 200 - 300 mL.

5. The preparation method of the graphite anode material according to claim 4, characterized in that, The non-oxidizing acid includes at least one of hydrochloric acid, sulfuric acid, and citric acid.

6. The preparation method of the graphite anode material according to any one of claims 1 to 5, characterized in that In the step (1), the mass ratio of the graphite and the supercritical fluid exfoliated graphene to the mass of the chitosan is 20 : 1 - 3; and / or, in the graphite and the supercritical fluid exfoliated graphene, the mass percentage of the supercritical fluid exfoliated graphene is 0.01 - 10%.

7. The preparation method of the graphite anode material according to any one of claims 1 to 6, characterized in that, In the step (2), the carbonization treatment is carried out with a programmed temperature rise; the programmed temperature rise includes: Raise the temperature at a heating rate of 3 - 8 °C / min to 800 - 900 °C, and then raise the temperature at a heating rate of 1 - 3 °C / min to 1000 - 1200 °C, and keep the temperature for 1 - 3 h.

8. The preparation method of the graphite negative electrode material according to any one of claims 1 to 7, characterized in that, In the step (2), the particle size of the graphite anode material is 10 - 70 μm.

9. A graphite anode material, characterized in that, The graphite anode material is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the graphite anode material according to claim 9, characterized in that, The graphite anode material is used in a lithium-ion battery.

11. A lithium-ion battery, characterized in that, It includes the graphite anode material described in claim 9.

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