A fast-charging graphite negative electrode material, a preparation method thereof, and a lithium ion battery

Abstract

The application discloses to belong to the technical field of lithium ion battery, specifically relates to a kind of fast charging graphite negative electrode material, its preparation method and lithium ion battery, and lithium ion battery negative electrode material is graphene / carbon nanotube composite and graphdiyne modified graphite, graphene / carbon nanotube composite and graphdiyne are coated on the surface of graphite particle, and the mass percentage of graphene / carbon nanotube composite in modified graphite is 0.1-1%;The mass percentage of graphdiyne in modified graphite is 0.05-0.5%.In graphene / carbon nanotube composite, the mass ratio of graphene and carbon nanotube is 1:1~5:1.The fast charging graphite negative electrode material can effectively improve the safety performance of the battery while improving the fast charging performance.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion batteries, specifically relating to a fast-charging graphite anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries are rechargeable batteries composed of four main materials: a positive electrode, a negative electrode, a separator, and an electrolyte, along with other auxiliary materials. Graphite is currently the primary negative electrode material in commercially available lithium-ion batteries. With the rapid growth of electric vehicles in recent years, coupled with range anxiety, the new problems of "difficult and slow charging" have become increasingly prominent. Since the overall energy density of lithium-ion batteries cannot be increased indefinitely, the only way to alleviate these problems is to increase charging speed, leading to an explosive growth in demand for fast-charging graphite negative electrode materials.

[0004] Due to the sp2 hybridization of carbon atoms, graphite exhibits a layered structure. Lithium ions can only be inserted and extracted from the edges of the graphite layers, and cannot enter or exit perpendicular to the graphite layers. This is the fundamental reason affecting fast charging of graphite. Furthermore, during fast charging, electrochemical polarization increases. If lithium ions cannot diffuse into the graphite interlayer in time, they will be reduced to metallic lithium on the surface of the negative electrode. The dendritic structure of metallic lithium can easily pierce the separator, causing an internal short circuit and leading to a safety hazard. More critically, during fast charging, the high current causes the battery to heat up rapidly. This can lead to a temperature rise that fails to match the system's temperature threshold and can also cause rapid battery aging, resulting in performance degradation and increased safety risks.

[0005] The industry typically employs particle structure design and surface modification methods to achieve fast charging of graphite: for example, mixing petroleum coke / asphalt coke and asphalt, kneading, and then graphitizing at high temperature to obtain artificial graphite materials with a secondary particle structure; loading metals and / or metal compounds onto graphite, and reacting the graphite loaded with catalysts with reactive gases to obtain graphite anode materials with porous structures; or mixing graphite with modifiers, granulating, graphitizing, and coating to obtain spherical fast-charging graphite anode materials.

[0006] The inventors discovered that the above technologies, through structural modification or surface coating, only optimize the space for lithium ion insertion / extraction, but do not substantially improve the temperature rise and safety issues during fast charging. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a fast-charging graphite anode material, its preparation method and lithium-ion battery. This lithium-ion battery anode material can improve fast-charging performance and also effectively improve the safety performance of the battery.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] In a first aspect, the present invention provides a fast-charging graphite anode material, which is graphene / carbon nanotube composite and graphyne-modified graphite, wherein the graphene / carbon nanotube composite and graphyne are coated on the surface of graphite particles, and the graphene / carbon nanotube composite accounts for 0.1-1% of the modified graphite by mass; the graphyne accounts for 0.05-0.5% of the modified graphite by mass.

[0010] In the graphene / carbon nanotube composite, the mass ratio of graphene to carbon nanotubes is 1:1 to 5:1.

[0011] Secondly, the present invention provides a method for preparing the fast-charging graphite anode material, comprising the following steps:

[0012] After the graphene / carbon nanotube composite is mixed with graphite in a certain proportion, the mixed powder is mechanically fused to depolymerize the graphene / carbon nanotube composite and coat it onto the graphite substrate, thus obtaining a graphite composite powder loaded with the graphene / carbon nanotube composite.

[0013] After uniformly mixing graphite composite powder loaded with graphene / carbon nanotube composite with graphyne in a certain proportion, mechanical fusion is performed to depolymerize the graphyne and coat it onto the graphite substrate to obtain the anode material.

[0014] The mechanical fusion machine has a rotation speed of 100-1800 rpm, a tool gap width of 0.1-0.5 cm, and a fusion time of 0.5-2 h.

[0015] Thirdly, the present invention provides a lithium-ion battery, wherein the negative electrode material is the fast-charging graphite negative electrode material.

[0016] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0017] The ultra-large interlayer spacing and planar large ring structure of graphdiene can quickly and effectively provide more Li ion intercalation / deintercalation, improving fast-charging performance while reducing the risk of lithium plating. Secondly, the ultra-high conductivity of graphene / carbon nanotubes can effectively improve electron transport rate, accelerate electrochemical reaction rate, and improve fast-charging performance. Furthermore, while the ohmic impedance of a battery cell remains relatively stable during service, the electrochemical impedance gradually increases due to aging, with charge transfer impedance being particularly prominent. This leads to a gradual increase in heat generation during cyclic aging, especially during fast charging. Graphene / carbon nanotubes, due to their excellent conductivity and heat dissipation capabilities, can reduce charge transfer impedance and heat generation; on the other hand, they can quickly transfer the generated heat to the cell surface through the current collector, preventing heat accumulation, effectively reducing cell temperature rise, and improving safety performance.

[0018] Graphene sheets have a diameter of 1-10 μm, while graphyne sheets have a diameter of 10-100 nm, with the area ratio of a single graphene sheet to graphyne sheet often around 50 times. Therefore, in order to enable graphene and graphyne to exert their respective effects simultaneously, a method is adopted where graphene / carbon nanotubes and graphite are first mechanically mixed, so that a layer of graphene / carbon nanotubes is first coated on the graphite surface to improve the conductivity and heat dissipation performance of graphite. Then, graphyne is coated on the outermost layer of graphite. Due to the ultra-large interlayer spacing (0.365 nm) and the planar conjugated π-bond system composed of multiple carbon atoms of graphyne, the desolvation interface energy threshold of lithium-ion interface can be significantly reduced, and more Li-ion intercalation and deintercalation can be provided rapidly and effectively.

[0019] Compared to graphene alone, graphene / carbon nanotube composites not only improve the conductivity and heat dissipation of the negative electrode, but also enhance the mechanical properties of graphite itself and between graphite particles, thereby improving the mechanical compressive strength and cycle performance of the entire negative electrode sheet. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a SEM image of the fast-charging graphite composite powder B prepared in Example 1;

[0022] Figure 2 This is a graphene / carbon nanotube morphology diagram from Example 1;

[0023] Figure 3 This is a schematic diagram of the structure of fast-charging graphite composite powder B prepared in Example 1;

[0024] Figure 4This is a magnified view of a portion of the graphene / carbon nanotube morphology in Example 1;

[0025] Figure 5 This is a surface morphology diagram of graphdiene in Example 1;

[0026] Figure 6 This is a graph showing the charge and discharge performance of a button battery.

[0027] Figure 7 The images show the lithium intercalation curves (a) and a partial magnified view (b) of the button batteries of Example 1 and Comparative Examples 1 and 2. Detailed Implementation

[0028] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] In a first aspect, the present invention provides a fast-charging graphite anode material, which is graphene / carbon nanotube composite and graphyne-modified graphite, wherein the graphene / carbon nanotube composite and graphyne are coated on the surface of graphite particles, and the graphene / carbon nanotube composite accounts for 0.1-1% of the modified graphite by mass; the graphyne accounts for 0.05-0.5% of the modified graphite by mass.

[0030] In the graphene / carbon nanotube composite, the mass ratio of graphene to carbon nanotubes is 1:1 to 5:1.

[0031] To improve the fast-charging performance of existing graphite and address the issues of temperature rise and safety risks associated with fast-charging graphite in existing technologies, this invention coats the graphite surface with graphyne and a graphene / carbon nanotube composite. Utilizing the ultra-large interlayer spacing (0.365 nm, compared to 0.335 nm for graphite) and the large conjugated carbon bond system composed of multiple (generally more than 6, such as 18) carbon atoms, graphyne can provide Li-bearing sites both laterally and longitudinally. This significantly reduces the lithium-ion interface desolvation energy threshold, improving fast-charging performance, and also contributes to the stability of the bulk graphite layered structure.

[0032] The graphene / carbon nanotube composite in this invention is commercially sourced, and the graphene / carbon nanotube composite is a pre-mixed commercial composite powder.

[0033] Simultaneously, the highly conductive network formed by the graphene and carbon nanotube composite significantly reduces ohmic resistance and polarization resistance, minimizing heat accumulation during fast charging and improving safety performance. The fast-charging negative electrode material of this invention significantly improves fast-charging performance while effectively avoiding the risk of thermal runaway caused by fast charging, thus enhancing safety.

[0034] Carbon nanotubes are conductive modifiers for graphene, exhibiting superior conductivity compared to graphene itself, and can improve the heat dissipation performance of anode materials to a certain extent. Furthermore, carbon nanotube coating of graphite enhances the mechanical properties of graphite itself and the mechanical properties between graphite particles, thereby improving the overall mechanical compressive strength and cycle performance of the anode sheet.

[0035] If there is too much graphene, it will result in an excessively large specific surface area, causing a decrease in overall performance (including compaction density, initial charge-discharge coulombic efficiency, cycle performance, etc.); if there is too little graphene, it will result in a decrease in electrical conductivity and heat dissipation performance.

[0036] Too much graphylene will result in an excessively large specific surface area, which will also cause a decrease in overall performance (including compaction density, initial charge-discharge coulombic efficiency, cycle performance, etc.); if there is too little graphylene, the number of lithium-bearing sites will decrease, and the fast-charging performance will be reduced.

[0037] In the actual preparation, the inventors chose to first coat graphene / carbon nanotube composites onto graphite, and then coat graphyne onto the graphene / carbon nanotube-loaded graphite composite powder, ultimately obtaining graphene / carbon nanotube composites and graphyne-modified graphite. Since the graphene / carbon nanotube composite is located in the middle layer of the modified graphite, and the graphyne is located on the outermost layer, this structure allows the graphyne to be fully exposed on the outermost side of the modified graphite, effectively providing Li-bearing sites. Therefore, the most preferred embodiment of this invention is that the graphyne is exposed on the outermost side of the negative electrode material.

[0038] During the experiment, the inventors also tried a preparation method that first mixes graphyne and graphite, and then mixes and coats them with graphene / carbon nanotube composites. The product prepared by this method had poor performance. The analysis revealed that the reason was that the graphyne flakes were small in size. When it was coated on the graphite surface and then coated with large-size graphene / carbon nanotube composites, a certain amount of graphyne was trapped in the inner layer of the graphene in the graphene / carbon nanotube composite, losing its lithium-bearing site function, which in turn affected the performance of the anode material.

[0039] Furthermore, the inventors also attempted to simultaneously mix graphene / carbon nanotube composites and graphylene with graphite, followed by mechanical fusion coating. However, due to the van der Waals forces between the layers of graphene and graphylene in the graphene / carbon nanotube composite, they are prone to agglomeration not only on their own but also on each other. Therefore, to achieve separate deagglomeration and coating of graphene / carbon nanotube composites and graphylene onto the graphite particle surface, unnecessary agglomeration of graphene / carbon nanotube composites and graphylene should be avoided as much as possible, which brings great trouble to the coating process. In this case, it is also difficult to uniformly mix graphene / carbon nanotube composites and graphylene in graphite through mechanical mixing, and subsequent mechanical fusion cannot guarantee the deagglomeration and uniform coating of graphene / carbon nanotube composites and graphylene onto the graphite particles, thus affecting the performance of the anode material.

[0040] Therefore, in order to enable the graphene / carbon nanotube composite and graphyne to play their respective roles simultaneously, the graphene / carbon nanotube composite and graphite are first mechanically mixed, so that a layer of graphene / carbon nanotube composite is first coated on the graphite surface to improve the conductivity and heat dissipation performance of graphite. Then, graphyne is coated on the outermost side of the graphite. Due to the ultra-large interlayer spacing (0.365nm) and the planar conjugated π-bond system composed of multiple carbon atoms of graphyne, the desolvation interface energy threshold of lithium ion interface can be significantly reduced, and more Li ion intercalation and deintercalation can be provided quickly and effectively.

[0041] In some embodiments, the graphene / carbon nanotube composite accounts for 0.2-0.8% of the modified graphite by mass; particularly preferably 0.5%.

[0042] The graphynylene content in the modified graphite is 0.1-0.3% by mass, with a particularly preferred content of 0.25%.

[0043] In some embodiments, the D50 particle size of the graphite is 5-15 μm, preferably 10 μm.

[0044] D50 particle size is the particle size corresponding to 50% of the cumulative particle size distribution of a sample, also known as median diameter or median particle size.

[0045] In some embodiments, the graphene has a thickness of 1-10 nm and a sheet diameter of 1-10 μm; the carbon nanotubes have a diameter of 10-100 nm and a length of 100-1500 nm.

[0046] In some embodiments, the thickness of the graphdiene is 1-10 nm and the sheet diameter is 10-100 nm.

[0047] In some embodiments, the graphene / carbon nanotube composite and graphyne are embedded on a graphite substrate.

[0048] Secondly, the present invention provides a method for preparing the fast-charging graphite anode material, comprising the following steps: after mixing graphene / carbon nanotube composite with graphite in a certain proportion, mechanically fusing the mixed powder to depolymerize the graphene / carbon nanotube composite and coat it onto the graphite substrate, thereby obtaining a graphite composite powder loaded with graphene / carbon nanotube composite.

[0049] After uniformly mixing graphite composite powder loaded with graphene / carbon nanotube composite with graphyne in a certain proportion, mechanical fusion is performed to depolymerize the graphyne and coat it onto the graphite substrate to obtain the anode material.

[0050] The mechanical fusion machine has a rotation speed of 100-1800 rpm, a tool gap width of 0.1-0.5 cm, and a fusion time of 0.5-2 h.

[0051] Graphene sheets have a diameter of 1-10 μm, while graphyne sheets have a diameter of 10-100 nm. The area ratio of a single graphene sheet to graphyne sheet is often around 50 times. Figure 3 The diagram in the image exaggerates the area of ​​graphdiene to show its size; in reality, graphdiene has a much smaller area.

[0052] In some embodiments, when mixing graphene / carbon nanotube composites and / or graphylene with graphite, a V-type mixer is used, with a stirring speed of 100-500 rpm and a stirring time of 10-60 min.

[0053] In some embodiments, during mechanical fusion processing, the rotation speed of the mechanical fusion machine is 1000-1800 rpm, the tool gap width is 0.1-0.4 cm, and the fusion time is 0.5-2 h.

[0054] Graphene / carbon nanotube composites and graphyne have advantages such as large specific surface area, making them easy to aggregate. In addition, due to the addition of a small amount of graphene / carbon nanotube composites and graphyne to graphite, coupled with the aggregation effect, it is difficult to directly mix the unaggregated graphene / carbon nanotube composites and / or graphyne with graphite using conventional mixing methods.

[0055] To achieve uniform modification of graphite by graphene / carbon nanotube composites and graphyne, the inventors attempted to achieve this through a two-step mixing method. First, the aggregated graphene / carbon nanotubes were mixed with graphite, and then the graphyne was mechanically mixed with the above mixture to obtain the final composite.

[0056] Because the amount of graphene / carbon nanotube composite and graphylene added to graphite is very small, and the amount after aggregation is even smaller, it is difficult to uniformly disperse the aggregated graphene / carbon nanotube composite and graphylene in graphite.

[0057] Through repeated experiments, the inventors discovered that when using a V-type mixer with a stirring speed of 100-500 rpm and a stirring time of 10-60 min, it is possible to uniformly disperse a small amount of agglomerated graphene / carbon nanotube composite and graphylene in graphite.

[0058] When a mechanical fusion machine is used to mechanically fuse mixed powders, with a stirring speed of 100-1800 rpm and a stirring time of 0.5-2 hours, the powders, under high-speed rotation and through a narrow blade gap, utilize external mechanical force to not only depolymerize agglomerated graphene / carbon nanotube composites and graphyne, but also further disperse and uniformly embed the depolymerized graphene / carbon nanotube composites and graphyne within the graphite matrix. This method is simple, stable, and easy to scale up industrially.

[0059] This method can produce uniform materials, thus ensuring product quality.

[0060] Thirdly, the present invention provides a lithium-ion battery, wherein the negative electrode material is the fast-charging graphite negative electrode material.

[0061] The present invention will be further described below with reference to specific embodiments.

[0062] Example 1

[0063] Take 1000g of artificial graphite with a D50 of 8.5μm, and add 2g of graphene / carbon nanotubes (the morphology of which is shown in the figure). Figure 2 and Figure 3 The composite powder (as shown) was stirred and dispersed in a V-type mixer at 200 rpm for 30 min before being discharged. The graphene had an average thickness of 2 nm and an average sheet diameter of 2 μm, while the carbon nanotubes had an average diameter of 20 nm and an average length of 300 nm. The mass ratio of graphene to carbon nanotubes was 1:1.

[0064] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1200 rpm, the blade gap width was 0.3 cm, and the fusion time was 1 hour before the material was discharged, thus obtaining composite powder A of graphene and carbon nanotubes loaded on graphite.

[0065] The composite powder A was then mixed with 1g of graphdiene with an average thickness of 2.5nm and an average flake diameter of 40nm (its surface morphology is shown in the figure). Figure 5 The powder (as shown) was stirred and dispersed in a V-type mixer at a speed of 200 rpm for 30 minutes before being discharged.

[0066] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1500 rpm, the blade gap width was 0.2 cm, and the fusion time was 2 hours before discharge, thus preparing composite powder B of nanosheet graphdiyne supported on graphene / carbon nanotube modified graphite.

[0067] SEM image of the prepared composite powder B, as shown below. Figure 1 As shown.

[0068] The structural diagram of composite powder B is shown below. Figure 3 As shown.

[0069] Example 2

[0070] 1000g of artificial graphite with a D50 of 10.1μm was taken, and 4g of graphene / carbon nanotube composite powder was added. The mixture was stirred and dispersed in a V-type mixer at 300rpm for 30min before being discharged. The average graphene thickness was 2.5nm, the average sheet diameter was 2.5μm, the average carbon nanotube diameter was 20nm, the average length was 500nm, and the mass ratio of graphene to carbon nanotubes was 2:1.

[0071] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1500 rpm, the blade gap width was 0.3 cm, and the fusion time was 1.5 h before the material was discharged, thus preparing composite powder A of nanosheet graphene loaded on graphite.

[0072] The composite powder A was mixed with 2g of graphdiene with an average thickness of 2.5nm and an average flake diameter of 50nm in a V-type mixer at a speed of 300rpm and dispersed for 40min before being discharged.

[0073] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1500 rpm, the blade gap width was 0.2 cm, and the fusion time was 1.5 h before discharge. This yielded composite powder B, in which a nanosheet graphyne-based graphyne coating was loaded onto graphene / carbon nanotube modified graphite.

[0074] Example 3

[0075] 1000g of artificial graphite with a D50 of 11.5μm was taken, and 5g of graphene / carbon nanotube composite powder was added. The mixture was stirred and dispersed in a V-type mixer at 400rpm for 30min before being discharged. The graphene had an average thickness of 2.5nm and an average sheet diameter of 2.5μm, while the carbon nanotubes had an average diameter of 30nm and an average length of 800nm. The mass ratio of graphene to carbon nanotubes was 3:1.

[0076] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1200 rpm, the blade gap width was 0.3 cm, and the fusion time was 1 hour before discharge, thus preparing composite powder A of nanosheet graphene / carbon nanotubes loaded on graphite.

[0077] The composite powder A and 2.5g of graphylene powder with an average thickness of 2.5nm and an average flake diameter of 40nm were stirred and dispersed in a V-type mixer at a speed of 200rpm for 50min before being discharged.

[0078] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1500 rpm, the blade gap width was 0.2 cm, and the fusion time was 2 hours before discharge. This yielded composite powder B, in which a nanosheet graphyne-based graphyne coating was loaded onto graphene / carbon nanotube modified graphite.

[0079] Example 4

[0080] 1000g of artificial graphite with a D50 of 12.3μm was taken, and 1g of graphene / carbon nanotube composite powder was added. The mixture was stirred and dispersed in a V-type mixer at 500rpm for 40min before being discharged. The graphene had an average thickness of 3.4nm and an average sheet diameter of 5.6μm, while the carbon nanotubes had an average diameter of 50nm and an average length of 1000nm. The mass ratio of graphene to carbon nanotubes was 1:1.

[0081] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1200 rpm, the blade gap width was 0.3 cm, and the fusion time was 1 hour before discharge, thus preparing composite powder A of nanosheet graphene / carbon nanotubes loaded on graphite.

[0082] The composite powder A and 0.5g of graphylene powder with an average thickness of 6.5nm and an average flake diameter of 60nm were stirred and dispersed in a V-type mixer at a speed of 200rpm for 50min before being discharged.

[0083] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1800 rpm, the blade gap width was 0.5 cm, and the fusion time was 0.5 h before discharge. This yielded composite powder B, in which a nanosheet graphyne-based graphyne coating was loaded onto graphene / carbon nanotube modified graphite.

[0084] Example 5

[0085] 1000g of artificial graphite with a D50 of 13.6μm was taken, and 10g of graphene / carbon nanotube composite powder was added. The mixture was stirred and dispersed in a V-type mixer at 100rpm for 10min before being discharged. The graphene had an average thickness of 7.6nm and an average sheet diameter of 6.5μm, while the carbon nanotubes had an average diameter of 30nm and an average length of 1000nm. The mass ratio of graphene to carbon nanotubes was 5:1.

[0086] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 100 rpm, the blade gap width was 0.1 cm, and the fusion time was 0.5 h before discharge, thus preparing composite powder A of nanosheet graphene / carbon nanotubes loaded on graphite.

[0087] The composite powder A and 5g of graphylene powder with an average thickness of 4.3nm and an average flake diameter of 45nm were stirred and dispersed in a V-type mixer at a speed of 500rpm for 60min before being discharged.

[0088] The above materials were added to a mechanical fusion machine, the rotation speed was adjusted to 1800 rpm, the blade gap width was 0.2 cm, and the fusion time was 1 hour before discharge. This yielded composite powder B, in which a nanosheet graphyne-based graphyne coating was loaded onto graphene / carbon nanotube modified graphite.

[0089] Comparative Example 1

[0090] Take 1000g of artificial graphite with a D50 of 8.5μm, add 20g of coal-based pitch with a median particle size of 3.8μm and a softening point of 250℃, and stir and disperse in a V-type mixer at a speed of 200rpm for 30min and discharge. Then add the above material to a mechanical fusion machine, adjust the speed to 1200rpm, the blade gap width to 0.3cm, and the fusion time to 1h and discharge. Then put it into a crucible and heat treat it at 1000℃ for 4h under a nitrogen atmosphere. After cooling, the material is discharged to obtain pitch pyrolysis carbon-coated modified graphite.

[0091] Comparative Example 2

[0092] Take 1000g of artificial graphite with a D50 of 8.5μm, stir and disperse it in a V-type mixer at a speed of 200rpm for 30min, and then discharge the material. Then add the above material to a mechanical fusion machine, adjust the speed to 1200rpm, the blade gap width to 0.3cm, and the fusion time to 1h, and then discharge the material. Then put it into a crucible and heat treat it at 1000℃ for 4h under a nitrogen atmosphere. After cooling, the material is discharged to obtain pitch pyrolysis carbon-coated modified graphite.

[0093] Button battery preparation: Conductive carbon black was added to an aqueous carboxymethyl cellulose (CMC) solution, followed by the negative electrode material prepared in the examples or comparative examples. Finally, styrene-butadiene rubber (SBR) was added and stirred until homogeneous. The slurry was then evenly coated onto copper foil using a coating machine to form an electrode sheet. The coated electrode sheet was placed in a vacuum drying oven at 120°C and vacuum dried for 6 hours. The electrode sheet was then removed and rolled on a roller press for later use. Button batteries were assembled in a glove box under an argon atmosphere. The electrolyte was 1M LiPF6 + EC:DEC:DMC = 1:1:1 (volume ratio), and lithium metal sheets were used as the counter electrode. Capacity testing was performed using an Arbin BT2000 battery tester (USA), with a charge / discharge voltage range of 0.01 to 2.0V and a charge / discharge rate of 0.1C.

[0094] The button battery charge and discharge performance diagram is as follows Figure 6 As shown.

[0095] The lithium intercalation curve of a button cell is as follows: Figure 7 As shown.

[0096] Preparation of soft-pack lithium-ion batteries: The enyne graphite composite negative electrode materials prepared in each example and comparative example are dispersed in deionized water with conductive agent Super P, binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a mass ratio of 97:0.3:1.5:1.2 and stirred evenly to obtain electrode slurry.

[0097] The electrode slurry was coated onto a copper foil surface and dried at 85°C to obtain a negative electrode sheet. The negative electrode sheet was then combined with a commercially available lithium iron phosphate positive electrode, an electrolyte of 1 mol / L LiPF6 / EC+PC+DEC+EMC (volume ratio 1:0.3:1:1), and a PP / PE / PP three-layer separator with a thickness of 14 μm to fabricate a pouch cell with a capacity of approximately 3 Ah. Full-cell performance was tested within the 2.5V-3.8V range.

[0098] Table 1. Comparison of phase properties of examples and comparative examples.

[0099]

[0100] As shown in Table 1, the electronic conductivity of the composite material can be effectively improved by coating with graphene / carbon nanotubes and graphylene, which is beneficial to the performance of electrochemical properties.

[0101] Table 2 Comparison of fast charging performance of examples and comparative models

[0102]

[0103] As shown in Table 2, the ultra-large interlayer spacing and planar large ring structure of graphdiene can quickly and effectively provide more Li ion intercalation / deintercalation, improving fast-charging performance. Secondly, the ultra-high conductivity of graphene / carbon nanotubes can effectively improve electron transport rate, accelerate electrochemical reaction rate, and improve fast-charging performance. Furthermore, due to its excellent conductivity and heat dissipation functions, it can reduce charge transfer impedance and reduce heat generation. On the other hand, graphene can quickly transfer the generated heat to the cell surface through the current collector, avoiding heat accumulation, effectively reducing the temperature rise of the cell, and improving safety performance.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fast-charging graphite anode material, characterized in that: The graphene / carbon nanotube composite and graphynylene are used to modify graphite particles. The graphene / carbon nanotube composite and graphynylene are coated on the surface of the graphite particles. The mass percentage of the graphene / carbon nanotube composite in the modified graphite is 0.5%, and the mass percentage of the graphynylene is 0.25%. In the graphene / carbon nanotube composite, the mass ratio of graphene to carbon nanotubes is 1:1-5:

1. The graphene / carbon nanotube composite is located in the middle layer of the modified graphite, and the graphyne is located on the outermost side of the modified graphite. The interlayer spacing of the graphyne is 0.365 nm. Graphene has a thickness of 1-10 nm and a sheet diameter of 1-10 μm; carbon nanotubes have a diameter of 10-100 nm and a length of 100-1500 nm. The thickness of the graphdiyne is 1-10 nm, and the sheet diameter is 10-100 nm; The preparation method of the fast-charging graphite anode material includes the following steps: After the graphene / carbon nanotube composite is mixed with graphite in a certain proportion, the mixed powder is mechanically fused to depolymerize the graphene / carbon nanotube composite and coat it onto the graphite substrate, thus obtaining a graphite composite powder loaded with the graphene / carbon nanotube composite. After uniformly mixing graphite composite powder loaded with graphene / carbon nanotube composite with graphyne in a certain proportion, mechanical fusion is performed to depolymerize the graphyne and coat it onto a graphite substrate, thus obtaining the anode material.

2. The fast-charging graphite anode material according to claim 1, characterized in that: The D50 particle size of the graphite is 5-15 μm.

3. The fast-charging graphite anode material according to claim 1, characterized in that: Graphene / carbon nanotube composites and graphyne are embedded on a graphite substrate.

4. The method for preparing the fast-charging graphite anode material according to any one of claims 1-3, characterized in that: Includes the following steps: After the graphene / carbon nanotube composite is mixed with graphite in a certain proportion, the mixed powder is mechanically fused to depolymerize the graphene / carbon nanotube composite and coat it onto the graphite substrate, thus obtaining a graphite composite powder loaded with the graphene / carbon nanotube composite. After uniformly mixing graphite composite powder loaded with graphene / carbon nanotube composite with graphyne in a certain proportion, mechanical fusion is performed to depolymerize the graphyne and coat it onto the graphite substrate to obtain the anode material. The mechanical fusion machine has a rotation speed of 100-1800 rpm, a tool gap width of 0.1-0.5 cm, and a fusion time of 0.5-2 h.

5. The method for preparing the fast-charging graphite anode material according to claim 4, characterized in that: When mixing graphene / carbon nanotube composites and / or graphylene with graphite, a V-type mixer is used, with a stirring speed of 100-500 rpm and a stirring time of 10-60 min.

6. The method for preparing the fast-charging graphite anode material according to claim 4, characterized in that: During mechanical fusion machining, the mechanical fusion machine rotates at 1000-1800 rpm, the tool gap width is 0.1-0.4 cm, and the fusion time is 0.5-2 h.

7. A lithium-ion battery, characterized in that: Its negative electrode material is the fast-charging graphite negative electrode material described in any one of claims 1-3.

Images