Graphite composite material, preparation method thereof and lithium ion battery

Abstract

The application discloses a graphite composite material and a preparation method thereof and a lithium ion battery, relates to the technical field of battery preparation, and the graphite composite material comprises a core and a coating layer which at least partially coats the surface of the core; the material of the core comprises modified graphite, the modified graphite has a doping element and phosphorus element, and the doping element comprises at least one of boron element, nitrogen element and sulfur element; in the direction away from the core, the coating layer comprises a first carbon coating layer and a second carbon coating layer, and the first carbon coating layer comprises a heteroatomic element. The graphite composite material provided by the application has high lithium ion migration rate and compaction density, and thus has high kinetic performance and energy density.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a graphite composite material and its preparation method, and a lithium-ion battery. Background Technology

[0002] The market now requires not only high energy density of negative electrode active materials, but also good kinetic performance.

[0003] The main measure to improve the energy density of anode active materials is to use carbonaceous raw materials such as petroleum coke or needle coke as precursors and prepare highly crystalline artificial graphite anode materials through high-temperature graphitization treatment. However, the kinetic performance of this material will be reduced. Summary of the Invention

[0004] The main objective of this invention is to propose a graphite composite material and its preparation method, as well as a lithium-ion battery, aiming to solve the problem that existing negative electrode active materials are difficult to simultaneously possess high energy density and kinetic performance.

[0005] To achieve the above objectives, the present invention proposes a graphite composite material, which includes a core and a coating layer that at least partially covers the surface of the core.

[0006] The core material includes modified graphite, which contains doping elements and elemental phosphorus, and the doping elements include at least one of boron, nitrogen and sulfur. In the direction away from the core, the coating layer includes a first carbon coating layer and a second carbon coating layer, wherein the first carbon coating layer includes heteroatom elements.

[0007] In one embodiment, the orientation index of the graphite composite material is M, where 2 ≤ M ≤ 3.

[0008] In one embodiment, in the graphite composite material, the mass ratio of the dopant element, the heteroatom element, and the elemental phosphorus is 1~5:0.5~2:1~5; and / or, The mass of the coating layer accounts for 1 to 5 wt% of the mass of the graphite composite material.

[0009] This invention also provides a method for preparing a graphite composite material, the method comprising the following steps: S1. The calcined coke, catalyst, dopant and binder are mixed to obtain a mixture. The mixture is then subjected to pressing, first carbonization, second carbonization, graphitization and acid washing in sequence to obtain a modified graphite intermediate. S2. Phosphorus is injected into the modified graphite intermediate by ion implantation to obtain modified graphite. S3. Mix liquid tar, heteroatom compound and the modified graphite, and perform heat treatment to form a first carbon coating layer precursor on the surface of the modified graphite, to obtain an intermediate; S4. The intermediate and the coating agent are mixed and then subjected to granulation and third carbonization treatments in sequence to obtain the graphite composite material.

[0010] In one embodiment, step S3 includes: Liquid tar and heteroatom compounds are mixed and heat-treated to obtain an atomized precursor solution. The atomized precursor solution is then deposited on the surface of modified graphite by atomization to form a first carbon coating layer precursor, thus obtaining an intermediate.

[0011] In one embodiment, in step S3: The mass ratio of the liquid tar, the heteroatom compound, and the modified graphite is 2-8:1-4:100; and / or, The softening point of the liquid tar is 50-90℃; and / or, The heteroatom compound includes at least one of melamine, urea, and dopamine; and / or, The conditions for the atomization method are as follows: the atomizing carrier gas is N2 or Ar, the atomization pressure is 1.8~2.2MPa, the diameter of the guide nozzle is 0.8~1.2 mm, the deposition distance is 800~1200 mm, the atomization rate is 10-100mL / min, and the atomization time is 30-300min.

[0012] In one embodiment, in step S1: The calcined coke includes at least one of calcined petroleum coke, calcined needle coke, and calcined pitch coke; and / or The catalyst comprises at least one of iron chloride, cobalt chloride, and nickel chloride; and / or, The dopant includes at least one of hydrogen boride, ammonia, and carbon disulfide; and / or, The binder includes at least one of coal tar pitch, phenolic resin, and sucrose; and / or, The mass ratio of the calcined coke, the catalyst, the dopant, and the binder is 100:1-5:1-5:5-10; and / or, The pressure of the pressing process is 100-300 MPa; and / or, The pressing process takes 12-24 hours; and / or, The temperature of the first carbonization treatment is 500-700℃; and / or, The first carbonization treatment takes 1-3 hours; and / or, The temperature of the second carbonization treatment is 1000-1200℃; and / or, The second carbonization treatment takes 1-3 hours; and / or, The graphitization treatment is performed at a temperature of 2800-3200℃; and / or, The graphitization process takes 12-48 hours.

[0013] In one embodiment, in step S2: The mass ratio of the modified graphite intermediate to the elemental phosphorus is 100:1-5; and / or, The vacuum level during the ion implantation process of the aforementioned ion implantation method is 1.0 × 10⁻⁶. -3 Pa~5×10 -3 Pa; and / or, The radio frequency power of the ion implantation method is 100-600W; and / or, The plasma excitation method of the ion implantation method is capacitive coupling or inductive coupling, with a pulse repetition frequency of 100-500Hz and an implantation pulse width of 50-300μs; and / or, The implantation time for the ion implantation method is 30-90 min; and / or, The phosphorus element includes at least one of red phosphorus and black phosphorus; and / or, The initial vacuum level of the ion implantation method is 0.2-1.0 Pa.

[0014] In one embodiment, in step S4: The mass ratio of the modified graphite to the coating agent is 100:2-6; and / or, The coating agent includes at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt; and / or, The granulation process is carried out at a temperature of 300-500℃; and / or, The temperature of the third carbonization treatment is 1000-1300℃; and / or, The third carbonization process takes 1-6 hours.

[0015] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery comprises the aforementioned graphite composite material or the graphite composite material prepared by the aforementioned method of preparing the graphite composite material.

[0016] The present invention also provides an electrical device, the electrical device comprising the aforementioned lithium-ion battery.

[0017] In the technical solution of this invention, doping elements improve the electronic conductivity of modified graphite, elemental phosphorus improves the capacity of modified graphite, and heteroatom elements improve the electronic conductivity of the carbon coating layer. Both the first and second carbon coating layers contain amorphous carbon, which enhances the lithium-ion migration rate and the low-temperature and room-temperature performance of the graphite composite material, thereby improving its kinetic properties. Furthermore, the graphite composite material provided by this invention also has a high compaction density. In summary, the graphite composite material provided by this invention combines a high lithium-ion migration rate with a high compaction density, resulting in high kinetic performance and energy density. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a scanning electron microscope image of the graphite composite material prepared in Example 1 of the present invention.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Currently, the market not only demands high energy density from anode active materials, but also good kinetic performance. The main measure to improve the energy density of anode active materials is to use carbonaceous raw materials such as petroleum coke or needle coke as precursors, and then perform high-temperature graphitization to prepare highly crystalline artificial graphite anode materials. However, this process reduces the kinetic performance of the material.

[0023] In view of this, the present invention provides a graphite composite material comprising a core and a coating layer that at least partially covers the surface of the core; the core is made of modified graphite having a dopant element and elemental phosphorus, the dopant element comprising at least one of boron, nitrogen and sulfur; and in a direction away from the core, the coating layer comprises a first carbon coating layer and a second carbon coating layer, the first carbon coating layer comprising heteroatom elements.

[0024] In the technical solution of this invention, doping elements improve the electronic conductivity of modified graphite, elemental phosphorus improves the capacity of modified graphite, and heteroatom elements improve the electronic conductivity of the carbon coating layer. Both the first and second carbon coating layers contain amorphous carbon, which enhances the lithium-ion migration rate and the low-temperature and room-temperature performance of the graphite composite material, thereby improving its kinetic properties. Furthermore, the graphite composite material provided by this invention also has a high compaction density. In summary, the graphite composite material provided by this invention combines a high lithium-ion migration rate with a high compaction density, resulting in high kinetic performance and energy density.

[0025] The dopant element can be any one of boron, nitrogen, and sulfur, or two or three of these elements, all of which are within the scope of protection of this application. The first dopant element exists in the modified graphite through chemical bonds such as -CB-, -CN-, and -CS-.

[0026] Phosphorus can increase the specific capacity of modified graphite, and further improve the lithium-ion diffusion coefficient and compaction density of graphite composites.

[0027] The heteroatom elements in the first carbon coating layer include at least one of nitrogen, sulfur, and oxygen.

[0028] In some embodiments, the orientation index of the graphite composite material is M, where 2 ≤ M ≤ 3. The orientation index of the graphite composite material can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3. Controlling the orientation index of the graphite composite material within the range of 2 to 3 can effectively suppress the volume expansion of the graphite composite material during charge and discharge while maintaining a moderate degree of graphitization, thereby improving the migration rate and cycle stability of lithium ions.

[0029] In some embodiments, the mass ratio of the first dopant element, the heteroatom element, and the second dopant element in the graphite composite material is 1~5:0.5~2:1~5. That is, the mass ratio can be 1:0.5:5, 5:2:1, or 1:0.5:1. Controlling the mass ratio within a suitable range can ensure that the graphite composite material has good lithium-ion migration rate and compaction density.

[0030] In some embodiments, the coating layer accounts for 1 to 5 wt% of the mass of the graphite composite material. The mass percentage of the coating layer can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Within a suitable range, this mass percentage can reduce the direct contact between the modified graphite and the electrolyte, thereby suppressing the occurrence of interfacial side reactions and improving the cycle stability and safety of the material.

[0031] The present invention also provides a method for preparing a graphite composite material, the method comprising the following steps: S1, mixing calcined coke, catalyst, dopant and binder to obtain a mixture, and subjecting the mixture to pressing, first carbonization, second carbonization, graphitization and acid washing in sequence to obtain a modified graphite intermediate; injecting elemental phosphorus into the modified graphite intermediate by ion implantation to obtain modified graphite; S3, mixing liquid tar, heteroatom compound and the modified graphite, and performing heat treatment to form a first carbon coating layer precursor on the surface of the modified graphite to obtain an intermediate; S4, mixing the intermediate and coating agent, and subjecting the mixture to granulation and third carbonization in sequence to obtain the graphite composite material.

[0032] In the technical solution of this invention, in step S1, calcined coke has the characteristics of good anisotropy, fewer defects, and softer material. Graphite prepared using calcined coke as a graphite precursor material has high specific capacity and compaction density, but poor kinetics. After adding catalyst, dopant, and binder, the catalyst will change the carbon arrangement during graphitization, accelerate the graphitization rate, but promote the disordering of graphite structure, reduce the OI value (orientation index) of graphite powder, improve the isotropy of graphite, and ultimately reduce the expansion of graphite anode during electrochemical reaction and improve its kinetic performance. Dopant can provide dopant elements, thereby improving the electronic conductivity of the material. After graphitization, the binder will form amorphous carbon with high isotropy, improving the kinetic performance of the material. Acid washing can remove catalyst residues in the product to obtain modified graphite intermediate. In step S2, after obtaining the modified graphite intermediate, phosphorus is doped into the modified graphite intermediate by ion implantation to obtain modified graphite. Ion implantation has the advantages of controllable implantation process and good implantation uniformity, ensuring that phosphorus is mainly dispersed uniformly in the modified graphite intermediate in the form of elemental phosphorus. The design of the first and second carbon coating layers after phosphorus implantation avoids direct contact between phosphorus and air, preventing oxidation and combustion. Furthermore, the implantation of elemental phosphorus can improve the specific capacity and lithium-ion diffusion rate of the material, thereby improving the material's kinetic properties, as well as its compaction density and volumetric energy density. In step S3, liquid tar and heteroatom compounds are mixed with modified graphite and then heat-treated. The liquid tar and heteroatom compounds coat the surface of the modified graphite, forming a precursor for the first carbon coating layer. This precursor is carbonized during the third carbonization process to form the first carbon coating layer. The first carbon coating layer contains heteroatom elements, which can improve the material's kinetic properties. It should be noted that the composition of the atomized precursor solution in the atomization method is basically the same as that at room temperature, but it will decompose during the third carbonization process. In step S4, the intermediate is coated with a coating agent to form the second carbon coating layer precursor. During the granulation process, due to the certain viscosity of the coating agent, multiple primary graphite particles can bond together to form secondary graphite particles. Furthermore, during the carbonization process, the second carbon coating layer precursor will be transformed into amorphous carbon, thereby improving the low-temperature and room-temperature kinetic properties of the material.

[0033] It should be noted that the purpose of the pressing process in step S1 is to allow the catalyst to fully contact the calcined coke to promote the disordering of the graphite structure and reduce the OI value of the graphite powder. At the same time, pressing can increase the furnace loading and improve the preparation efficiency.

[0034] In some embodiments, step S3 includes: mixing liquid tar and heteroatom compounds and heat-treating to obtain an atomized precursor solution; depositing the atomized precursor solution on the surface of modified graphite using an atomization method to form a first carbon coating layer precursor, thereby obtaining an intermediate. The atomized precursor solution (liquid tar as solvent) formed by liquid tar and heteroatom compounds is coated onto the surface of modified graphite using an atomization method to coat the modified graphite surface with a first carbon coating layer precursor. This coating method results in a more uniform distribution of heteroatoms in the first carbon coating layer.

[0035] In some embodiments, in step S3: the softening point of the liquid tar is 50-90°C. The softening point of the liquid tar can be 50°C, 70°C, or 90°C. Tar within this softening point range has suitable fluidity and film-forming properties, allowing for sufficient atomization and the formation of a uniform and dense first coating layer precursor after deposition. This avoids excessively rapid evaporation due to a too-low softening point or uneven coating due to a too-high softening point. A softening point of 50-90°C means that the liquid tar can fully melt and atomize at 150-300°C, ultimately condensing uniformly into a film on the modified graphite surface. After the third carbonization treatment, a continuous, dense first carbon coating layer containing heteroatoms is formed, improving interfacial stability.

[0036] In some embodiments, in step S3, the heteroatom compound includes at least one of melamine, urea, dopamine, furan, thiophene, pyrrole, pyridine, and indole. That is, the heteroatom compound can be any one of melamine, urea, dopamine, furan, thiophene, pyrrole, pyridine, and indole, or two or more of these compounds, all within the scope of this invention. The doping of the above-mentioned heteroatom compounds in graphite is relatively stable and can improve the electronic conductivity of graphite.

[0037] In some embodiments, in step S3, the atomization conditions are as follows: the atomizing carrier gas is N2 or Ar, the atomization pressure is 1.8~2.2MPa, the nozzle diameter is 0.8~1.2mm, the deposition distance is 800~1200mm, the atomization rate is 10-100mL / min, and the atomization time is 30-300min. Controlling the atomization conditions within the above range ensures that the mixture of liquid tar and heteroatom compounds is fully atomized under the action of high-pressure inert carrier gas, forming micron-sized droplets with uniform particle size and stable distribution; at a suitable deposition distance, the droplets vaporize during flight, ensuring good wettability and film-forming ability when deposited on the modified graphite surface; by adjusting the atomization rate and time, the thickness of the first carbon coating layer precursor can be controlled and the surface coverage uniformity can be achieved, avoiding local accumulation or insufficient coating; the inert atmosphere (N2 / Ar) effectively prevents excessive oxidation or cracking of tar during high-temperature vaporization, ensuring the integrity of the carbon structure of the coating layer and the heteroatom doping efficiency.

[0038] In some embodiments, in step S1, the calcined coke includes at least one of calcined petroleum coke, calcined needle coke, and calcined pitch coke. That is, the calcined coke can be any one of calcined petroleum coke, calcined needle coke, and calcined pitch coke, or two or three of these three types, all within the scope of this invention. The calcined coke described above has high specific capacity and compaction density after graphitization, and also high energy density.

[0039] In some embodiments, in step S1, the catalyst comprises at least one of elemental iron, elemental cobalt, elemental nickel, iron chloride, cobalt chloride, nickel chloride, iron nitrate, cobalt nitrate, and nickel nitrate. That is, the catalyst can be any one of elemental iron, elemental cobalt, elemental nickel, iron chloride, cobalt chloride, nickel chloride, iron nitrate, cobalt nitrate, and nickel nitrate, or two or more of these elements, all within the scope of this invention. The above catalysts are all good graphitization inhibitors, capable of reducing the OI value (orientation index M) of the final material powder.

[0040] The mechanism of action of the above-mentioned elemental metal catalyst is as follows: Taking elemental iron as an example, after elemental iron is mixed with calcined coke, dopants and binders, it is uniformly dispersed in the calcined coke system. At temperatures below 1000℃, the moisture and volatiles in the dopants, binders and calcined coke continuously decompose or volatilize, forming a porous structure. At temperatures above 2000℃, iron catalyzes amorphous carbon, accelerating the formation of a highly disordered carbon layer.

[0041] The mechanism of action of the aforementioned metal compounds is similar to that of elemental metal catalysts.

[0042] In some embodiments, in step S1, the dopant includes at least one of hydrogen boride, ammonia, and carbon disulfide. That is, the dopant can be any one of hydrogen boride, ammonia, and carbon disulfide, or two or three of these three substances, all within the scope of this invention. The aforementioned dopant is used to provide a dopant element (such as boron, nitrogen, or sulfur). During the graphitization process, the dopant decomposes at high temperature, releasing active dopant atoms that embed into the graphite carbon layer structure, thereby regulating the electronic conductivity and interlayer spacing of the material.

[0043] In some embodiments, in step S1, the binder includes at least one of coal tar pitch, phenolic resin, glucose, sucrose, polyaniline, polypyrrole, and polydopamine. That is, the binder can be any one of coal tar pitch, phenolic resin, glucose, sucrose, polyaniline, polypyrrole, and polydopamine, or two or more of these substances, all within the scope of this invention. During carbonization, the above-mentioned binder can be converted into amorphous carbon or heteroatom-doped carbon, not only acting as a particle binder but also introducing defect structures and even providing additional doping elements (such as oxygen), thereby improving the kinetic properties of the material.

[0044] In some embodiments, in step S1, the mass ratio of the calcined coke, the catalyst, the dopant, and the binder is 100:1-5:1-5:5-10. This mass ratio can be 100:5:5:10, 100:3:3:7, or 100:1:1:5. Within a suitable range, this mass ratio can reduce the graphitization degree of the modified graphite and improve its kinetic properties.

[0045] In some embodiments, in step S1: the pressure of the pressing treatment is 100-300 MPa; and / or, the pressing treatment time is 12-48 h. The pressing treatment pressure can be 100 MPa, 200 MPa, or 300 MPa, and the pressing treatment time can be 12 h, 36 h, or 48 h. Controlling the pressing treatment pressure and time within the above range can ensure that the furnace loading amount of material is increased and the catalyst is in full contact with the calcined coke without damaging the structure of the calcined coke.

[0046] In some embodiments, in step S1: the temperature of the first carbonization treatment is 500-700℃; and / or, the time of the first carbonization treatment is 1-3h; and / or, the temperature of the second carbonization treatment is 1000-1200℃; and / or, the time of the second carbonization treatment is 1-3h; and / or, the temperature of the graphitization treatment is 2800-3200℃; and / or, the time of the graphitization treatment is 12-48h. The temperature of the first carbonization treatment can be 500℃, 600℃, or 700℃, and the time of the first carbonization treatment can be 1h, 2h, or 3h; the temperature of the second carbonization treatment can be 1000℃, 1100℃, or 1200℃, and the time of the second carbonization treatment can be 1h, 2h, or 3h; the temperature of the graphitization treatment can be 2800℃, 3000℃, or 3200℃, and the time of the graphitization treatment can be 12h, 36h, or 48h. The first carbonization treatment can effectively remove volatile components and impurity elements from calcined coke, catalysts, dopants, and binders, forming a preliminary carbon skeleton and preventing cracks or structural collapse during subsequent high-temperature treatment. The second carbonization treatment promotes the densification of amorphous carbon and the stabilization of heteroatom doping. At the same time, the catalyst migrates or volatilizes in the carbon skeleton, leaving pores, which inhibits the subsequent highly ordered arrangement of carbon and promotes the disordering of carbon layers. During the graphitization process, a moderately ordered graphite microcrystalline structure is obtained, which balances high electronic conductivity and low volume expansion rate, thereby improving the cycling stability and rate performance of the material.

[0047] It should be noted that the traditional phosphorus doping method involves directly mixing calcined coke with phosphides or elemental phosphorus, followed by carbonization and graphitization. Ultimately, phosphorus exists in graphite in the form of phosphorus pentoxide (i.e., a product of the reaction between phosphorus and oxygen in the air). Therefore, the doping uniformity of phosphorus in graphite is poor, phosphorus is almost not present in graphite in elemental form, the improvement in specific capacity of the product is small, and phosphorus pentoxide increases the impedance of graphite, thereby reducing energy density.

[0048] In some embodiments, in step S2, the mass ratio of the modified graphite intermediate to the elemental phosphorus is 100:1-5. This mass ratio can be 100:1-5, 100:1-5, or 100:1-5. A mass ratio within this range ensures sufficient phosphorus doping, thereby improving the lithium-ion diffusion rate and compaction density of the material; simultaneously, it avoids oxidation problems and even safety issues caused by excessive phosphorus doping.

[0049] In some embodiments, in step S2: the vacuum degree during the ion implantation process of the ion implantation method is 1.0 × 10⁻⁶. -3 Pa~5×10 -3Pa; and / or, the radio frequency power of the ion implantation method is 100-600W; and / or, the plasma excitation method of the ion implantation method is capacitive coupling or inductive coupling, the pulse repetition frequency is 100-500Hz, and the implantation pulse width is 50-300μs; and / or, the implantation time of the ion implantation method is 30-180min; and / or, the initial vacuum degree of the ion implantation method is 0.2-1.0Pa. Controlling the conditions of the ion implantation method within the above range can ensure that elemental phosphorus is uniformly and rapidly doped into the modified graphite intermediate.

[0050] In some embodiments, in step S2: the elemental phosphorus includes at least one of red phosphorus and black phosphorus. Red phosphorus is highly stable in air and not easily oxidized; black phosphorus has a layered structure and a high capacity.

[0051] In some embodiments, in step S3, the mass ratio of the liquid tar, the heteroatom compound, and the modified graphite is 2-8:1-4:100. That is, the mass ratio can be 2:4:100, 5:3:100, or 8:1:100. A mass ratio within the above range can ensure that the modified graphite is tightly coated by the first coating layer, avoiding direct contact between the modified graphite and the electrolyte.

[0052] In some embodiments, in step S4, the mass ratio of the modified graphite to the coating agent is 100:2-6. This mass ratio can be 100:6, 100:4, or 100:2. A mass ratio within this range ensures that the intermediate is fully coated by the coating agent. During granulation and carbonization, the coating agent forms a continuous and dense amorphous carbon second coating layer, suppressing side reactions between the modified graphite and the electrolyte.

[0053] In some embodiments, in step S4: the coating agent includes at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt. The softening points of these coating agents are distributed between 90 and 250°C, and their softening points can be 90°C, 180°C, 210°C, or 250°C. A softening point within this range ensures that the coating agent has suitable melt flowability during granulation and subsequent third carbonization treatment, enabling it to uniformly wet the surface of the intermediate and form a continuous, dense amorphous carbon coating layer. Asphalt with a softening point that is too low is prone to stickiness at room temperature or during the mixing stage, leading to agglomeration and uneven dispersion of the intermediate powder; while asphalt with a softening point that is too high requires a higher heat treatment temperature for the coating agent to fully melt, which not only increases energy consumption but may also cause localized uneven carbonization or coating defects. The preferred softening point of the coating agent is 180-250°C.

[0054] In some embodiments, in step S4: the granulation temperature is 300-500℃; and / or, the third carbonization temperature is 1000-1300℃; and / or, the third carbonization time is 1-6 hours. The granulation temperature can be 300℃, 400℃, or 500℃, the third carbonization time can be 1 hour, 4 hours, or 6 hours, and the third carbonization time can be 1000℃, 1200℃, or 1300℃. The granulation method is liquid-phase granulation, that is, when a coating agent is used as a binder, the powder is agglomerated through capillary force and liquid bridging, and then cured by carbonization. Controlling the granulation temperature within a suitable range can ensure that the coating agent is fully softened and flows and uniformly coats the intermediate particles, while avoiding the phenomenon that the coating agent is not firmly bonded due to excessively low temperature, or that the coating agent is prematurely decomposed, produces pores, or agglomerates due to excessively high temperature. Simultaneously controlling the temperature and time of the third carbonization process within the above range ensures that impurity elements in the coating agent can volatilize and be completely carbonized into a dense, electrically conductive amorphous carbon layer.

[0055] The present invention also provides a lithium-ion battery comprising the aforementioned graphite composite material or the graphite composite material prepared by the aforementioned method. Therefore, this lithium-ion battery possesses all the beneficial effects of the aforementioned graphite composite material or the aforementioned method for preparing the graphite composite material, which will not be elaborated upon here.

[0056] The present invention also provides an electrical device comprising the aforementioned lithium-ion battery. Therefore, this electrical device possesses all the beneficial effects of the aforementioned lithium-ion battery, which will not be elaborated further here.

[0057] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0058] Example 1 A graphite composite material is prepared by the following steps: Step S1: Mix 100g of needle-shaped calcined coke, 3g of ferric chloride (catalyst), 3g of hydrogen boroide (dopant) and 8g of coal tar pitch (binder) evenly, then press at a pressure of 200MPa for 24h, carbonize at a low temperature of 600℃ for 2h under a nitrogen protective atmosphere, then raise the temperature to 1100℃ for 2h, and finally graphitize at 3000℃ for 24h. After cooling to room temperature under a nitrogen protective atmosphere, add the obtained material to 1L of 0.1mol / L hydrochloric acid for acid washing, filter, and vacuum dry at 80℃ for 48h to obtain the modified graphite intermediate. Step S2: Add 100g of modified graphite intermediate to the vacuum chamber and use ion implantation to evacuate to 0.5Pa; then turn on the plasma generator, using 3g of red phosphorus as the injection source, and adjust the vacuum level to 3×10⁻⁶. -3 Pa, RF power of 300W, plasma excitation method of capacitive coupling, output voltage of 30kV, pulse repetition frequency of 300Hz, injection pulse width of 200μs, injection time of 90min, to obtain modified graphite. Steps S3-S4: Mix 5g of liquid tar (softening point 50℃) and 2.5g of melamine evenly and heat to generate an atomized precursor solution. Then, atomize and deposit the solution on the surface of 100g of modified graphite for 150min at an atomization rate of 50mL / min using an atomization method (atomizing carrier gas is Ar, atomization pressure is 2MPa, nozzle diameter is 1.0 mm, and deposition distance is 1000 mm) to obtain an intermediate. Then, add the intermediate to a drum furnace with 5g of petroleum asphalt (coating agent, softening point 90℃) and mix. Perform post-granulation at 400℃ for 1h. Finally, carbonize the obtained material at 1200℃ for 3h to obtain the artificial graphite composite material.

[0059] Example 2 A graphite composite material is prepared by the following steps: Step S1: Mix 100g of calcined petroleum coke, 1g of cobalt chloride, 1g of ammonia water and 1g of phenolic resin evenly, then press at a pressure of 100MPa for 12h, carbonize at a low temperature of 500℃ for 3h under a nitrogen protective atmosphere, then raise the temperature to 1000℃ for 3h, and finally graphitize at 2800℃ for 48h. After cooling to room temperature under a nitrogen protective atmosphere, add the obtained material to 1L of 0.1mol / L hydrochloric acid for acid washing, filter, and vacuum dry at 80℃ for 48h to obtain modified graphite intermediate; Step S2: Add 100g of modified graphite intermediate to the vacuum chamber, and use ion implantation to evacuate to 0.5Pa. Then turn on the plasma source, using 1g of black phosphorus as the injection source, and set the vacuum level of the vacuum chamber to 1.0×10⁻⁶. -3 Pa, RF power of 100W, plasma excitation method of inductive coupling, output voltage of 10kV, pulse repetition frequency of 100Hz, injection pulse width of 50μs, injection time of 30min, to obtain modified graphite. Steps S3-S4: Mix 2g of liquid tar (softening point 60℃) and 1g of urea evenly and heat to generate an atomized precursor solution. Then, atomize the solution on the surface of 100g of modified graphite for 300min at an atomization rate of 10mL / min using atomization method (atomizing carrier gas is N2, atomization pressure is 2MPa, nozzle diameter is 1.0 mm, and deposition distance is 1000 mm) to obtain an intermediate. Then, add the intermediate and 2g of coal tar pitch (coating agent, softening point 200℃) to a drum furnace for mixing. Perform post-granulation at 300℃ for 3h and carbonize at 1000℃ for 6h to obtain the artificial graphite composite material.

[0060] Example 3 A graphite composite material is prepared by the following steps: Step S1: Mix 100g of calcined pitch coke, 5g of nickel chloride, 5g of carbon disulfide and 10g of sucrose evenly, then press at 300MPa for 12h, carbonize at 700℃ for 1h under nitrogen protection, then carbonize at 1200℃ for 1h, and finally graphitize at 3200℃ for 12h. After cooling to room temperature under nitrogen protection, add the obtained material to 1L of 0.1mol / L hydrochloric acid for acid washing, filter, and vacuum dry at 80℃ for 48h to obtain modified graphite intermediate; Step S2: Add 100g of modified graphite intermediate to the vacuum chamber and use ion implantation to evacuate to 1.0Pa; then turn on the plasma generator, using 5g of red phosphorus as the injection source, at a vacuum degree of 5×10 -3 Pa, RF power of 600W, plasma excitation method of capacitive coupling, output voltage of 50kV, pulse repetition frequency of 500Hz, injection pulse width of 300μs, injection time of 30min, to obtain modified graphite. Steps S3-S4: Mix 8g of liquid tar (softening point 90℃) and 4g of dopamine evenly and heat to generate an atomized precursor solution. Then, atomize and deposit the solution on the surface of modified graphite for 30 minutes using an atomization method (atomizing carrier gas is N2; atomization pressure is 2MPa, nozzle diameter is 1.0mm, and deposition distance is 1000mm) at an atomization rate of 100mL / min to obtain an intermediate. Then, add the intermediate and 8g of mesophase pitch (coating agent, softening point 250℃) to a drum furnace for mixing and granulation at 500℃ for 1 hour. Finally, carbonize the obtained material at 1300℃ for 1 hour to obtain a graphite composite material.

[0061] Example 4 The difference between Example 4 and Example 1 is that: Liquid tar and melamine are coated onto the surface of modified graphite without atomization. The detailed preparation process of steps S3-S4 is as follows: 5g of liquid tar and 2.5g of melamine are mixed evenly, then 100g of modified graphite is added and mixed evenly, and then thermally melted at 150℃. Next, 5g of petroleum asphalt is added and the mixture is transferred to a drum furnace for mixing. Granulation is carried out at 400℃ for 1 hour. Finally, the resulting material is carbonized at 1200℃ for 3 hours to obtain the artificial graphite composite material. Other steps are the same as in Example 1.

[0062] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: Without performing step S2, the modified graphite intermediate prepared in step S1 is directly passed through steps S3 and S4 to obtain the graphite composite material.

[0063] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that: In step S1, ferric chloride and hydrogen borate are not added, but everything else is the same as in Example 1.

[0064] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is as follows: Step S2 is skipped. Step S1 is as follows: 100g of needle-shaped calcined coke, 3g of ferric chloride (catalyst), 3g of hydrogen boroide (dopant), 8g of coal tar pitch (binder), and 3g of red phosphorus are mixed evenly. The mixture is then pressed at 200MPa for 24 hours, carbonized at 600℃ for 2 hours under a nitrogen atmosphere, then carbonized at 1100℃ for 2 hours, and finally graphitized at 3000℃ for 24 hours. After cooling to room temperature under a nitrogen atmosphere, the resulting material is added to 1L of 0.1mol / L hydrochloric acid for acid washing, filtered, and vacuum dried at 80℃ for 48 hours to obtain the modified graphite intermediate. Other steps are the same as in Example 1.

[0065] Comparative Example 4 The difference between Comparative Example 4 and Comparative Example 2 is that: Without performing step S2, the material prepared in step S1 is directly passed through steps S3 and S4 to obtain the graphite composite material.

[0066] Performance testing (1) SEM test The graphite composite material prepared in Example 1 was tested by scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown.

[0067] Depend on Figure 1 It can be seen that the obtained graphite composite material is granular with an average particle size D50 of about 8-14 μm.

[0068] (2) Physicochemical tests The specific surface area and particle size of the above graphite composite material were tested according to the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries"; the phosphorus content of the graphite composite material was tested by EDS (energy dispersive spectroscopy); the powder diffusion coefficient of the graphite composite material was tested by GITT (giant current intermittent titration); and the OI value of the graphite composite powder material was calculated by the intensity ratio of the (004) and (110) diffraction peaks tested by XRD (X-ray diffraction). The test results are shown in Table 1.

[0069] (3) Button cell battery test The graphite composite materials obtained in Examples 1-4 and Comparative Examples 1-4 were assembled into coin cells according to the following methods: A binder, conductive agent, and solvent are added to the graphite composite material and stirred to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto a copper foil (single-sided areal density 6 mg / cm²). 2 The negative electrode sheet is prepared by drying, rolling, and cutting. The binder is LA132 binder, the conductive agent is SP conductive agent, and the solvent is double-distilled water. The weight ratio of graphite composite material, SP conductive agent (Super P conductive carbon black), LA132 binder (water-based polyacrylic acid binder), and double-distilled water is 95:1:4:220. Using lithium metal sheets as the counter electrode, polyethylene propylene (PEP) as the separator, and LiPF6 / EC+DEC (LiPF6 concentration 1.1 mol / L, EC and DEC volume ratio 1:1, EC is ethylene carbonate, and DEC is diethyl carbonate) as the electrolyte, CR2032 coin cells are assembled in an argon-filled glove box.

[0070] The fabricated button cells were installed on a Wuhan Landian CT2001A battery tester and charged and discharged at a rate of 0.1C, with a charging and discharging voltage range of 0.005 V to 2.0 V. The initial discharge capacity and initial discharge efficiency were measured. The 2C rate discharge capacity was then tested, and the rate performance (2C discharge capacity / 0.1C discharge capacity) was calculated. The test results are shown in Table 1.

[0071] Table 1. Characterization of graphite composite materials and coin cells corresponding to Examples 1-4 and Comparative Examples 1-4.

[0072] As can be seen from Table 1, the discharge specific capacity, first efficiency and diffusion coefficient of the graphite composite materials prepared in Examples 1-4 are significantly higher than those in Comparative Examples 1-4. The reason is that the high specific capacity phosphorus element is doped into the material to improve the specific capacity of the material, and the internal doping of heteroatoms improves the electronic conductivity of the material and improves the rate performance.

[0073] Comparing Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 4, it was found that the diffusion coefficient of the graphite composite material in Example 1 was significantly higher than that of the other comparative examples. This indicates that when phosphorus is injected simultaneously, a catalyst and a dopant are added, the diffusion coefficient of the graphite composite material can be increased synergistically, thereby significantly improving its kinetic performance.

[0074] Compared with Example 1, Example 4 shows that using the atomization method to prepare the first carbon coating layer precursor can further reduce the powder OI value of the final material, which is beneficial to reduce battery expansion.

[0075] (4) Soft-pack battery test The negative electrodes were prepared using the graphite composite materials prepared in Examples 1-4 and Comparative Examples 1-4, respectively, and the ternary material (LiMn) was used. 0.8 Co 0.1 Ni 0.1 A 2Ah soft-pack battery was prepared using O2 as the positive electrode, LiPF6 (solvent: EC+DEC (volume ratio 1:1), concentration 1.1 mol / L) as the electrolyte, and Celegard 2400 as the separator.

[0076] The negative electrode preparation steps are as follows: A binder, conductive agent, and solvent are added to the graphite composite material, and the mixture is stirred and mixed evenly to form a negative electrode slurry. The negative electrode slurry is then coated onto a copper foil (the single-sided areal density of the negative electrode is 9.5 mg / cm²). 2 Drying and roller pressing (compacted density 1.6 g / cm³) 3 The negative electrode sheet was prepared by cutting the material. The binder was LA136D binder, the conductive agent was SP conductive agent, and the solvent was double-distilled water. The weight ratio of the negative electrode material, SP conductive agent, LA136D binder and double-distilled water was 95:1:4:250. The compaction density of the negative electrode sheet was tested.

[0077] The positive electrode preparation steps are as follows: prepare a binder solution, then add a conductive agent and positive electrode material, stir and mix evenly to form a positive electrode slurry, and then coat the positive electrode slurry onto an aluminum foil (single-sided areal density 20 mg / cm²). 2 Drying, and roller pressing (compacted density 3.4 g / cm³) 3 The cathode material is prepared by cutting the cathode material into positive electrode sheets. The binder is PVDF (polyvinylidene fluoride), the conductive agent is SP, and the solvent is N-methylpyrrolidone. The weight ratio of the cathode material, conductive agent, binder, and solvent is 97:1:2:140.

[0078] The following tests were performed on the above-mentioned pouch batteries: a) Cyclic performance: The cycle performance of the battery was tested at a charge / discharge rate of 1 C / 1 C and a voltage range of 2.8 V-4.2 V at a temperature of 25±3℃. The test results are shown in Table 2. b) Ratio performance: The battery was charged to 4.2V at constant current rates of 1C, 2C, 3C, or 5C, and then charged to 100% SOC using constant voltage mode (0.1C to 4.2V, 3h). The constant current ratio was then calculated as constant current capacity / (constant current capacity + constant voltage capacity). The test results are shown in Table 2.

[0079] Table 2 Characterization of pouch cells corresponding to Examples 1-4 and Comparative Examples 1-4

[0080] The cycle performance and fast-charging performance of the pouch cells prepared from the graphite composite materials obtained in Table 2 were compared. As can be seen from Table 2, the cycle performance and fast-charging performance (constant current ratio) of the cells in the examples are significantly better than those in the comparative examples. This is because the materials in the examples have a lower OI value and an excellent diffusion coefficient, which improves the fast-charging performance of the materials; at the same time, the heteroatom doping of amorphous carbon in the coating layer and its high specific surface area improve the lithium-ion diffusion coefficient of the materials, thereby improving the rate capability and cycle performance.

[0081] Comparing Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 4, it was found that the maximum compaction density of the electrode in the pouch cell corresponding to Example 1 was significantly higher than that of the other comparative examples. This indicates that when phosphorus is injected simultaneously and catalysts and dopants are added, the maximum compaction density of the electrode in the prepared pouch cell will be significantly higher than that of the other comparative examples, thereby significantly improving its energy density.

[0082] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present 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 patent protection scope of the present invention.

Claims

1. A graphite composite material, characterized in that, The graphite composite material includes a core and a coating layer that at least partially covers the surface of the core; The core material includes modified graphite, which contains doping elements and elemental phosphorus, and the doping elements include at least one of boron and sulfur. In the direction away from the core, the coating layer includes a first carbon coating layer and a second carbon coating layer, wherein the first carbon coating layer includes heteroatom elements; The preparation method of the graphite composite material includes the following steps: S1. The calcined coke, catalyst, dopant and binder are mixed to obtain a mixture. The mixture is then subjected to pressing, first carbonization, second carbonization, graphitization and acid washing in sequence to obtain a modified graphite intermediate. S2. Phosphorus is injected into the modified graphite intermediate by ion implantation to obtain modified graphite. S3. Liquid tar and heteroatom compounds are mixed and heat-treated to obtain an atomized precursor solution. The atomized precursor solution is deposited on the surface of the modified graphite by atomization to form a first carbon coating layer precursor, thus obtaining an intermediate. S4. The intermediate and the coating agent are mixed and then subjected to granulation and third carbonization treatments in sequence to obtain the graphite composite material. The catalyst includes at least one of iron chloride, cobalt chloride, and nickel chloride; The dopant includes at least one of hydrogen boride and carbon disulfide; The binder includes at least one of coal tar pitch, phenolic resin, and sucrose. The heteroatom compound includes at least one of melamine, urea, and dopamine; The coating agent includes at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt. The conditions for the atomization method are as follows: the atomizing carrier gas is N2 or Ar, the atomization pressure is 1.8~2.2MPa, the diameter of the guide nozzle is 0.8~1.2 mm, the deposition distance is 800~1200 mm, the atomization rate is 10-100mL / min, and the atomization time is 30-300min.

2. The graphite composite material as described in claim 1, characterized in that, The orientation index of the graphite composite material is M, where 2 ≤ M ≤ 3.

3. The graphite composite material as described in claim 1, characterized in that, In the graphite composite material, the mass ratio of the dopant element, the heteroatom element, and the elemental phosphorus is 1~5:0.5~2:1~5; and / or, The mass of the coating layer accounts for 1 to 5 wt% of the mass of the graphite composite material.

4. A method for preparing a graphite composite material as described in any one of claims 1 to 3, characterized in that, The preparation method of the graphite composite material includes the following steps: S1. The calcined coke, catalyst, dopant and binder are mixed to obtain a mixture. The mixture is then subjected to pressing, first carbonization, second carbonization, graphitization and acid washing in sequence to obtain a modified graphite intermediate. S2. Phosphorus is injected into the modified graphite intermediate by ion implantation to obtain modified graphite. S3. Liquid tar and heteroatom compounds are mixed and heat-treated to obtain an atomized precursor solution. The atomized precursor solution is deposited on the surface of the modified graphite by atomization to form a first carbon coating layer precursor, thus obtaining an intermediate. S4. The intermediate and the coating agent are mixed and then subjected to granulation and third carbonization treatments in sequence to obtain the graphite composite material. The catalyst includes at least one of iron chloride, cobalt chloride, and nickel chloride; The dopant includes at least one of hydrogen boride and carbon disulfide; The binder includes at least one of coal tar pitch, phenolic resin, and sucrose. The heteroatom compound includes at least one of melamine, urea, and dopamine; The coating agent includes at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt. The conditions for the atomization method are as follows: the atomizing carrier gas is N2 or Ar, the atomization pressure is 1.8~2.2MPa, the diameter of the guide nozzle is 0.8~1.2 mm, the deposition distance is 800~1200 mm, the atomization rate is 10-100mL / min, and the atomization time is 30-300min.

5. The method for preparing the graphite composite material as described in claim 4, characterized in that, In step S3: The mass ratio of the liquid tar, the heteroatom compound, and the modified graphite is 2-8:1-4:100; and / or, The softening point of the liquid tar is 50-90℃.

6. The method for preparing the graphite composite material as described in claim 4, characterized in that, In step S1: The calcined coke includes at least one of calcined petroleum coke, calcined needle coke, and calcined pitch coke; and / or The mass ratio of the calcined coke, the catalyst, the dopant, and the binder is 100:1-5:1-5:5-10; and / or, The pressure of the pressing process is 100-300 MPa; and / or, The pressing process takes 12-24 hours; and / or, The temperature of the first carbonization treatment is 500-700℃; and / or, The first carbonization treatment takes 1-3 hours; and / or, The temperature of the second carbonization treatment is 1000-1200℃; and / or, The second carbonization treatment takes 1-3 hours; and / or, The graphitization treatment is performed at a temperature of 2800-3200℃; and / or, The graphitization process takes 12-48 hours.

7. The method for preparing the graphite composite material as described in claim 4, characterized in that, In step S2: The mass ratio of the modified graphite intermediate to the elemental phosphorus is 100:1-5; and / or, The vacuum level during the ion implantation process of the aforementioned ion implantation method is 1.0 × 10⁻⁶. -3 Pa~5×10 -3 Pa; and / or, The radio frequency power of the ion implantation method is 100-600W; and / or, The plasma excitation method of the ion implantation method is capacitive coupling or inductive coupling, with a pulse repetition frequency of 100-500Hz and an implantation pulse width of 50-300μs; and / or, The implantation time for the ion implantation method is 30-90 min; and / or, The phosphorus element includes at least one of red phosphorus and black phosphorus; and / or, The initial vacuum level of the ion implantation method is 0.2-1.0 Pa.

8. The method for preparing the graphite composite material as described in claim 4, characterized in that, In step S4: The mass ratio of the modified graphite to the coating agent is 100:2-6; and / or, The granulation process is carried out at a temperature of 300-500℃; and / or, The temperature of the third carbonization treatment is 1000-1300℃; and / or, The third carbonization process takes 1-6 hours.

9. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a graphite composite material prepared by any one of the methods described in claims 1 to 3 or as described in any one of claims 4 to 8.

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