Catalytic assisted graphitization method of a graphite material for a lithium battery negative electrode

Abstract

This invention discloses a catalytically assisted graphitization method for graphite materials used in lithium-ion battery anodes, belonging to the field of lithium-ion battery technology. Spherical mesophase carbon microspheres are mixed with ferric nitrate nonahydrate and ammonium molybdate in liquid phase and then spray-dried to obtain composite microsphere powder loaded with an iron-molybdenum catalyst precursor. This powder is then heated and mixed with medium-temperature coal tar pitch and cold isostatically pressed to obtain a composite green body. After gradient carbonization treatment, an isotropic stress field is established within the body using the shrinkage of the pitch carbonization. High-temperature catalytic graphitization is then performed at 2600℃-2800℃, causing the iron-molybdenum to form a eutectic catalytic system. This system, in conjunction with the stress field, induces carbon atom rearrangement, forming a highly crystalline graphite structure with a high degree of surface graphitization and an isotropic interwoven internal structure. Finally, the graphite is obtained through dissociation, pulverization, and classification. This invention achieves a balance between high capacity and high rate performance of the anode material through the synergistic effect of catalysis and the stress field.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a catalytic-assisted graphitization method for graphite materials used in lithium battery anodes. Background Technology

[0002] With the increasing demands for driving range and charging speed in the new energy vehicle industry, developing high-energy-density lithium-ion batteries that support fast charging has become a core direction for industry development. As a key component of lithium-ion batteries, the performance of the anode material directly determines the overall performance of the battery. Currently, artificial graphite has become the mainstream choice for power battery anode materials due to its good cycle stability and low cost.

[0003] However, traditional artificial graphite anode materials face two mutually restrictive technical bottlenecks: first, the improvement in specific capacity has reached a bottleneck, with little breakthrough after approaching the theoretical value of 372 mAh / g; second, rate performance, i.e., fast charging capability, is insufficient. This is mainly because the anisotropy of graphite crystals leads to a slow diffusion rate of lithium ions between graphite layers, and although the highly crystalline graphite structure has high capacity, it is not conducive to the rapid insertion and extraction of lithium ions, especially during high-current charging, which easily leads to lithium plating on the surface of the graphite anode, causing safety issues.

[0004] To overcome this bottleneck, catalytic graphitization technology has been extensively studied. Existing technologies, by adding transition metal catalysts such as iron and nickel to carbonaceous precursors, can promote the conversion of amorphous carbon into graphite crystals at lower temperatures, thereby improving the graphitization degree and capacity of the material. For example, patent application CN103855369A discloses a method for preparing anode materials by mixing carbon powder with a catalyst, followed by pressing, carbonization, and graphitization. However, this method has significant drawbacks: the catalyst easily escapes from the powder in gaseous form at high temperatures, resulting in uneven and low catalytic efficiency, and limited improvement in the graphitization degree of the final product. More importantly, existing technologies that simply pursue high graphitization often lead to excessively strong orientation of the resulting graphite materials, resulting in tortuous lithium-ion diffusion paths. Although the capacity is improved, the rate performance decreases, failing to simultaneously meet the requirements of high energy density and high power density. Some studies have attempted to improve rate performance through pore formation, but the disordered pore structure disrupts the integrity of the graphite structure, leading to an increase in irreversible capacity and a decrease in the first coulombic efficiency. Therefore, how to improve the capacity of materials and simultaneously optimize their rate performance through catalytic graphitization remains a technical challenge that urgently needs to be addressed in this field. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a catalytically assisted graphitization method for graphite materials used in lithium battery anodes, comprising the following steps: Step 1: Spherical mesophase carbon microsphere powder is mixed with ferric nitrate nonahydrate and ammonium molybdate in the liquid phase and then spray-dried to obtain composite microsphere powder loaded with iron-molybdenum bimetallic catalyst precursor; Step 2: The composite microsphere powder is heated and mixed with medium-temperature coal tar pitch to coat the surface of the composite microsphere powder with the molten medium-temperature coal tar pitch to form a paste mixture. The paste mixture is then cold isostatically pressed to obtain a dense composite green block. Step 3: The composite green block is subjected to gradient heating carbonization treatment under an inert atmosphere. The volume shrinkage during the medium-temperature coal tar pitch carbonization process is used to apply isotropic mechanical stress to the internal composite microsphere powder to obtain a carbonized block. Step 4: The carbonized block is subjected to high-temperature catalytic graphitization treatment under an argon atmosphere, so that the iron-molybdenum bimetallic catalyst precursor forms an iron-molybdenum carbide eutectic catalytic system that induces carbon atom rearrangement under the combined action of mechanical stress, forming a highly crystalline graphite structure with high surface graphitization and isotropic interwoven interior, thus obtaining a graphitized block. Step 5: The graphitized bulk material is mechanically crushed, air-jet pulverized and graded to collect powder within the target particle size range, which is the final graphite material for lithium battery anodes.

[0006] Preferably, the particle size range of the spherical mesophase carbon microsphere powder in step 1 is 2 micrometers to 5 micrometers; the amount of ferric nitrate nonahydrate added is calculated as 3% to 5% of the mass of iron element in the spherical mesophase carbon microsphere powder; the amount of ammonium molybdate added is calculated as 0.5% to 1.5% of the mass of molybdenum element in the spherical mesophase carbon microsphere powder; the liquid phase mixing process is as follows: firstly, the spherical mesophase carbon microsphere powder is dispersed in deionized water to form a suspension with a solid content of 25% to 35%; then, the ferric nitrate nonahydrate and the ammonium molybdate are dissolved in the suspension respectively, and stirred continuously for 4 to 6 hours at a water bath temperature of 60 degrees Celsius to 80 degrees Celsius, so that iron ions and molybdate ions are fully adsorbed and penetrated into the surface and internal pores of the spherical mesophase carbon microsphere powder; the inlet temperature of the spray drying is 210 degrees Celsius to 230 degrees Celsius, and the outlet temperature is 90 degrees Celsius to 100 degrees Celsius.

[0007] Preferably, in step 2, the mass ratio of the composite microsphere powder to the medium-temperature coal tar pitch is 100:15 to 100:20; the heating and mixing temperature is 150 degrees Celsius to 180 degrees Celsius, and the mixing time is 30 minutes to 60 minutes; the cold isostatic pressing pressure is 200 MPa to 250 MPa, and the holding time is 10 minutes to 15 minutes.

[0008] Preferably, the gradient heating carbonization treatment in step 3 specifically includes: first, heating from room temperature to 350 to 400 degrees Celsius at a heating rate of 0.5 to 1 degree Celsius per minute, and holding at that temperature for 120 to 180 minutes, so that the coated medium-temperature coal tar pitch undergoes slow melting, cross-linking, and preliminary carbonization to form a semi-coke-like outer shell; then, heating at a heating rate of 2 to 3 degrees Celsius per minute to 1000 to 1100 degrees Celsius, and holding at that temperature for 180 to 240 minutes, so that the composite microsphere powder and the semi-coke-like outer shell are completely carbonized.

[0009] Preferably, the heating rate of the high-temperature catalytic graphitization treatment in step 4 is 5°C / min to 8°C / min, the maximum temperature is 2600°C to 2800°C, and the holding time is 120 minutes to 180 minutes. During the high-temperature catalytic graphitization treatment, the ferric nitrate nonahydrate and ammonium molybdate introduced in step 1 are first reduced by carbon to elemental iron and molybdenum carbide in the carbonized block, thereby forming the iron-molybdenum carbide eutectic catalytic system. The molybdenum carbide plays a pinning role inside the carbonized block, restricting the excessive growth and single orientation of graphite microcrystals.

[0010] Preferably, the mechanical crushing in step 5 involves crushing the graphitized block into particles with a diameter of less than 5 mm; the airflow pulverization is performed under the conditions of a pulverizing pressure of 0.6 MPa to 0.8 MPa and a classifying wheel speed of 2500 rpm to 3500 rpm for fine pulverization and spheroidization; the classification process is performed by precise classification using an ultrasonic vibrating screen, and the collected target particle size range is 10 micrometers to 18 micrometers.

[0011] Preferably, the spherical mesophase carbon microsphere powder in step 1 has an isotropic structure and a D50 particle size of 2.5 micrometers to 3.5 micrometers; the softening point of the medium-temperature coal tar pitch in step 2 is 80 degrees Celsius to 90 degrees Celsius, and the quinoline insoluble content is less than 5%.

[0012] Preferably, the mold used in the cold isostatic pressing in step 2 is a rubber mold, and the paste mixture is first subjected to vacuum degassing treatment before being filled into the rubber mold. The degassing time is 10 to 20 minutes, and the degassing vacuum degree is less than 50 Pa.

[0013] Preferably, the gas flow rates of the inert atmosphere and the argon atmosphere in steps 3 and 4 are independently controlled between 5 liters / minute and 15 liters / minute to ensure that the pressure inside the furnace is in a slightly positive pressure state, with a pressure range of 100 Pa to 300 Pa.

[0014] Preferably, in step 5, the particles after mechanical crushing are subjected to magnetic separation to remove iron impurities introduced during the crushing process before the airflow pulverization. The magnetic field strength of the magnetic separation is 8000 Gauss to 12000 Gauss.

[0015] The beneficial effects of this invention are: 1. This invention utilizes an isotropic stress field constructed through iron-molybdenum bimetallic catalysis and asphalt coating-isostatic pressing to form an in-situ iron-molybdenum carbide eutectic catalytic system during graphitization. This system not only efficiently catalyzes carbon atom rearrangement to increase graphitization degree, but more importantly, the pinning effect of molybdenum carbide restricts the single-orientation growth of graphite crystallites, working in conjunction with the stress field to form a "core-shell" structure with highly crystalline surface and isotropic interweaving internally. This structure ensures high reversible capacity due to high graphitization degree while significantly improving rate performance through isotropic internal lithium-ion diffusion channels, fundamentally resolving the technical contradiction of high capacity and fast charging being mutually exclusive.

[0016] 2. This invention employs a liquid-phase adsorption combined with spray drying method to uniformly load iron and molybdenum catalyst precursors in ionic form within the nanopores of spherical mesophase carbon microspheres. Subsequent asphalt fusion coating and cold isostatic pressing processes "encapsulate" the catalyst precursors within a dense bulk, effectively suppressing catalyst aggregation and escape during the high-temperature graphitization stage. This "micro-encapsulation" effect ensures that the iron-molybdenum carbide eutectic catalytic system functions uniformly and efficiently throughout the entire bulk, resulting in significantly better uniformity of bulk graphitization in the final material compared to traditional powder catalytic processes.

[0017] 3. This invention utilizes a carbonized outer shell formed by asphalt fusion coating, which transforms into a complete and dense graphite layer after high-temperature graphitization, effectively repairing surface defects that may occur during the dissociation of internal particles. This complete surface structure significantly reduces irreversible electrolyte decomposition, increasing the initial coulombic efficiency to over 94%. Simultaneously, the isotropic internal interwoven structure uniformly buffers volume expansion and contraction during charge and discharge, effectively suppressing particle micronization. This allows the material to maintain structural integrity even after long-term cycling, demonstrating excellent cycle stability and promising commercial application prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the steps of the method of the present invention; Figure 2This is a schematic diagram showing the evolution of the microstructure of the composite microsphere powder at each process stage. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0021] Please see Figures 1-2 This invention provides a catalytically assisted graphitization method for graphite materials used in lithium-ion battery anodes. By combining iron-molybdenum bimetallic catalysis with stress field construction, the growth process of graphite microcrystals is precisely controlled, ultimately producing a high-performance graphite anode material with high surface graphitization and an isotropic interwoven internal structure. The method comprises five core steps: First, preparing composite microsphere powder loaded with an iron-molybdenum bimetallic catalyst precursor; second, mixing the composite microsphere powder with medium-temperature coal tar pitch and pressing it into a composite green body; third, establishing an isotropic mechanical stress field within the green body through gradient carbonization; fourth, performing catalytic graphitization at high temperature, utilizing the synergistic effect of the catalyst and stress field to form a unique microstructure; and finally, dissociating, pulverizing, and classifying the graphitized green body to obtain the target product. Each step is described in detail below.

[0022] Step 1: Preparation and Pretreatment of Composite Catalyst The purpose of this step is to uniformly load iron and molybdenum catalyst precursors in ionic form onto the surface and internal pores of the carbonaceous precursor—spherical mesophase carbon microsphere powder—laying the foundation for subsequent efficient and uniform catalytic action.

[0023] The carbonaceous precursor used is spherical mesophase carbon microsphere powder. This powder has an isotropic microstructure, with a preferred particle size range of 2 to 5 micrometers. In one specific embodiment, the D50 particle size of the powder is 2.5 to 3.5 micrometers. This spherical and isotropic structure helps to form a uniform stress field during subsequent molding and heat treatment.

[0024] First, the weighed spherical mesophase carbon microsphere powder is dispersed in deionized water to form a suspension with a solid content of 25% to 35%. For example, 1000 grams of spherical mesophase carbon microsphere powder can be added to 2300 grams of deionized water and stirred to form a uniform suspension with a solid content of approximately 30.3%.

[0025] Then, two catalyst precursors, ferric nitrate nonahydrate and ammonium molybdate, are added to the suspension. The amount of ferric nitrate nonahydrate added is calculated as 3% to 5% of the mass of iron in the spherical mesophase carbon microsphere powder. The amount of ammonium molybdate added is calculated as 0.5% to 1.5% of the mass of molybdenum in the spherical mesophase carbon microsphere powder. In a preferred embodiment, the iron content is 4% and the molybdenum content is 1.0%. The specific calculation method is as follows: the required mass of iron is equal to the mass of the spherical mesophase carbon microsphere powder multiplied by the target value of the iron mass fraction, and then the required mass of ferric nitrate nonahydrate is calculated based on the mass fraction of iron in ferric nitrate nonahydrate (approximately 13.86%); similarly, the required mass of ammonium molybdate is calculated based on the mass fraction of molybdenum in ammonium molybdate (approximately 54.3%).

[0026] Weigh out the ferric nitrate nonahydrate and ammonium molybdate, and add them sequentially to the suspension. Start heating and stirring. Maintain the temperature of the mixture between 60°C and 80°C, for example, 70°C, and continue stirring at this temperature for 4 to 6 hours, for example, 5 hours. The purpose of stirring is to allow the iron and molybdate ions to fully dissolve and diffuse, entering the surface and internal pores of the spherical mesophase carbon microsphere powder through adsorption and permeation, achieving uniform loading at the molecular level.

[0027] After adsorption, the mixture is spray-dried. The inlet temperature of the spray dryer is controlled between 210°C and 230°C, for example, 220°C; the outlet temperature is controlled between 90°C and 100°C, for example, 95°C. A centrifugal atomizing disc can be used for atomization, and the disc rotation speed can be adjusted according to the equipment, typically between 15,000 rpm and 20,000 rpm. In the high-temperature airflow, the droplets are instantly dried, yielding composite microsphere powder loaded with the iron-molybdenum bimetallic catalyst precursor. This powder largely retains its original spherical morphology, and the catalyst precursor is uniformly distributed without surface enrichment.

[0028] Step 2: Asphalt Fusion Coating and Block Forming The purpose of this step is to construct a dense green body from catalyst-loaded composite microsphere powder through asphalt coating and isostatic pressing, providing a structural basis for the establishment of the stress field and in-situ encapsulation of the catalyst during the subsequent carbonization process.

[0029] All the composite microsphere powder obtained in step 1 is added to a mixer and heated and mixed with medium-temperature coal tar pitch in a certain proportion. The mass ratio of composite microsphere powder to medium-temperature coal tar pitch is 100:15 to 100:20, for example, 100:15.3 or 100:20. The softening point of the medium-temperature coal tar pitch is preferably 80 to 90 degrees Celsius, and the quinoline insoluble content is less than 5%. This pitch has good fluidity and adhesion when heated.

[0030] The mixing equipment can be a Z-type kneader or similar mixing equipment with heating and strong shearing functions. The mixing temperature is set to 150°C to 180°C, for example, 160°C. At this temperature, the medium-temperature coal tar pitch melts into a highly fluid liquid phase. The mixing time is 30 to 60 minutes, for example, 45 minutes. During the continuous heating and mixing process, the molten medium-temperature coal tar pitch spreads evenly and coats the surface of each composite microsphere powder, ultimately forming a fluid paste-like mixture.

[0031] To ensure the density of the final block and avoid internal porosity defects, it is recommended to perform vacuum degassing on the paste mixture before filling the mold. The degassing time can be 10 to 20 minutes, for example, 15 minutes; the degassing vacuum level should be below 100 Pa, for example, below 50 Pa. Degassing effectively removes air bubbles trapped during the mixing process.

[0032] After degassing, the paste mixture is filled into a suitable mold, such as a rubber mold. Slight vibration should be applied during filling to ensure uniform material distribution. The sealed mold is then placed in a cold isostatic press for cold isostatic pressing. The molding pressure is controlled at 200 MPa to 250 MPa, for example, 220 MPa; this pressure is held for 10 to 15 minutes, for example, 12 minutes. Under ultra-high hydrostatic pressure, the asphalt-coated composite microsphere powder particles undergo rearrangement and plastic deformation, minimizing interparticle gaps and ultimately yielding a highly dense, defect-free cylindrical composite green body.

[0033] Step 3: Gradient carbonization treatment The purpose of this step is to induce a carbonization transformation in the coated asphalt through a precisely controlled heating process, and to utilize the volume shrinkage during carbonization to generate an isotropic mechanical stress field within the block. Simultaneously, this step also decomposes the catalyst precursor and uniformly embeds it within the carbon skeleton.

[0034] The cylindrical composite green body obtained in step 2 is placed in an atmosphere-protected carbonization furnace. First, atmosphere replacement is performed by introducing an inert atmosphere (such as nitrogen) to purge air from the furnace and ensure that the oxygen concentration is below a safe threshold (e.g., volume concentration below 10 parts per million). Then, the inert atmosphere is maintained, with the gas flow rate controlled between 5 liters / minute and 15 liters / minute, for example, 10 liters / minute, and the furnace is kept under a slightly positive pressure, ranging from 100 Pa to 300 Pa, for example, 200 Pa.

[0035] The heating program is initiated to perform gradient heating carbonization. This gradient heating process consists of two stages: The first stage involves slowly heating from room temperature to 350 to 400 degrees Celsius at a rate of 0.5 to 1 degree Celsius per minute, for example, to 380 degrees Celsius at 0.8 degrees Celsius per minute. After reaching the target temperature, hold for 120 to 180 minutes, for example, 150 minutes. The purpose of this stage is to allow the coated medium-temperature coal tar pitch to undergo a slow melting, cross-linking, and preliminary carbonization reaction, forming a semi-coke-like outer shell with a certain strength. During this process, due to the significant volume shrinkage associated with pitch carbonization, this shell applies a uniform, isotropic compressive stress to the internal composite microsphere powder. The establishment of this stress field is crucial for the final formation of an isotropic graphite structure.

[0036] The second stage involves further heating to 1000-1100 degrees Celsius at a rate of 2-3 degrees Celsius per minute, for example, to 1050 degrees Celsius at a rate of 2.5 degrees Celsius per minute. After reaching the target temperature, the temperature is held for 180-240 minutes, for example, 210 minutes. During this stage, both the composite microsphere powder itself and the semi-coke-like outer shell covering its surface undergo deep carbonization, releasing small molecule gases. The carbon skeleton further condenses, ultimately forming a fully carbonized block with a certain mechanical strength. Simultaneously, the ferric nitrate nonahydrate and ammonium molybdate loaded in the microsphere pores decompose at high temperature, transforming into nano-sized iron oxide and molybdenum oxide particles, which are uniformly embedded in the carbon skeleton of the carbonized block. After the holding period, the furnace is allowed to cool naturally to room temperature, and the carbonized block is then removed.

[0037] Step 4: High-temperature catalytic graphitization treatment This step is the core of the invention. By utilizing the synergistic effect of the iron-molybdenum bimetallic catalyst and the stress field established in step 3 at ultra-high temperature, the growth and microstructure of graphite microcrystals are precisely controlled, forming a unique structure with highly crystalline surface and isotropic interwoven interior.

[0038] The carbonized block obtained in step 3 is placed in a graphitization furnace, such as an Atchison-type graphitization furnace. After sealing the furnace, the atmosphere inside the furnace is purged with argon gas to ensure that oxygen is completely removed. Then, an argon atmosphere is maintained at a gas flow rate of 5 to 15 liters per minute, for example, 8 liters per minute, and a slight positive pressure is maintained inside the furnace, ranging from 100 Pa to 300 Pa, for example, 150 Pa.

[0039] Start the heating program and raise the furnace temperature to 2600°C to 2800°C at a rate of 5°C to 8°C per minute, for example, to 2700°C at 6°C per minute. After reaching the target temperature, hold for 120 to 180 minutes, for example, 150 minutes.

[0040] A series of complex physicochemical changes occur during the heating and holding processes. As the temperature rises, the nanoscale iron oxide and molybdenum oxide formed in step 3 are reduced by carbon. First, the iron oxide is reduced to elemental iron; the molybdenum oxide is then reduced and further reacts with carbon to form molybdenum carbide. When the temperature reaches approximately 1300 degrees Celsius or higher, the generated elemental iron and molybdenum carbide together form an iron-molybdenum carbide eutectic catalytic system. This eutectic system is liquid and possesses extremely high catalytic activity, capable of dissolving surrounding carbon atoms and, driven by a temperature or concentration gradient, promoting the re-precipitation of carbon atoms in the form of graphite crystals.

[0041] In this process, two key factors work together to determine the final graphite microstructure: First, the isotropic mechanical stress field formed during carbonization in step 3 still exists within the bulk. This stress field provides energy guidance for the rearrangement of carbon atoms and the growth of graphite crystallites, causing the C-axis of the graphite crystallites to preferentially align along the stress direction. Since the stress is isotropic, this preferential orientation exists in all directions, thus laying the foundation for the formation of isotropic structures.

[0042] Secondly, the in-situ generated molybdenum carbide particles possess extremely high melting points (approximately 2600 degrees Celsius) and chemical stability. In the liquid iron-molybdenum carbide eutectic system, they act as heterogeneous nucleation sites and pinning points. The molybdenum carbide particles pin to the grain boundaries of the growing graphite crystallites, effectively limiting excessive growth and unidirectional growth along a specific direction.

[0043] By holding the material at a high temperature of 2600°C to 2800°C for an extended period, a unique microstructure was formed through the long-term synergistic effect of the iron-molybdenum carbide eutectic catalytic system and the isotropic stress field. Near the particle surface, due to relatively low stress and easy catalyst accumulation, the degree of graphitization was high, and the crystals were fully formed. Inside the particles, due to the pinning effect of molybdenum carbide and the guidance of isotropic stress, graphite microcrystals intertwined and grew, forming an isotropic orientation similar to a "card layer" structure. After the holding period, the furnace was naturally cooled to room temperature to obtain graphitized bulk materials.

[0044] Step 5: Dissociation and Grading Processing The purpose of this step is to break down the bulk material into individual particles and obtain a final product that meets the particle size requirements of lithium-ion battery anode materials through crushing and grading.

[0045] First, the graphitized block obtained in step 4 is subjected to mechanical coarse crushing. Jaw crushers, hammer crushers, or other equipment can be used to crush the block into particles with a diameter of less than 5 mm, for example, all of them can be crushed to less than 3 mm.

[0046] The coarsely crushed particles undergo magnetic separation to remove iron impurities that may have been introduced from the equipment during the crushing process. The magnetic field strength for this process is between 8000 and 12000 Gauss. The strong magnetic field adsorbs and separates ferromagnetic impurities, ensuring product purity.

[0047] The coarsely crushed particles are then subjected to fine grinding and spheroidization using an air jet mill. The operating parameters of the air jet mill are set as follows: grinding pressure 0.6 MPa to 0.8 MPa, for example 0.7 MPa; classifying wheel speed 2500 rpm to 3500 rpm, for example 3000 rpm. Driven by the high-speed, high-pressure airflow, the particles undergo intense collisions and friction, thereby achieving dissociation and fine grinding. Simultaneously, under the centrifugal force field generated by the high-speed rotation of the classifying wheel, fine particles that meet the particle size requirements are separated in a timely manner, while coarse particles are returned to the grinding zone for further grinding. This process also simultaneously completes the spheroidization of the particles, making the particle edges more rounded, which is beneficial to improving the processing performance and electrochemical performance of the negative electrode material.

[0048] Finally, the powder collected after air-jet milling undergoes precise classification. The classification equipment can employ an ultrasonic vibrating screen, which precisely controls the particle size distribution of the product by combining screens with different aperture sizes. For example, a combination of an upper screen with an 18-micron aperture and a lower screen with a 10-micron aperture can be used. The ultrasonic generator and vibration motor are turned on, and a suitable amplitude (e.g., 2.0 mm) is set. Under the combined action of ultrasonic waves and mechanical vibration, particles larger than 18 microns are trapped by the upper screen, particles between 10 and 18 microns pass through the upper screen and are collected by the lower screen, while particles smaller than 10 microns pass through the lower screen as fine powder and are removed. The undersize material collected from the lower screen is the final graphite material for lithium-ion battery anodes.

[0049] Through the above steps, the present invention successfully prepared a graphite material for lithium-ion battery anodes that combines high capacity, high initial coulombic efficiency, excellent rate performance, and long cycle life.

[0050] This invention addresses the technical bottleneck of existing artificial graphite materials for lithium-ion battery anodes, which cannot simultaneously achieve high specific capacity and high rate performance. It provides a catalytically assisted graphitization method through iron-molybdenum bimetallic catalysis and stress field synergistic regulation. The core of this method lies in introducing an isotropic mechanical stress field during graphite crystallization growth using a specific process combination. By utilizing the pinning effect of molybdenum carbide, a unique microstructure is constructed—one with a highly graphitized surface and an isotropic interwoven interior—thereby achieving a synergistic improvement in the capacity and fast-charging performance of the lithium-ion battery anode material.

[0051] Example 1 This embodiment describes in detail the specific process of preparing graphite material for lithium battery anodes according to the technical solution of the present invention.

[0052] Step 1: Preparation and Pretreatment of Composite Catalyst The goal of this step is to uniformly load the iron-molybdenum bimetallic catalyst precursor in ionic form onto the surface and internal pores of spherical mesophase carbon microsphere powder, laying the foundation for subsequent high-efficiency catalysis.

[0053] First, 1000 grams of spherical mesophase carbon microsphere powder was weighed as a carbonaceous precursor. This spherical mesophase carbon microsphere powder has an isotropic structure with a D50 particle size of 3.2 micrometers and a particle size distribution ranging from 2 to 5 micrometers. This isotropic spherical structure is beneficial for the subsequent formation of a uniform stress field.

[0054] 1000g of spherical mesophase carbon microsphere powder was slowly added to a reactor containing 2300g of deionized water. The stirrer was turned on and set to 300 rpm, and stirring was continued for 15 minutes to form a uniform suspension. The solid content of the suspension at this point was calculated to be 1000g divided by (1000g + 2300g), resulting in approximately 30.3%, which meets the solid content requirement of 25% to 35%.

[0055] Two catalyst precursors were weighed separately. The first was ferric nitrate nonahydrate, with the chemical formula Fe(NO3)3·9H2O. According to the design requirements, the iron content should be 3% to 5% of the mass of the spherical mesophase carbon microsphere powder; in this embodiment, the midpoint of 4% was used. Therefore, the required iron content is 1000 grams multiplied by 4%, which is 40 grams. The mass fraction of iron in ferric nitrate nonahydrate is approximately 0.1386, calculated by dividing the iron atomic weight of 56 by the molecular weight of ferric nitrate nonahydrate (404). Therefore, the required mass of ferric nitrate nonahydrate is 40 grams divided by 0.1386, resulting in approximately 288.6 grams. 289 grams were actually weighed.

[0056] The second catalyst precursor is ammonium molybdate, with the chemical formula (NH4)6Mo7O. 24 • 4H₂O. According to the design requirements, the mass of molybdenum should account for 0.5% to 1.5% of the mass of the spherical mesophase carbon microsphere powder; in this embodiment, the midpoint of 1.0% is used. Therefore, the required mass of molybdenum is 1000 grams multiplied by 1.0%, which is 10 grams. The mass fraction of molybdenum in ammonium molybdate is approximately 0.543, calculated as molybdenum atomic weight 95.94 multiplied by 7 divided by the molecular weight of ammonium molybdate 1236. Therefore, the required mass of ammonium molybdate is 10 grams divided by 0.543, resulting in approximately 18.4 grams. 18.4 grams were actually weighed.

[0057] 289 g of ferric nitrate nonahydrate and 18.4 g of ammonium molybdate were weighed and added sequentially to the suspension in the above-mentioned reactor. The water bath temperature of the reactor was set to 70 degrees Celsius and maintained at this temperature for 5 hours with continuous stirring. The stirring speed was maintained at 300 rpm. During this process, ferric nitrate nonahydrate and ammonium molybdate completely dissolved, releasing iron ions and molybdate ions. Due to the abundant oxygen-containing functional groups and nanoscale pores on the surface of the mesophase carbon microspheres, iron ions and molybdate ions fully penetrated into the surface and internal pores of the spherical mesophase carbon microsphere powder through adsorption and diffusion, achieving uniform loading at the molecular level.

[0058] After adsorption, the mixture is pumped to a spray dryer via a peristaltic pump for spray drying and granulation. The inlet temperature of the spray dryer is set to 220 degrees Celsius, and the outlet temperature to 95 degrees Celsius. A centrifugal atomizing disc is used, with a rotation speed of 18,000 rpm. In the high-temperature airflow, the droplets are instantly dried, yielding composite microsphere powder loaded with an iron-molybdenum bimetallic catalyst precursor. This powder retains its original spherical morphology, and there is no surface enrichment of the catalyst precursor.

[0059] Step 2: Asphalt Fusion Coating and Block Forming The goal of this step is to construct a dense green block through asphalt coating and isostatic pressing, providing a structural basis for the establishment of the stress field during the subsequent carbonization process.

[0060] All the composite microsphere powder obtained in step 1 (approximately 1307 grams, including microspheres and catalyst) was added to a Z-type kneader. 200 grams of medium-temperature coal tar pitch was weighed as a coating agent. This medium-temperature coal tar pitch has a softening point of 85 degrees Celsius and a quinoline-insoluble content of 4.5%, meeting the requirements of a softening point of 80 to 90 degrees Celsius and a quinoline-insoluble content of less than 5%. The mass ratio of the composite microsphere powder to the medium-temperature coal tar pitch was 1307:200, which translates to approximately 100:15.3, satisfying the mass ratio requirement of 100:15 to 100:20.

[0061] The Z-type kneader was heated to 160 degrees Celsius, and stirring was started. The mixture was heated and mixed at 160 degrees Celsius for 45 minutes. As the temperature rose, the medium-temperature coal tar pitch gradually melted into a liquid phase with good fluidity. Under the strong shearing and mixing action of the kneader blades, the molten medium-temperature coal tar pitch was evenly spread and coated on the surface of each composite microsphere powder, forming a paste-like mixture with a certain fluidity.

[0062] The paste-like mixture is removed from the kneader and quickly transferred to a vacuum degassing tank for degassing. The degassing time is set to 15 minutes, and the degassing vacuum degree is maintained below 50 Pa. Degassing effectively removes air bubbles trapped during the mixing process, preventing defects from occurring during subsequent molding and carbonization.

[0063] After degassing, the paste-like mixture is filled into a pre-formed rubber mold. The inner cavity of the rubber mold is cylindrical, with a diameter of 100 mm. During filling, the mold is slightly vibrated to ensure dense material filling. After sealing the mold, it is placed in the working cylinder of a cold isostatic press. The isostatic press is started, a pressure of 220 MPa is applied, and this pressure is maintained for 12 minutes. Under the ultra-high hydrostatic pressure of 220 MPa, the composite microsphere powder particles coated with asphalt undergo rearrangement and plastic deformation, maximizing the elimination of interparticle gaps, ultimately yielding a highly dense, defect-free cylindrical composite green block.

[0064] Step 3: Gradient carbonization treatment The goal of this step is to induce carbonization of the asphalt through a precisely controlled heating process, and to generate isotropic mechanical stress within the block by utilizing its volume shrinkage.

[0065] The cylindrical composite green body obtained in step 2 is placed in the constant temperature zone of the atmosphere-protected carbonization furnace. The furnace door is closed, and the vacuum pump is started to perform a vacuuming-nitrogen purging operation on the furnace chamber, repeated three times to ensure that the oxygen volume concentration in the furnace is below 10 parts per million. Then, a nitrogen atmosphere is maintained, with the gas flow rate controlled at 10 liters / minute, and the furnace pressure maintained at a slightly positive pressure of about 200 Pa.

[0066] The heating program is initiated for gradient temperature carbonization. The first stage involves slowly heating from room temperature (25°C) to 380°C at a rate of 0.8°C / min. After reaching 380°C, the temperature is held for 150 minutes. This low-temperature, slow heating stage aims to allow the medium-temperature coal tar coating on the particle surface to undergo slow melting, cross-linking, and preliminary carbonization, forming a semi-coke-like outer shell with a certain strength. During the formation of this shell, the significant volume shrinkage associated with tar carbonization applies a uniform, isotropic compressive stress to the internal composite microsphere powder. The establishment of this stress field is crucial for the subsequent formation of the isotropic graphite structure.

[0067] The second stage: The temperature continues to rise from 380°C to 1050°C at a heating rate of 2.5°C / min. After reaching 1050°C, it is held for 210 minutes. During this stage, the composite microsphere powder itself and the semi-coke-like outer shell covering its surface undergo deep carbonization, releasing a large amount of small molecule gas. The carbon skeleton further condenses, ultimately forming a fully carbonized block with a certain mechanical strength. Simultaneously, the ferric nitrate nonahydrate and ammonium molybdate loaded in the microsphere pores decompose at high temperature, transforming into nano-sized iron oxide and molybdenum oxide particles, which are uniformly embedded in the carbon skeleton of the carbonized block. After the holding period, the furnace is allowed to cool naturally to room temperature, and the carbonized block is then removed.

[0068] Step 4: High-temperature catalytic graphitization treatment This step is the core of the invention, which utilizes the synergistic effect of catalyst and stress field at high temperature to achieve the control of microstructure.

[0069] The carbonized block obtained in step 3 is placed in the central area of ​​an Atchison-type graphitization furnace. The furnace is sealed, and the atmosphere inside the furnace is purged with argon gas three times. Afterward, the argon atmosphere is maintained, with the gas flow rate controlled at 8 liters / minute, and a slight positive pressure of approximately 150 Pa is maintained inside the furnace.

[0070] Turn on the heating power of the graphitization furnace and raise the furnace temperature from room temperature to 2700 degrees Celsius at a heating rate of 6 degrees Celsius per minute. After reaching 2700 degrees Celsius, hold at that temperature for 150 minutes.

[0071] During the heating process, when the temperature exceeds 1000 degrees Celsius, the nano-sized iron oxides and molybdenum oxides embedded in the carbonized mass begin to be reduced by carbon. The specific reaction is as follows: Iron oxides are reduced to elemental iron by carbon: Molybdenum oxide is reduced by carbon and further reacts with carbon to form molybdenum carbide: As the temperature continues to rise to approximately 1300 degrees Celsius or higher, the generated elemental iron and molybdenum carbide form an iron-molybdenum carbide eutectic catalytic system. This eutectic system is liquid and possesses extremely high catalytic activity, capable of dissolving surrounding carbon atoms and, driven by temperature or concentration gradients, causing carbon atoms to recrystallize in the form of graphite crystals.

[0072] In this process, two key factors work together to determine the final microstructure of graphite: First, the isotropic mechanical stress field formed during carbonization in step 3 still exists inside the bulk. This stress field provides energy guidance for the rearrangement of carbon atoms and the growth of graphite crystallites, causing the C-axis of the graphite crystallites to tend to be preferentially oriented along the stress direction. However, since the stress is isotropic, this preferential orientation exists in all directions.

[0073] Secondly, the in-situ generated molybdenum carbide particles possess extremely high melting points (approximately 2600 degrees Celsius) and chemical stability. In the liquid iron-molybdenum carbide eutectic system, they act as heterogeneous nucleation sites and pinning points. The molybdenum carbide particles pin to the grain boundaries of the growing graphite crystallites, effectively limiting excessive growth and unidirectional growth along a specific direction.

[0074] After being held at 2700 degrees Celsius for 150 minutes, a unique microstructure was formed through the long-term synergistic effect of the iron-molybdenum carbide eutectic catalytic system and the isotropic stress field. Near the particle surface, due to lower stress and easier catalyst accumulation, the degree of graphitization was high, and the crystals were fully formed. Inside the particles, due to the pinning effect of molybdenum carbide and the guidance of isotropic stress, graphite microcrystals intertwined and grew, forming an isotropic orientation similar to a "card layer" structure. After the holding period, the furnace was naturally cooled to room temperature to obtain graphitized bulk materials.

[0075] Step 5: Dissociation and Grading Processing The goal of this step is to dissociate the bulk material into individual particles and obtain a particle size distribution that meets the requirements of anode materials through grading.

[0076] The graphitized blocks obtained in step 4 are first coarsely crushed using a jaw crusher. The discharge gap of the jaw crusher is adjusted so that the particle size of all crushed particles is less than 3 mm, meeting the requirement of being less than 5 mm.

[0077] The coarsely crushed particles undergo magnetic separation for iron removal. The specific operation is as follows: A dry electromagnetic separator is used. The coarsely crushed particles are uniformly fed into the magnetic separation zone via a vibrating feeder at a feeding rate of 80 kg / h, with the magnetic field strength set to 10,000 Gauss. Under the influence of the strong magnetic field, ferromagnetic impurities (such as iron filings generated during equipment wear during crushing) are adsorbed onto the surface of the magnetic rollers, while non-magnetic graphite particles pass through freely. The particles passing through the magnetic separator are collected, completing the iron removal process.

[0078] The coarsely crushed particles are evenly fed into the main unit of the air jet mill via a vibrating feeder. The operating parameters of the air jet mill are set as follows: milling pressure of 0.7 MPa and classifying wheel speed of 3000 rpm. Driven by the high-speed, high-pressure airflow, the particles undergo intense collisions and friction, achieving dissociation and fine crushing. Simultaneously, under the centrifugal force field generated by the high-speed rotation of the classifying wheel, fine particles meeting the particle size requirements are separated, while coarse particles return to the crushing zone for further crushing. This process also completes the spheroidization of the particles, making their edges more rounded.

[0079] The powder exiting the air jet mill is collected. The powder is then precisely classified using an ultrasonic vibrating screen. The screen has two layers: an upper screen with an 18-micron aperture and a lower screen with a 10-micron aperture. The ultrasonic generator and vibration motor are turned on, and the amplitude is set to 2.0 mm. Under the combined action of ultrasonic waves and mechanical vibration, particles larger than 18 microns are retained by the upper screen, particles between 10 and 18 microns pass through the upper screen and are collected by the lower screen, while particles smaller than 10 microns pass through the lower screen and are removed as fine powder.

[0080] The material collected from the lower sieve is the final graphite material for lithium-ion battery anodes prepared in this embodiment. The D50 particle size of this material is approximately 14.5 micrometers, with a concentrated particle size distribution.

[0081] Comparative Example 1 This comparative example uses a conventional powder-catalyzed graphitization method to illustrate the necessity of asphalt coating, molding, and stress field construction in this invention.

[0082] Step 1: Weigh 1000 grams of spherical mesophase carbon microsphere powder (D50=3.2 micrometers) that is exactly the same as that in Example 1.

[0083] Step 2: Weigh 289 g of ferric nitrate nonahydrate and 18.4 g of ammonium molybdate, dissolve them in 1500 g of deionized water, and stir until homogeneous to obtain a mixed solution. Add 1000 g of spherical mesophase carbon microsphere powder to this mixed solution and stir for 4 hours to form a slurry. Then place the slurry in a forced-air drying oven and dry it at 120 degrees Celsius for 24 hours to obtain a dry powder loaded with the iron-molybdenum catalyst precursor. Spray drying was not performed in this step, resulting in slightly less uniform catalyst distribution.

[0084] Step 3: Place the dried powder obtained in Step 2 directly into a graphitization furnace and perform high-temperature graphitization treatment according to the same heating curve as Step 4 of Example 1: Under argon protection, heat to 2700 degrees Celsius at 6 degrees Celsius / minute and hold for 150 minutes.

[0085] Step 4: Take out the graphitized sintered block (loose), crush it to less than 3 mm with a jaw crusher, then crush it with an air jet mill under the same parameters (crushing pressure 0.7 MPa, classifying wheel speed 3000 rpm), and finally classify it with an ultrasonic vibrating screen to collect the 10 to 18 micrometer undersize material as the negative electrode material of Comparative Example 1.

[0086] Comparative Example 2 This comparative example uses a non-catalytic molding graphitization method to illustrate the necessity of the iron-molybdenum bimetallic catalyst system in this invention.

[0087] Step 1: Weigh 1000 grams of spherical mesophase carbon microsphere powder (D50=3.2 micrometers) that is exactly the same as in Example 1, without adding any catalyst.

[0088] Step 2: Mix the powder with 200g of the same medium-temperature coal tar pitch as in Example 1 in a Z-type kneader at 160 degrees Celsius for 45 minutes to obtain a paste-like mixture.

[0089] Step 3: After vacuum degassing the paste mixture (50 Pa, 15 minutes), fill it into a rubber mold and perform cold isostatic pressing at 220 MPa for 12 minutes to obtain a composite green block.

[0090] Step 4: Place the composite green block in a carbonization furnace and perform gradient carbonization treatment according to the same procedure as Step 3 of Example 1: raise the temperature to 380 degrees Celsius at 0.8 degrees Celsius / minute (hold for 150 minutes), and then raise the temperature to 1050 degrees Celsius at 2.5 degrees Celsius / minute (hold for 210 minutes) to obtain the carbonized block.

[0091] Step 5: Place the carbonized block in a graphitization furnace and perform high-temperature graphitization treatment according to the same procedure as Step 4 of Example 1: Under argon protection, raise the temperature to 2700 degrees Celsius at 6 degrees Celsius / minute and hold for 150 minutes to obtain the graphitized block.

[0092] Step 6: The graphitized bulk material is crushed, air-jet pulverized and classified in exactly the same manner as in Step 5 of Example 1, and the undersize material of 10 micrometers to 18 micrometers is collected as the negative electrode material of Comparative Example 2.

[0093] Performance testing and characterization The negative electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 were used as active materials to assemble CR2032 coin half-cells to evaluate their electrochemical performance. The specific steps are as follows: 96 grams of active material, 1 gram of conductive carbon black (Super P), 1.5 grams of styrene-butadiene rubber (SBR, an aqueous emulsion with a solid content of 50%, equivalent to 0.75 grams of dry rubber), and 1.5 grams of sodium carboxymethyl cellulose (CMC) were mixed. First, CMC was dissolved in deionized water to prepare a 1.5% (w / w) adhesive solution. Then, the active material and conductive carbon black were added, and the mixture was stirred evenly using a vacuum mixer. The SBR emulsion was then added, and stirring continued until a negative electrode slurry with a solid content of 48% was obtained. The slurry was uniformly coated onto a 10-micron thick copper foil and vacuum dried at 110 degrees Celsius for 12 hours. The dried electrode sheet was compacted using a roller press, with the compaction density controlled at 1.65 g / cm³, and then punched into circular negative electrode sheets with a diameter of 14 mm.

[0094] The battery was assembled in an argon-filled glove box. A lithium metal sheet was used as both the counter and reference electrodes. The separator was a Celgard 2400 polypropylene porous membrane. The electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent was a 1:1:1 volume ratio mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), with 2% vinylene carbonate (VC) added as a film-forming additive.

[0095] The assembled batteries underwent electrochemical testing at a constant temperature of 25 degrees Celsius. Charge-discharge tests were performed using the Blue Battery testing system. The voltage test range was 0.005 volts to 2.0 volts (relative to Li). + / Li). The degree of graphitization was measured by X-ray diffraction (XRD) and calculated according to the Mering-Maire formula: Where g represents the degree of graphitization. The interlayer spacing of the 002 crystal plane in the XRD pattern is the measured value in nanometers.

[0096] The test results are summarized in Table 1.

[0097] Table 1. Performance comparison data between the examples and comparative examples. Results analysis and discussion: First, Example 1 and Comparative Example 1 were compared. Comparative Example 1 used the same catalyst system and graphitization temperature as Example 1, but omitted the processes of pitch coating, isostatic pressing, and gradient carbonization to establish a stress field. The results showed that while the graphitization degree (91.5%) and capacity (352.3 mAh / g) of Comparative Example 1 were higher than the sample without a catalyst, they were still significantly lower than those of Example 1 (95.8%, 362.5 mAh / g). This indicates that the "micro-encapsulation" environment constructed by the molding process in this invention greatly suppresses catalyst escape at high temperatures, improves catalytic efficiency, and allows for more thorough graphitization. More importantly, the rate performance (5C / 0.1C capacity retention of 75.4%) and cycle stability (88.5%) of Comparative Example 1 were far inferior to those of Example 1 (92.1%, 96.2%). This suggests that without the guidance of a stress field and the pinning effect of molybdenum carbide, the graphite material obtained by simple catalysis has a single grain orientation, which is not conducive to rapid lithium-ion diffusion, and the structure is prone to collapse during cycling. This proves that the stress field construction process of "asphalt coating-isostatic pressing" is essential, and its combination with the catalytic system produces a significant synergistic effect.

[0098] Secondly, Comparative Example 1 and Comparative Example 2 were compared. Comparative Example 2 used the exact same molding and heat treatment process as Example 1, but without adding any catalyst. The results showed that Comparative Example 2 had the lowest degree of graphitization (89.8%) and capacity (345.6 mAh / g), failing to meet the requirements for high energy density. Although its rate performance (82.6%) and initial coulombic efficiency (93.8%) were better than Comparative Example 1, they were still significantly lower than Example 1. This indicates that without the efficient catalytic effect of the iron-molybdenum bimetallic catalyst, relying solely on stress field induction results in incomplete graphitization transformation and limited capacity improvement. This proves that the "iron-molybdenum bimetallic catalytic system" is key to achieving breakthroughs in high capacity.

[0099] In summary, Example 1 is not simply a combination of "catalysis" and "molding," but rather a sophisticated process design that enables the two to produce a strong synergistic effect in a unified system: the molding process provides a "micro-encapsulation" environment for the catalyst to function efficiently and introduces a stress field, while the catalytic system, under the stress field, not only increases the degree of graphitization, but also shapes a unique isotropic interwoven microstructure through the pinning effect with molybdenum carbide.

[0100] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A catalytic-assisted graphitization method of a graphite material for a lithium battery negative electrode, characterized by, Includes the following steps: Step 1: Spherical mesophase carbon microsphere powder is mixed with ferric nitrate nonahydrate and ammonium molybdate in the liquid phase and then spray-dried to obtain composite microsphere powder loaded with iron-molybdenum bimetallic catalyst precursor; The particle size range of the spherical mesophase carbon microsphere powder in step 1 is 2 micrometers to 5 micrometers; the amount of ferric nitrate nonahydrate added is calculated as 3% to 5% of the mass of iron element in the spherical mesophase carbon microsphere powder; the amount of ammonium molybdate added is calculated as 0.5% to 1.5% of the mass of molybdenum element in the spherical mesophase carbon microsphere powder. The spherical mesophase carbon microsphere powder mentioned in step 1 has an isotropic structure and a D50 particle size of 2.5 micrometers to 3.5 micrometers. Step 2: The composite microsphere powder is heated and mixed with medium-temperature coal tar pitch to coat the surface of the composite microsphere powder with the molten medium-temperature coal tar pitch to form a paste mixture. The paste mixture is then cold isostatically pressed to obtain a dense composite green block. The softening point of the medium-temperature coal tar pitch mentioned in step 2 is 80 to 90 degrees Celsius, and the quinoline insoluble content is less than 5%. In step 2, the mass ratio of the composite microsphere powder to the medium-temperature coal tar pitch is 100:15 to 100:

20. Step 3: The composite green block is subjected to gradient heating carbonization treatment under an inert atmosphere. The volume shrinkage during the medium-temperature coal tar pitch carbonization process is used to apply isotropic mechanical stress to the internal composite microsphere powder to obtain a carbonized block. Step 4: The carbonized block is subjected to high-temperature catalytic graphitization treatment under an argon atmosphere, so that the iron-molybdenum bimetallic catalyst precursor forms an iron-molybdenum carbide eutectic catalytic system that induces carbon atom rearrangement under the combined action of mechanical stress, forming a highly crystalline graphite structure with high surface graphitization and isotropic interwoven interior, thus obtaining a graphitized block. The molybdenum carbide acts as a pinning agent within the carbonized bulk, limiting the excessive growth and single orientation of graphite crystallites. During the high-temperature catalytic graphitization process, the ferric nitrate nonahydrate and ammonium molybdate introduced in step 1 are first reduced by carbon to elemental iron and molybdenum carbide in the carbonized block, thereby forming the iron-molybdenum carbide eutectic catalytic system. Step 5: The graphitized bulk material is mechanically crushed, air-jet pulverized and graded to collect powder within the target particle size range, which is the final graphite material for lithium battery anodes.

2. The method according to claim 1, wherein the method is characterized by: The liquid-phase mixing process is as follows: First, the spherical mesophase carbon microsphere powder is dispersed in deionized water to form a suspension with a solid content of 25% to 35%. Then, the ferric nitrate nonahydrate and the ammonium molybdate are dissolved in the suspension. The mixture is stirred continuously for 4 to 6 hours at a water bath temperature of 60 to 80 degrees Celsius to allow iron ions and molybdate ions to be fully adsorbed and penetrated into the surface and internal pores of the spherical mesophase carbon microsphere powder. The inlet temperature of the spray dryer is 210 to 230 degrees Celsius, and the outlet temperature is 90 to 100 degrees Celsius.

3. The method according to claim 1, wherein the method is characterized by: The heating and mixing temperature is 150°C to 180°C, and the mixing time is 30 minutes to 60 minutes; the cold isostatic pressing pressure is 200 MPa to 250 MPa, and the holding time is 10 minutes to 15 minutes.

4. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, The gradient heating carbonization process described in step 3 specifically includes: first, heating from room temperature to 350 to 400 degrees Celsius at a heating rate of 0.5 to 1 degree Celsius per minute, and holding at that temperature for 120 to 180 minutes, so that the coated medium-temperature coal tar pitch undergoes slow melting, cross-linking, and preliminary carbonization to form a semi-coke-like outer shell; then, heating at a heating rate of 2 to 3 degrees Celsius per minute to 1000 to 1100 degrees Celsius, and holding at that temperature for 180 to 240 minutes, so that the composite microsphere powder and the semi-coke-like outer shell are completely carbonized.

5. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, The heating rate of the high-temperature catalytic graphitization treatment in step 4 is 5°C / min to 8°C / min, the maximum temperature is 2600°C to 2800°C, and the holding time is 120 minutes to 180 minutes.

6. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, The mechanical crushing in step 5 involves crushing the graphitized block into particles with a diameter of less than 5 mm; the air jet milling is carried out under the conditions of a crushing pressure of 0.6 MPa to 0.8 MPa and a classifying wheel speed of 2500 rpm to 3500 rpm for fine crushing and spheroidization; the classification process is carried out by precise classification through an ultrasonic vibrating screen, and the collected target particle size range is 10 micrometers to 18 micrometers.

7. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, The cold isostatic pressing molding in step 2 uses a rubber mold. The paste mixture is first degassed under vacuum before being filled into the rubber mold. The degassed time is 10 to 20 minutes and the degassed vacuum degree is less than 50 Pa.

8. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, In steps 3 and 4, the gas flow rates of the inert atmosphere and the argon atmosphere are independently controlled between 5 liters / minute and 15 liters / minute to ensure that the pressure inside the furnace is in a slightly positive pressure state, with a pressure range of 100 Pa to 300 Pa.

9. The catalytic-assisted graphitization method for graphite materials used in lithium battery anodes according to claim 1, characterized in that, In step 5, the particles after mechanical crushing are subjected to magnetic separation to remove iron impurities introduced during the crushing process before airflow pulverization; the magnetic field strength of the magnetic separation is 8000 Gauss to 12000 Gauss.

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