A method for preparing a spherical graphite composite material for an LFP battery

Abstract

The application discloses a kind of spherical graphite composite material preparation methods for LFP battery, belong to lithium iron phosphate battery negative material preparation technical field.Method includes: S1 raw material pretreatment and pre-spheroidization;S2 fine shaping, in turn, ultra-high-speed airflow crushing shaping, series airflow classification mill shaping and ultrasonic shaping;S3 depth purification, before pickling, remove magnetism, multi-stage pickling, drying, low-frequency resonance mixing and pickling, remove magnetism after S4 particle size screening;S5 fluidized field reconstruction coating, using high soft point petroleum-based pitch, by constructing temperature-airflow field coating and ladder carbonization;S6 finished product integration and refining.The prepared spherical graphite composite material is not the extreme of single index pursuit, but realizes good balance and synergy between multiple key performances, provides comprehensive, reliable and practical application value negative electrode solution for LFP battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate battery anode material preparation technology, and relates to a method for preparing spherical graphite composite materials for LFP batteries. Background Technology

[0002] Spherical graphite anode materials are the preferred choice for LFP battery anode materials due to their high tap density, good isotropy, and stable electrochemical performance. However, in practical applications of high-performance LFP batteries, existing spherical graphite exhibits performance shortcomings: specific capacity and initial efficiency are difficult to achieve simultaneously at ideal levels. The specific capacity of conventional spherical graphite is typically 350-360 mAh / g, and the initial coulombic efficiency is approximately 90%-92%, still falling short of the theoretical capacity of graphite (372 mAh / g). These insufficient capacity and initial efficiency directly limit the potential for increasing the energy density of LFP batteries. There is a contradiction between high-rate charge / discharge performance and cycle life: LFP batteries are often designed to support fast charging due to their excellent safety characteristics. However, traditional spherical graphite often experiences accelerated capacity decay and even lithium plating when subjected to high-rate charge / discharge (e.g., above 2C) due to insufficient interfacial kinetics. Insufficient cycle stability makes it difficult to match the long lifespan advantage of LFP cathodes: While LFP cathodes have a long cycle life, conventional spherical graphite anodes experience a significant drop in capacity retention after 2000 cycles, becoming a bottleneck in overall battery life. The main reason is uneven or poorly compact coating layers, leading to continuous electrolyte penetration during cycling, causing the SEI film to thicken and irreversibly deplete active lithium. High impurity content affects battery safety and self-discharge performance: Traditional purification processes struggle to reduce magnetic impurities (Fe, Co, Ni, Cr, Zn, etc.) to extremely low levels. Residual trace metal impurities may trigger micro-short circuits or catalytic side reactions during charge and discharge, posing a potential threat to the high safety and low self-discharge rate that LFP batteries should possess.

[0003] With the rapid expansion of the market and increasingly fierce competition, battery manufacturers have put forward requirements for spherical graphite for negative electrodes that far exceed the conventional solid content indicators. They are now pursuing deeper and more refined performance parameters, and the requirements for the overall cost, batch consistency and electrochemical durability of materials are becoming increasingly stringent. However, the existing industrial preparation process of spherical graphite—which covers key processes such as raw material crushing, spheroidization and shaping, purification and surface coating—has exposed the following technical defects when meeting the above-mentioned stringent requirements: Crushing and spheroidization and shaping: In order to meet customers' requirements for high sphericity and narrow particle size distribution, high-impact and high-shear equipment is often used. Although spherical particles can be obtained quickly, over-crushing and over-spheroidization are very likely to occur during the production process. This results in a large amount of graphite raw material being over-ground into fine tailings, causing a waste of valuable graphite resources and significantly increasing the material and processing costs of large-scale production. At the same time, the strong mechanical impact induces a large number of microcracks, lattice distortion and other subsurface damage inside the graphite particles, which become hidden dangers for uneven electrolyte wetting and cycle failure. Furthermore, conventional series airflow classifier milling and shaping routes reveal fundamental limitations when scaled up: as throughput increases, the fluctuation range of product particle size D50 widens, batch-to-batch stability becomes difficult to control, and shaping efficiency cannot meet the requirements of large-scale continuous production.

[0004] Purification process: Existing purification technologies separate chemical purification and physical demagnetization into isolated operations. This fails to achieve a refined and coupled acid washing process, nor does it establish a multi-node demagnetization defense line throughout the entire process. It also fails to achieve synergy with upstream and downstream processes. Currently, traditional single-acid immersion or simple stirring and mixing methods are mostly used. There is a lack of refined design of the acid addition sequence, concentration gradient and reaction kinetic conditions. The problem of excessive acid use is common, resulting in low acid utilization efficiency. The current practice of only performing demagnetization in the last step cannot effectively deal with the risk of magnetic foreign matter introduction throughout the entire process. Magnetic particles may be encapsulated inside the carbon layer, forming embedded impurities that are difficult to eliminate, making it difficult to ensure the high purity and high consistency of spherical graphite composite materials.

[0005] Surface Coating and Carbonization: For the surface modification of spherical graphite, existing asphalt coating technologies generally suffer from poor coating thickness uniformity and unsatisfactory carbonization effects. In traditional processes, conventional coating often employs mechanical mixing or simple heat treatment, failing to differentiate the design based on the varying physicochemical evolution characteristics of asphalt at different temperature ranges. Viewing the coating and carbonization processes in isolation directly results in uneven spreading of the asphalt-based coating agent on the graphite surface, easily leading to localized accumulation or exposed areas. This uneven coating layer leads to poor interfacial stability, making it difficult to effectively suppress side reactions during cycling. In subsequent carbonization, numerous penetrating pores easily appear in the carbon layer, preventing the formation of a dense, continuous, and firmly adhered protective layer, resulting in performance fluctuations in the composite material between different batches.

[0006] In summary, existing spherical graphite preparation processes face core technological bottlenecks that restrict product consistency, electrochemical performance, and production costs across key stages, including crushing and shaping, purification, and surface coating carbonization. Therefore, there is an urgent need to develop a synergistic optimization method for the entire process, from raw material crushing to finished product refining, to systematically address the comprehensive challenges of spherical graphite in terms of sphericity, purity, coating uniformity, and batch stability, in order to meet the requirements of LFP batteries for low-defect, long-life, high-purity, and interfacially stable spherical graphite composite materials. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a method for preparing spherical graphite composite materials for LFP batteries.

[0008] The present invention provides a method for preparing spherical graphite composite materials for LFP batteries, specifically including the following steps:

[0009] S1. Raw Material Pretreatment and Pre-spheroidization: High-carbon flake graphite raw materials are subjected to impurity removal, dispersion, crushing, and pre-spheroidization flexible shaping treatment to obtain pre-spheroidized graphite. The requirements for high-carbon flake graphite raw materials are: particle size no greater than 100 mesh, and carbon content of 95-96%. From a cost and process perspective, graphite raw materials with a carbon content of 95-96% and a particle size no greater than 100 mesh are selected, mainly based on the following two points: Cost perspective: 95-96% carbon content is ordinary industrial-grade flake graphite, and the procurement cost is much lower than that of high-purity graphite. A particle size no greater than 100 mesh is a medium to fine specification, which avoids the high cost of purchasing ultrafine powders and provides a suitable starting particle size for subsequent crushing and shaping processes, making the overall raw material cost controllable. Process perspective: In actual production, the finer the better, as it saves time. However, in actual production, 80-100 mesh high-carbon flake graphite raw materials are mainly selected, which is conducive to achieving closed-loop linkage control in crushing and pre-spheroidization treatment and reducing the over-crushing rate. If the raw material is too coarse (e.g., greater than 100 mesh), a longer grinding time is required, which can easily cause lattice damage; if it is too fine, it can easily be over-grinded. This particle size range balances shaping efficiency and structural integrity, facilitating subsequent flexible shaping and purification.

[0010] In the impurity removal and dispersion stage, a combined process of screening and negative pressure air separation is employed. The screening stage uses a screen with an integrated high-frequency micro-vibrator at the bottom to remove excessively coarse, uncrushed particles or agglomerates, as well as some excessively fine dust, controlling particle size distribution. The negative pressure air separation stage uses a negative pressure air separator equipped with a dispersing device at the feed inlet. Negative pressure air separation effectively removes lower-density, lighter impurities (such as some mineral fragments and dust) by controlling airflow. It also effectively disperses the raw materials, laying a foundation for the next stage of crushing.

[0011] Crushing Process: Design Reasons + Problem Solving: Implementing the principle of more crushing and less grinding to solve the problems of asynchronous crushing and grading, over-crushing, and missed selection of coarse particles; ensuring timely separation of qualified fine powder and immediate re-crushing of coarse particles, guaranteeing a concentrated particle size range from the source. In the crushing process, a horizontal ultrafine pulverizer and online grading linkage control system is adopted to achieve closed-loop linkage control of crushing and grading, reducing over-crushing rate while controlling particle size; the horizontal ultrafine pulverizer and online grading linkage control system includes a crushing device, the inlet of which is connected to a vibrating frequency conversion feeding device with a buffer bin; the outlet of the crushing device is connected to the inlet of the grading device, and a dispersing device is installed between the outlet of the crushing device and the inlet of the grading device; an anti-static device is installed at the inlet of the grading device (solving the problem: real-time breaking of static electricity in graphite micropowder). Electroagglomeration eliminates false coarse particles; material dispersion is more uniform, crushing efficiency is improved, and particle size consistency is significantly enhanced. The grading device is equipped with a particle size analyzer; the fine powder outlet of the grading device is connected to a cyclone collector, and the coarse powder outlet of the grading device is connected to the return port of the crushing device through a sealed return pipe. The crushing device, grading device, and vibrating frequency conversion feeding device are all electrically connected to the control device. The control device receives the particle size signal from the particle size analyzer in real time and adjusts the grading speed parameters of the grading device, the crushing parameters of the crushing device, and / or the feeding parameters of the frequency conversion feeding device according to the preset particle size range. The crushing device has a water-cooled jacket on its exterior; low-temperature fresh air is used for air intake; this avoids high-temperature oxidation of graphite, increased surface oxygen functional groups, and lattice damage; it is beneficial for subsequent spheroidization and shaping, and improves tap density; it adopts negative pressure closed-loop operation, and unqualified coarse particles from grading are returned to the crusher inlet through a sealed return pipe; the results are: no dust leakage, no secondary pollution; coarse particles do not fall to the ground, do not agglomerate, and do not cause pollution, improving finished product yield and product consistency.

[0012] Flexible shaping: Through structurally improved flexible crushing and shaping, the graphite particles undergo surface blunting and contour spheroidization, avoiding excessive crushing and lattice damage. Simultaneously, it efficiently removes surface impurities, laying a stable foundation for subsequent spheroidization and shaping. This addresses problems inherent in existing stirred mills, including uneven stress within the grinding chamber, material deviation and stratification, localized strong impacts leading to graphite sheet fracture and lattice damage, inconsistent blunting of edges and corners, turbulent media movement, uncontrollable grinding media trajectory, excessive impact, and insufficient shear friction. In the pre-spheroidization flexible shaping process, a vertical stirred mill and an online classification and linkage control grinding system are used to achieve integrated grinding, classification, and discharge operations. The online classification and linkage control principle is similar to the crushing and classification principle described earlier and will not be elaborated upon here. In vertical stirred mills, segmented stirring rotors and helical curved stirring arms are used to avoid increased graphite fracture rates caused by single strong impacts. The segmented stirring rotor is divided into dispersion, shearing, and fine grinding sections from top to bottom, with the diameter increasing progressively in each section. The inner wall of the grinding chamber is fitted with gradient guide bushings that match the segmented stirring rotors to reduce material deposition in corners and segregation due to particle size differences. The gradient guide bushings are configured as follows: Upper dispersion section: Shallow helical guide grooves are formed on the inner wall, with a helix angle of 15-20° and a circular arc groove shape; Function: Weaken impact, enhance dispersion, guide material to rise slowly and distribute evenly, avoid local aggregation, and protect graphite scales. The material is not broken; the medium gradient shear section has bidirectional intersecting spiral grooves on the inner wall with a spiral angle of 25°-30°; the forward and reverse spiral grooves are distributed alternately to form an intersecting turbulent flow trajectory, which forces the material to repeatedly shear and rub against the medium, efficiently stripping gangue minerals from the graphite surface without damaging the graphite matrix structure; the lower strong grinding and stabilizing section has densely toothed axial stabilizing grooves on the inner wall, with the groove shape being an axial straight groove with a rounded bottom transition, forming a step difference between the groove bottom and the groove surface, enhancing the rolling and friction effects of the medium; this improves the local grinding intensity, achieving edge blunting and pre-spherical contour shaping; at the same time, it stabilizes the medium flow state, prevents eddies and segregation, and ensures grinding uniformity.

[0013] S2. Fine shaping: The pre-spheroidized graphite is subjected to ultra-high speed airflow pulverization shaping, series airflow staged milling shaping and ultrasonic shaping in sequence to obtain shaped spheroidized graphite;

[0014] Currently, the most widely used process for graphite spheroidization is the series airflow classifier mill. However, this process often requires a longer processing time to achieve the target particle size and morphology. A solution is to improve the traditional production line by introducing a high-speed airflow pulverizer to replace most of the series airflow classifier mill, retaining only a portion at the rear for fine finishing. This improves efficiency while ensuring quality. The core of the high-speed airflow pulverizer technology lies in utilizing the enormous kinetic energy generated by supersonic airflow, causing graphite particles to collide and rub against each other during high-speed motion, thus achieving precise shaping and pulverization. It mainly consists of a compressed gas supply unit, a supersonic nozzle, a pulverizing chamber, a classifier, and a collection device. Its workflow is as follows: 1. Graphite material is uniformly fed into the pulverizing chamber through a precision feeding device; 2. The high-pressure gas is accelerated to supersonic speed (Mach 2-3) through a specially designed Laval nozzle; Supersonic nozzle optimization design: Computational fluid dynamics (CFD) simulation is used to optimize the nozzle structure, ensuring that the airflow velocity remains stable in the supersonic region, providing continuous and stable kinetic energy to the particles. 3. Graphite particles gain extremely high kinetic energy under the influence of supersonic airflow, resulting in violent collisions and friction within the grinding chamber; 4. Intelligent classification: A high-precision turbine classifier with frequency conversion control can adjust the classification accuracy in real time to ensure a concentrated particle size distribution in the product; particles that have met the requirements are separated in real time, with coarse particles returned for further processing; qualified products are discharged through a collection system for subsequent processing. The ultra-high-speed airflow pulverization system has high requirements for the particle size distribution and moisture content of the raw materials; through the pre-spheroidizing flexible shaping process in step S1 and the configuration of drying equipment at the front end, the drawbacks of over-spheroidization that can easily occur in the ultra-high-speed airflow pulverization shaping system are reduced, and the requirement of a moisture content of less than 0.5% is met.In the ultra-high-speed airflow pulverization and shaping process, while the use of an ultra-high-speed airflow pulverizer and shaper can improve work efficiency, its core shortcomings lie in the tendency for over-pulverization, resulting in excessive fine powder that affects profitability. Furthermore, the classification accuracy is limited: although a high-precision turbine classifier with frequency conversion control can achieve the desired particle size distribution, in high-capacity continuous operation scenarios, fluctuations in feed and changes in airflow pressure can still cause drift in classification accuracy, leading to fine powder mixing into the finished product and premature discharge of coarse powder, affecting product particle size consistency. Frequent manual parameter adjustments are required, increasing operational complexity. Therefore, the following improvements are made: establishing a multi-field coupled collaborative control system that links the airflow field, temperature field, particle field, and PLC control system. A model is constructed to achieve effective collisions between graphite particles and between particles and the wall surface through the coordinated control of the airflow field, temperature field, and particle field, avoiding over-shaping. A variable frequency buffer feeding device is adopted, which includes a buffer hopper with buffering and homogenization functions and a variable frequency feeder. A spiral variable frequency feeder is used, and the feeding speed can be adjusted in real time according to the pressure of the crushing chamber and the classification accuracy, ensuring that the feed rate matches the crushing efficiency and the sorting efficiency, and avoiding material accumulation. A negative pressure extraction system is installed at the connection between the classifier and the crushing chamber. The particles after collision are quickly extracted from the crushing chamber under negative pressure and enter the classifier for sorting, with no retention throughout the process. A closed loop of collision → rapid extraction → precise sorting → coarse powder return is achieved. By establishing a multi-field coupled collaborative control model of the airflow field, temperature field, and particle field for coordinated control, the crystal structure damage or over-refinement rate caused by excessive collision is reduced while completing rapid preliminary spheroidization shaping.

[0015] The process of establishing a multi-field coupled collaborative control model is as follows: By defining the devices associated with each field, collecting characteristic parameters of each field under multiple operating conditions, establishing a global database, constructing collaborative control logic between parameters of each field, embedding a PLC control device, and verifying and optimizing it through trial operation, the model achieves linkage control of the airflow field, temperature field, and particle field. The parameters involved in the establishment process include: airflow field parameters, temperature field parameters, and particle field parameters; among which, airflow field parameters include airflow velocity, inlet pressure, and airflow rate; temperature field parameters include the working temperature of the processing chamber and temperature regulation accuracy; and particle field parameters include feed parameters, particle concentration, particle residence time, and particle size detection parameters.

[0016] In the series airflow classifying mill shaping process, a Sync real-time particle size monitoring device, which combines laser diffraction with AI algorithms, is configured to provide timely feedback and adjust the classification parameters to control batch differences. A Venturi feeder is used. The Venturi feeder is designed with the following features for the Venturi tube structure: the contraction angle is designed to be 15-20° to ensure smooth airflow acceleration and avoid airflow distortion; an inclined feeding structure is adopted with an angle of 30-45° with the flow channel axis; and several evenly distributed auxiliary jet holes are set in the expansion section.

[0017] In the series airflow classifier mill shaping process, the following problems are prone to occur: distortion of the airflow pulverization energy field: when processing large batches of materials, the turbulence effect leads to an imbalance in the particle collision probability distribution. Boundary layer trap of the classifier: in large-scale production, the flow velocity at the edge of the classifier wheel decreases by 15-20%, and the escape rate of coarse particles increases sharply. Difference in raw material crystallization orientation: the sphericity deviation of flake graphite from different mineral sources can reach more than 5% under the same pulverization parameters. Therefore, an ultrasonic shaping section is added after the traditional airflow mill, and the air pressure gradient is adjusted through real-time particle size feedback (control accuracy ±0.03-0.05MPa) to ensure batch stability.

[0018] S3. Deep purification: The shaped spherical graphite is subjected to demagnetization before acid washing, multi-stage acid washing, drying, low-frequency resonance mixing of graphite, and demagnetization after acid washing in sequence to obtain purified spherical graphite.

[0019] Multi-stage pickling includes stepwise acid addition mixed acid pickling, pressure filtration and intermediate washing, and aqua regia pickling. The specific process of multi-stage pickling is as follows: Stepwise acid addition mixed acid pickling: Water and shaped spheroidized graphite are added to the first-stage pickling container in sequence, and acid solutions are added in the following order: First, hydrofluoric acid solution is added and reacted at 60±2℃ for a certain period of time. Then, concentrated hydrochloric acid is added and reacted in an acidic environment where hydrofluoric acid and hydrochloric acid coexist for a certain period of time at a reaction temperature of 65±2℃. Finally, concentrated nitric acid is added and reacted in an acidic environment where hydrofluoric acid, hydrochloric acid, and nitric acid coexist for a certain period of time at a reaction temperature of 70-75℃. The first-stage pickled material is obtained. Unlike the traditional method of simply mixing and "using one pot" as a whole, this method relies on a deep understanding of the impurity components and precise control of the chemical reaction process: First step: Hydrofluoric acid is added first to target siliceous impurities. Silicate impurities (such as quartz and mica) have stable structures and are difficult to dissolve in conventional inorganic acids. Therefore, hydrofluoric acid (HF) is preferentially added in the initial stage of the reaction. Its ability to react with silicon to form soluble fluorides (such as fluorosilicic acid) removes these impurities, opening pathways for the subsequent dissolution of metal impurities. The second step is hydrochloric acid. After hydrofluoric acid opens the structural pathways, concentrated hydrochloric acid is added. Hydrochloric acid is a cost-effective metal solvent, efficiently dissolving most metal oxides and exhibiting a synergistic effect with subsequent nitric acid. Its addition at this stage readily dissolves the metal impurities exposed during the HF treatment. The third step is nitric acid, which serves a dual purpose: strong oxidizing properties allow it to oxidize elemental metals and low-valence compounds on the graphite surface, converting them into high-valence soluble substances. Combined with the existing hydrochloric acid, it forms highly oxidizing aqua regia, further removing impurities. In this way, the concentration gradient and reaction kinetic conditions can be precisely designed, reducing the amount of acid used, especially hydrofluoric acid. In the final mixed acid, 5-6% hydrofluoric acid, concentrated hydrochloric acid and concentrated nitric acid forming 30%-35% aqua regia can achieve good pickling results.

[0020] Filtration and intermediate washing: After the first-stage acid washing material is pressure filtered, it is washed sequentially with dilute hydrochloric acid solution and water to obtain intermediate purified material. The purpose of using dilute hydrochloric acid is that hydrochloric acid is inexpensive. During the washing process, a low pH environment is maintained to inhibit the hydrolysis and precipitation of metal ions. At the same time, the desorption of impurities is enhanced through ion exchange and protonation, providing a clean graphite surface for subsequent aqua regia acid washing and reducing the amount of aqua regia used.

[0021] Aqua regia pickling: Water and intermediate purified material are added sequentially to the second-stage pickling container, followed by the addition of aqua regia solution for pickling at a temperature of 70-80℃. After pickling, ultrasonic-assisted washing with pure water is performed. The second-stage aqua regia pickling utilizes its strong oxidation and complexing capabilities to remove stubborn metallic impurities remaining from the previous step, providing double protection.

[0022] Pre-demagnetization effectively removes fine magnetic particles mixed in shaped spheroidized graphite, preventing these impurities from entering the subsequent multi-stage acid washing system. These impurities not only inefficiently consume hydrofluoric acid, hydrochloric acid, nitric acid, and other acids, reducing acid utilization efficiency, but also undergo secondary deposition or embed themselves in the micropores of the graphite surface after dissolving in an acidic environment, forming complex contaminants that are difficult to remove. Pre-demagnetization and post-demagnetization form a synergistic two-way protection: pre-demagnetization reduces the impurity load of the acid washing process, while post-demagnetization acts as a gatekeeper. The combination of the two ensures the ultra-high purity of the purified spheroidized graphite and provides a clean substrate surface for the subsequent coating process, preventing magnetic particles from being encapsulated by the coating layer and becoming a source of catalytic failure in long-term cycles.

[0023] Low-frequency resonant mixing: Through mechanical vibration at a specific frequency, the agglomerates are naturally loosened under the resonance effect, avoiding secondary breakage or surface scratches caused by high-energy stirring or high-speed mixing to spherical graphite, thus maintaining sphericity and crystal integrity. Promoting impurity exposure: Resonant mixing causes micron-level relative displacement between particles, re-exposing the particle surfaces encased within the agglomerates. This facilitates the capture of trace magnetic impurities in the subsequent demagnetization process after acid washing, improving demagnetization efficiency. This step achieves powder homogenization in a gentle, uniform, and clean manner, laying a high-quality material foundation for final demagnetization. The specific process is as follows: The material is conveyed to a mixing silo equipped with a low-frequency mechanical resonance device. The resonant vibrator at the bottom of the silo is turned on, setting the vibration frequency to 15Hz to 25Hz and the amplitude to 3mm to 6mm. While avoiding damage to the spherical morphology of the graphite, the particles generate macroscopic convection circulation and microscopic vibration homogenization within the silo, resulting in homogenized graphite.

[0024] S4. Particle size sieving: The purified graphite is subjected to particle size sieving to obtain spherical graphite to be coated that meets the requirements; the sphericity of the graphite to be coated is required to be ≥0.94.

[0025] S5. Fluidized Field Reconstruction Coating: Traditional methods for coating graphite with asphalt typically involve simply mixing asphalt and graphite in a mechanical mixer or kneading device at a certain ratio, followed by direct one-step heat treatment in a high-temperature furnace. During this process, the asphalt softens and melts as the temperature rises, spontaneously spreading onto the graphite surface due to surface tension, ultimately forming an amorphous carbon coating layer through high-temperature carbonization. This method has a short operation process and relatively simple equipment investment, but it lacks staged and precise control over the temperature field and reaction kinetics. This leads to localized agglomeration or flow of the melted asphalt, poor uniformity of the coating layer thickness, and concentrated escape of light components during carbonization, which can easily form penetrating pores, ultimately affecting the cycle stability and rate performance of the negative electrode material.

[0026] To overcome the above problems, the following solution is proposed: using high-soft-point petroleum-based asphalt as raw material, and employing fluidized field reconstruction technology, a multi-segment temperature-gas flow field is constructed and the heating rate, temperature nodes, and fluidized gas velocity at each stage are controlled to coat the spherical graphite to be coated. After the coating is completed, a stepped heating method is used for carbonization treatment to obtain surface-modified spherical graphite. The coating treatment includes four stages: a rapid pre-spreading stage, a slow melting and leveling stage, an extremely slow shaping and curing stage, and a stepped heating carbonization transition stage.

[0027] Parameters of high-soft-point petroleum-based asphalt: Soft point 255-260℃, ash content <0.1%; coking value 60-65%; quinoline insolubles 0.9-1%. The reasons for material selection are as follows: Formation of a dense carbon layer, reducing side reactions: A high softening point means a low content of light components in the asphalt, resulting in less gas escape during carbonization and the formation of a denser, less porous coating layer. This effectively blocks the electrolyte, preventing solvent co-intercalation and graphite layer peeling, while repairing cracks and defects on the graphite surface. A coking value of 60-65% helps form a complete coating layer, providing a stronger physical barrier for the graphite. Smoother carbonization process, fewer defects: The macromolecules of high-soft-point asphalt undergo a more gradual decomposition and polymerization reaction during carbonization, reducing the likelihood of violent deformation or gas impact, thus decreasing the possibility of coating layer cracking or defect formation. Reasons for petroleum-based: Extremely low ash content, improving purity: The ash content of petroleum-based asphalt can be controlled below 0.1%, far lower than some coal-based asphalt. Low ash content avoids the introduction of impurities and prevents them from becoming active sites for side reactions, which is crucial for improving material purity. The quinoline insoluble content is 0.9-1%. A low quinoline insoluble content means that the asphalt has better fluidity in the molten state, making it easier to spread on the graphite surface and achieve uniform coating. In contrast, coal tar pitch often contains more native quinoline insolubles, affecting the wetting effect. A more regular molecular structure is beneficial to performance: Petroleum-based asphalt generally has a more regular molecular structure and fewer impurity elements than coal-based asphalt, which is beneficial for optimizing the performance of the final carbonized layer. The median particle size D50 of the asphalt raw material after pulverization is controlled within the range of 1μm to 8μm; the preferred asphalt powder has a median particle size D50 of 2μm to 6μm, and its particle size distribution width satisfies the SPAN value ((D90-D10) / D50) being between 1.5 and 2.5 to ensure the consistency of the coating layer thickness. Meanwhile, to prevent coating defects caused by excessively large particles, the D90 particle size of the asphalt powder should not exceed 18 μm, and the D99 particle size should not exceed 24 μm. By pulverizing the asphalt to the above particle size range, sufficient contact, uniform softening, and leveling of the asphalt on the spherical graphite surface can be achieved in the subsequent rapid pre-spreading and slow melt-leveling sections, thereby forming a dense and complete coating layer, effectively improving the cycle stability and rate performance of the final composite material.

[0028] Multi-segment temperature-airflow field: First, the rapid pre-spreading section begins: room temperature → T1, with a heating rate of 6-8℃ / min, T1 being 300±5℃, and an operating gas velocity of 1.1-1.3 times Umf. The rationale for these parameters is: rapid heating: the asphalt softening point is 255-260℃, quickly passing through the temperature range below the softening point prevents asphalt powder from lingering at low temperatures for extended periods, thus avoiding localized agglomeration or adhesion to the walls, and shortening the process cycle. The final temperature of 300±5℃: slightly higher than the upper limit of the asphalt softening point, ensures the asphalt is fully softened but has not yet entered the zone of severe pyrolysis, providing a suitable viscosity for subsequent spreading. The gas velocity of 1.1-1.3 Umf: slightly higher than the minimum fluidization velocity, ensuring thorough mixing of graphite particles and asphalt powder to form a core-shell pre-coating structure, while preventing excessively high gas velocities from causing the asphalt powder to be prematurely blown out of the reactor.

[0029] After the heat preservation period, the process enters the slow melting and leveling section: T1→T2, with a heating rate of 1.5-2℃ / min, and a T2 temperature of 385±5℃. Operating gas velocity: 1.5-2.0 times Umf; Rationale for this parameter: Slow heating (1.5-2℃ / min): Within the critical viscosity window for asphalt melting and spreading, controlling the heating rate prolongs the residence time of the molten asphalt in the suitable viscosity range, allowing it to fully spread into a uniform liquid film under the shear force of the airflow, rather than flowing and agglomerating due to a sudden drop in viscosity caused by excessively rapid heating. Final temperature 385±5℃: This temperature is lower than the significant pyrolysis initiation temperature of asphalt, ensuring that the spreading process is completed without pyrolysis interference; simultaneously, at 385℃, the asphalt viscosity has dropped to a low level suitable for leveling, achieving a synergistic leveling effect of "slow heating + strong shear" in conjunction with the high gas velocity. High gas velocity (1.5-2.0 Umf): High gas velocity generates strong airflow shear force, which effectively overcomes the surface tension of molten asphalt, prevents it from shrinking into island-shaped agglomerates, and forces the asphalt liquid film to spread evenly on the graphite surface.

[0030] After the heat preservation period, the process enters the extremely slow setting and curing stage: T2→T3, with a heating rate of 0.5-0.7℃ / min, a T3 temperature of 455±5℃, and an operating gas velocity of 0.8-1.0 times Umf. The rationale for these parameters is as follows: Extremely slow heating (0.5-0.7℃ / min): Entering the pre-pyrolysis temperature zone, the asphalt begins to undergo condensation reaction, with the molecular weight gradually increasing and viscosity rising. The extremely slow heating rate ensures that the asphalt liquid film has sufficient time to complete molecular rearrangement and pre-condensation, forming a uniform semi-solid set layer, avoiding film rupture or uneven shrinkage due to localized thermal stress. The final temperature of 455±5℃: At 455℃, the asphalt has essentially completed pre-condensation and setting, and the surface no longer has fluidity, providing a structurally stable precursor for the subsequent carbonization transition stage. Low gas velocity (0.8-1.0 Umf): Reducing the gas velocity during the setting process minimizes mechanical damage to the semi-solid coating layer caused by particle collisions, protecting the already formed uniform liquid film structure.

[0031] Carbonization transition section: T3→T4, after heat preservation, T4→T5, T4 is 550±5℃; T5 is 650±10℃; heating rate is 2-3℃ / min; operating gas velocity: 1.0-1.2 times Umf. Stepped heating (455→550→650℃): An intermediate heat preservation node is set at 550℃, so that the asphalt pyrolysis is completed in two steps—before 550℃, the main release is of small molecule light components, and from 550-650℃, the condensation of polycyclic aromatic hydrocarbons and the construction of the carbon layer skeleton are completed. Stepped pyrolysis avoids the concentrated escape of light components in a narrow temperature range, forming penetrating pores. Heating rate 2-3℃ / min: slightly faster than the setting section but still at a medium to low speed, taking into account both production efficiency and the control requirements of orderly release of volatiles. Final temperature 650±10℃: At 650℃, the asphalt pyrolysis is basically complete, and the carbon layer skeleton has been formed. However, the carbon layer still retains a certain amorphous structure, providing active sites for subsequent high-temperature graphitization pretreatment. Gas velocity 1.0-1.2 Umf: Stable fluidization state combined with slight negative pressure guides the volatiles to be discharged from the reactor in a timely manner, preventing them from undergoing secondary decomposition in the gas phase and forming carbon black contamination particles on the surface.

[0032] Carbonization treatment: After heating to 950±20℃ at a rate of 2-3℃ / min, hold the temperature; after that, continue heating to 1150-1200℃ at a rate of 1-2℃ / min. Holding at 950±20℃: This temperature range is the critical window for the transformation of amorphous carbon into a disordered graphite structure. Holding allows for the full release of internal stress in the carbon layer, gradually reducing the interlayer spacing. Final temperature of 1150-1200℃: Higher than the conventional final carbonization temperature (1000-1100℃), at this temperature the carbon layer further densifies while avoiding excessive graphitization that could lead to interfacial delamination between the carbon layer and the graphite substrate due to differences in thermal expansion coefficients. Heating at 1-2℃ / min: A slower heating rate is used in the final temperature range to ensure the gradual evolution of the carbon layer structure while avoiding microcracks caused by thermal shock.

[0033] The temperature-airflow field parameters for each stage are derived from asphalt thermogravimetric-differential thermal analysis and fluidized bed computational fluid dynamics simulation optimization, with clear control boundaries and strong robustness at each stage. Combined with laser interferometry in-situ monitoring (8nm resolution) closed-loop control, the consistency of coating thickness across different batches of products can be ensured, meeting the stringent requirements of battery materials for batch stability.

[0034] S6. Finished Product Integration and Refining: Surface-modified spheroidized graphite is sequentially subjected to low-frequency resonance mixing in the finished product section, final demagnetization, and finished product sieving to obtain spheroidized graphite composite materials.

[0035] Electromagnetic dry powder demagnetizing equipment with vibration dispersion function is used in pre-pickling demagnetization, post-pickling demagnetization, and final demagnetization stages. The core value of vibration dispersion is the key reason for selecting this equipment in this process. By applying high-frequency, low-amplitude vibration, it effectively breaks up any potential material agglomerations, ensuring that each graphite particle is exposed to the magnetic field, thus improving demagnetization quality. This equipment is a dry magnetic separation method, avoiding the introduction of moisture and eliminating the need for subsequent drying. It perfectly integrates with the entire process flow, reducing costs and demagnetization time. For example, using Guoming Equipment or Huatai Magnetoelectric's dedicated graphite demagnetizing equipment can effectively remove magnetic impurities.

[0036] Unlike existing technologies that simply pursue the limits of a single indicator or only make isolated process improvements, this invention provides a systematic solution for synergistic optimization of the entire process. Through the organic integration of three core technologies—multi-level precise shaping, deep gradient purification, and fluidized field reconstruction coating—the spherical graphite composite material prepared by this invention does not pursue the ultimate performance of a single property, but achieves excellent comprehensive balance and synergistic improvement in key dimensions such as specific capacity, initial efficiency, rate performance, cycle life, processing performance, and safety. Compared with products produced by existing technologies, this invention has the following beneficial effects:

[0037] 1. This invention employs a progressive multi-stage shaping strategy: pre-spheroidized flexible shaping + ultra-high-speed airflow pulverization for initial shaping + series airflow staged grinding for fine finishing + ultrasonic shaping. Compared to the shortcomings of existing technologies that rely on a single high-impact device, leading to excessive damage to the graphite lattice and an increase in microcracks, the segmented stirring rotor and gradient guide bushing design in step S1 of this invention effectively blunts the edges without breaking the graphite sheets through a progressive stress environment of dispersion-shearing-fine grinding. The multi-field coupled collaborative control model of airflow field-temperature field-particle field established in step S2 replaces the traditional method of relying on manual experience to adjust parameters, achieving precise control of particle collision energy and residence time. This technical solution significantly reduces subsurface damage and crystal defects inside graphite particles, protects the integrity of the graphite lattice, and achieves a half-cell specific capacity of 367 mAh / g, close to the theoretical upper limit of graphite capacity, far superior to the capacity loss caused by crystal structure damage in conventional processes (typically <360 mAh / g).

[0038] 2. This invention constructs a gradient impurity control system throughout the entire process. In the raw material pretreatment stage, a combination of sieving and negative pressure air classification is used to achieve physical impurity removal at the front end, utilizing the difference in hardness between graphite and impurities. Step S3 of this invention employs a step-by-step acid addition sequence based on the difference in impurity reaction kinetics (first adding hydrofluoric acid to attack silicates, then adding hydrochloric acid to dissolve metals, and finally adding nitric acid to form aqua regia for reinforcement), combined with intermediate washing with dilute hydrochloric acid to inhibit the hydrolysis and deposition of metal ions. Simultaneously, a three-stage electromagnetic demagnetization and low-frequency resonance mixing defense line is set up before acid washing, after acid washing, and before finished product processing. This refined purification logic significantly improves acid utilization efficiency, achieving the removal of stubborn silicates and trace metal impurities while reducing the amount of strong acids such as hydrofluoric acid. The product ash content is as low as 0.019%, and the total amount of magnetic foreign matter is only 0.02 ppm. The extremely low impurity content eliminates the potential micro-short circuit risk and electrolyte catalytic side reactions of LFP batteries from the source, further improving the intrinsic safety and low self-discharge characteristics of LFP batteries.

[0039] 3. Addressing the technical bottlenecks of existing asphalt coating technologies, such as the crude heating process leading to uneven coating thickness and the presence of penetrating pores, this invention proposes a fluidized field reconstruction coating technology. Step S5 innovatively designs a four-segment temperature-airflow field precise control model. Compared to the traditional mixing-one-step calcination process, the coating layer formed by fluidized field reconstruction in this invention is dense, continuous, and free of significant structural defects. This greatly enhances interfacial stability, effectively suppressing direct contact between the electrolyte and the graphite substrate during the initial charging process, improving the initial coulombic efficiency. Simultaneously, it significantly inhibits the continuous thickening of the SEI film and the consumption of active lithium during long-term cycling, achieving excellent cycle stability. The cycle stability of the negative electrode material in this invention is highly matched with the long-life characteristics of the LFP positive electrode, so that the cycle life of the entire battery is no longer limited by the negative electrode.

[0040] 4. The significant advantage of this invention lies in the synergistic effect between processes. The high sphericity shaping in steps S1-S2 provides regular and easily fluidized matrix particles for the fluidized field coating in step S5; the deep purification in step S3 removes surface polar impurities and metal catalytic sites, providing a clean adhesion interface for the carbon coating in step S5 and improving the adhesion of the coating layer; while the low-frequency resonant mixing and final refining in step S6 further ensure batch consistency. This end-to-end synergy results in a final product with an extremely narrow particle size distribution, high sphericity, and high tap density. In electrode processing, this material exhibits excellent processing tolerance: moderate slurry viscosity (1754 mPa·s), high peel strength (25.7 mN / mm), and an electrode rebound rate of only 4.0% after 24 hours at a compaction density of 1.65 g / cm³, with a maximum compaction density of 1.87 g / cm³ without particle breakage. These characteristics make it perfectly suited for high-speed coating and high-compaction-density electrode manufacturing processes.

[0041] In summary, this invention systematically solves the comprehensive challenges of existing spherical graphite anode materials in terms of specific capacity, first-cycle efficiency, cycle life, rate performance, safety, consistency, and cost through the synergistic process of three core technologies: multi-level precise shaping, deep gradient purification, and fluidized field reconstruction coating. It provides LFP batteries with a high-energy-density, long-cycle, high-safety, and batch-stable anode material solution. Detailed Implementation

[0042] The following are specific embodiments of the present invention, which further describe the technical solutions, but are not limited to these embodiments.

[0043] A method for preparing spherical graphite composite materials for LFP batteries specifically includes the following steps:

[0044] S1. Raw material pretreatment and pre-spheroidization: High-carbon flake graphite with a particle size of no more than 100 mesh and a carbon content of 95-96% is selected as raw material. Impurity removal and dispersion are carried out by screening and negative pressure air classification. Horizontal ultrafine grinding and online classification linkage control system are used for grinding to realize closed-loop linkage of grinding and classification and reduce over-grinding rate. Pre-spheroidization and flexible shaping are carried out by vertical stirred mill. The vertical stirred mill adopts segmented stirring rotor, which consists of dispersion section, shearing section and fine grinding section from top to bottom. The inner wall of the grinding chamber is equipped with matching gradient guide bushing to obtain pre-spheroidized graphite.

[0045] S2. Fine shaping: The pre-spheroidized graphite is sequentially shaped by ultra-high speed airflow pulverization, tandem airflow classifier milling, and ultrasonic shaping. The ultra-high speed airflow pulverization is controlled by a multi-field coupled PLC that controls the airflow field, temperature field, and particle field to regulate the airflow speed, inlet pressure, processing temperature, feed rate, and particle residence time. The tandem airflow classifier mill is equipped with a Sync real-time particle size monitoring device and a Venturi feeder to produce shaped spheroidized graphite.

[0046] S3. Deep purification: The shaped spherical graphite is subjected to demagnetization before acid washing, multi-stage acid washing, drying, low-frequency resonance mixing, and demagnetization after acid washing. The multi-stage acid washing is carried out by first adding hydrofluoric acid at 60±2℃, then adding concentrated hydrochloric acid at 65±2℃, and finally adding concentrated nitric acid at 70-75℃. After pressure filtration, it is washed with dilute hydrochloric acid and pure water in sequence to obtain intermediate purified material. Then, it is acid washed a second time with aqua regia at 70-80℃. After acid washing, it is washed with pure water with ultrasonic assistance to obtain purified spherical graphite.

[0047] S4. Particle size sieving: The purified spherical graphite is subjected to particle size sieving to control the sphericity ≥ 0.94, so as to obtain the spherical graphite to be coated.

[0048] S5. Fluidized Field Reconstruction Coating: High-soft-point petroleum-based asphalt with a soft point of 255-260℃, ash content <0.1%, coking value 60-65%, and quinoline insoluble matter 0.9-1% is used. After being pulverized to a D50 of 1-8μm, the asphalt is coated with spherical graphite at a mass ratio of 1:10. The coating is carried out in four stages within the fluidized bed:

[0049] 1) Rapid pre-layout section: room temperature → 300±5℃, heating rate 6-8℃ / min, gas velocity 1.1-1.3 times Umf;

[0050] 2) Slow melting and leveling section: 300±5℃→385±5℃, heating rate 1.5-2℃ / min, gas velocity 1.5-2.0 times Umf;

[0051] 3) Extremely slow setting and curing section: 385±5℃→455±5℃, heating rate 0.5-0.7℃ / min, gas velocity 0.8-1.0 times Umf;

[0052] 4) Stepped carbonization transition section: 455±5℃→550±5℃→650±10℃, heating rate 2-3℃ / min, gas velocity 1.0-1.2 times Umf;

[0053] After coating, the temperature is increased to 950±20℃ at 2-3℃ / min and held at that temperature, and then increased to 1150-1200℃ at 1-2℃ / min for carbonization to obtain surface-modified spheroidized graphite.

[0054] S6. Finished Product Integration and Refining: Surface-modified spheroidized graphite is sequentially subjected to low-frequency resonance mixing in the finished product section, final demagnetization, and finished product sieving to obtain spheroidized graphite composite materials for LFP batteries.

[0055] The parameter test report for spherical graphite composite materials is shown in Table 1.

[0056]

[0057] Table 1

[0058] Table 1 Data Analysis: Proper control of fine powder content means D10 indicates very few excessively fine particles. The benefits of less fine powder include: ① Reduced side reactions: Fine powder has a large specific surface area, making it prone to irreversible side reactions with the electrolyte, consuming active lithium; ② Improved initial efficiency: LFP batteries inherently have low energy density, making high initial efficiency of the negative electrode particularly important. A suitable D10 helps improve the initial coulombic efficiency; moderate and concentrated particle size is also beneficial.

[0059] The D50 median particle size is the ideal range commonly used for LFP anodes. Reasons: ① Good processing performance: The moderate particle size facilitates homogenization, coating, and rolling, and is less prone to scratches; ② Kinetic balance: It ensures sufficient lithium-ion diffusion channels without causing a decrease in rate performance due to excessively large particles; ③ Matching with LFP cathodes: Similar anode particle sizes help form a uniform electrode structure and reduce local current density differences.

[0060] A low D90 value indicates the absence of abnormally large particles. The hazards of large particles include: ① causing roughness and scratches on the coating surface; ② more dramatic volume expansion during charging, potentially leading to electrode cracking or puncture of the separator; ③ in LFP batteries, the negative electrode must withstand long-term cyclic stress, and coarse particles will accelerate electrode structure damage. This value indicates a narrow particle size distribution and good batch consistency.

[0061] Proper control of the maximum particle size is crucial for the safety of LFP batteries: ① Avoid large particles puncturing the separator (although LFP batteries have good thermal stability, mechanical puncture is still a risk); ② Avoid localized lithium plating; ③ Reduce particle breakage during rolling and improve electrode flatness.

[0062] A suitable specific surface area ensures sufficient lithium-ion insertion / extraction active sites (avoiding rate performance degradation) without being too high, which could lead to severe SEI film growth (otherwise, it would consume lithium resources, reducing initial efficiency and cycle life). LFP batteries have high cycle life requirements, and a moderate specific surface area helps maintain long-term cycle stability.

[0063] Extremely low ash content. The benefits of low ash content include: ① reducing the catalytic decomposition of the electrolyte by impurities; ② preventing impurities from becoming nuclei for side reactions, leading to uneven SEI film; and ③ improving the chemical stability of the material. LFP batteries are sensitive to impurities, and low ash content is fundamental to ensuring long lifespan and safety.

[0064] The extremely low magnetic impurity content (0.02 ppm) is a crucial indicator. Magnetic materials (Fe, Co, Ni, Cr, Zn, etc.) can dissolve and deposit during battery charging and discharging, leading to: ① Micro-short circuits: forming lithium dendrites or metal deposits, resulting in increased self-discharge or even thermal runaway; ② Catalytic side reactions: accelerating electrolyte decomposition and generating gas. Although LFP batteries themselves have good thermal stability, the introduction of magnetic foreign objects still poses safety hazards. 0.02 ppm is far below industry requirements, meaning the material can maximize the safety and low self-discharge rate of LFP batteries.

[0065] Overall Conclusion: The reasons why the data in Table 1 is suitable for LFP batteries are as follows: High purity: 0.019% ash content and 0.02ppm magnetic material ensure the intrinsic safety (no micro-short circuit risk) and ultra-long cycle life of LFP batteries (no impurity catalytic side reactions). Reasonable particle size distribution: no excessively fine powder or excessively large particles, matching the particle size of LFP cathodes, good processing performance, and suppressing lithium plating and electrode breakage. High tap density: directly improves volumetric energy density, compensating for the shortcoming of low energy density in LFP cathodes. Suitable specific surface area: balances rate performance and initial coulombic efficiency, which is beneficial for long-term cycle stability. In summary, the composite material of this invention achieves a level that highly matches the requirements of high safety, long life, and high consistency of LFP batteries in four dimensions: purity, particle size, specific surface area, and tap density.

[0066] The full performance test report of spherical graphite composite materials is shown in Table 2:

[0067]

[0068] Table 2

[0069] High specific capacity (367mAh / g): The half-cell capacity reaches 367mAh / g, close to the theoretical capacity of graphite. This is mainly attributed to the multi-stage precision shaping process in steps S1 and S2. Specifically, the pre-spheroidizing flexible shaping in step S1 employs a vertical stirred mill and a segmented stirring rotor, combined with a gradient flow guide bushing, to avoid single strong impacts causing fractures and microcracks in the graphite lattice. The ultra-high-speed airflow pulverization shaping in step S2, through multi-field coupled synergistic control (airflow field, temperature field, particle field), reduces crystal structure damage caused by excessive collisions and the incidence of over-refinement. These two processes together protect the integrity of the graphite crystals, enabling the material to achieve a specific capacity close to the theoretical value.

[0070] High initial coulombic efficiency: The initial efficiency is significantly higher than conventional levels, primarily due to the fluidized field reconstruction coating technology in step S5. This technology uses high-soft-point petroleum-based bitumen to construct a four-segment temperature-flow field within the fluidized bed. This precise segmented control allows the bitumen to form a dense, continuous, and non-porous coating layer on the graphite surface. During the initial charging process, this coating layer effectively prevents direct contact between the electrolyte and the graphite substrate, suppressing irreversible side reactions and excessive SEI film growth, thereby significantly reducing irreversible capacity loss and improving the initial coulombic efficiency.

[0071] Excellent rate performance: The excellent rate performance is attributed to the particle microstructure characteristics resulting from the combined effects of steps S1, S2, and S4. The pre-spheroidizing flexible shaping in step S1, combined with the ultra-high-speed airflow milling, tandem airflow classifying milling, and ultrasonic shaping in step S2, imparts high sphericity (finished product sphericity ≥ 0.94) and a narrow particle size distribution to the graphite particles. Particle size sieving in step S4 further ensures particle size concentration. High sphericity and narrow distribution facilitate rapid diffusion of lithium ions within the particles, reducing concentration polarization; simultaneously, the specific surface area is within an ideal range, providing sufficient reaction interfaces while avoiding excessive interfacial side reactions. These optimized microstructures collectively support the material's capacity retention under high-current charge and discharge conditions.

[0072] Cyclic stability is one of the most prominent advantages of this invention, mainly stemming from the fluidized field reconstruction coating in step S5 and the deep purification in step S3. On one hand, the extremely slow solidification stage and step-by-step carbonization transition in S5 form a structurally stable coating layer that is firmly bonded to the graphite matrix. This coating layer can continuously block electrolyte penetration during long-term cycling, inhibiting the continuous thickening of the SEI film and the irreversible consumption of active lithium. On the other hand, step S3, through stepwise acid-mixed acid washing, aqua regia-enhanced washing, and three stages of electromagnetic dry powder demagnetization before, after, and before the finished product, reduces the magnetic impurity content to 0.02 ppm and the ash content to only 0.019%. This extremely low impurity content avoids the catalytic decomposition of the electrolyte by metallic foreign matter or the initiation of micro-short circuits, thereby eliminating the accelerated capacity decay caused by side reactions, far superior to conventional products.

[0073] Lower internal resistance helps reduce battery polarization and heat generation, mainly due to the deep purification process in step S3 and the high-temperature carbonization treatment in step S5. The deep purification process removes non-conductive impurities from the surface and interior of the graphite particles, reducing contact resistance and interfacial charge transfer impedance. The carbonization treatment in step S5, with a final temperature of 1150-1200℃, higher than the conventional carbonization final temperature (1000-1100℃), further densifies the carbon coating and increases its graphitization, thereby enhancing the electronic conductivity of the coating. This is beneficial for high-current charging and discharging and thermal management.

[0074] Excellent processing performance (viscosity, compaction, peeling, rebound rate): This is mainly attributed to steps S1 and S2. The multi-stage shaping process endows the graphite particles with high sphericity and high tap density, which ensures uniform particle dispersion in the slurry and good slurry rheological properties. During rolling, the particles are densely stacked and the stress distribution is uniform, thus achieving high compaction density and low rebound. The low-frequency resonant mixing in the finished product section of step S6 achieves powder homogenization without secondary particle breakage, further ensuring batch-to-batch consistency, which is beneficial to the stability of coating and rolling processes and improves the electrode manufacturing yield.

[0075] In summary, each of the superior properties listed in Table 2 is not an isolated phenomenon, but rather the result of synergistic optimization across the entire process from raw material pretreatment to finished product refining. High capacity stems from the shaping process that protects crystal integrity; high initial efficiency and long cycle life rely on the dense carbon layer formed by fluidized field reconstruction coating technology; excellent rate capability benefits from high sphericity and narrow particle size distribution; low internal resistance and high purity depend on deep gradient purification and multi-stage demagnetization; and good processability comes from particle morphology control and low-frequency resonant mixing. These process steps work together to ensure that the spherical graphite composite material fully meets the stringent requirements of LFP batteries for high energy density, long lifespan, high safety, and high consistency.

[0076] The greatest advantage of this invention lies in its comprehensiveness: it is not a single-item champion, but an all-around anode material with balanced performance across all aspects and no significant weaknesses. This comprehensive performance advantage allows it to perfectly match the multiple requirements of LFP batteries for high safety, long life, high energy density, and high consistency, and it has broad application prospects in the fields of power batteries and 3C products.

[0077] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or substitute them with similar methods, without departing from the spirit of the invention or exceeding its defined scope. Although the invention has been described in detail above, such descriptions are considered illustrative or exemplary rather than restrictive. It should be understood that changes and modifications can be made by those skilled in the art within the scope of the following claims.

Claims

1. A method for preparing spherical graphite composite materials for LFP batteries, characterized in that, Specifically, the following steps are included: S1. Raw material pretreatment and pre-spheroidization: High-carbon flake graphite raw materials are subjected to impurity removal, dispersion, crushing, and pre-spheroidization flexible shaping treatment to obtain pre-spheroidized graphite; requirements for high-carbon flake graphite raw materials: particle size not greater than 100 mesh, carbon content 95-96%; In the pulverization process, a pulverization system with horizontal ultrafine pulverization and online classification linkage control is adopted to realize closed-loop linkage control of pulverization and classification, thereby reducing the over-pulverization rate while controlling the particle size. In the pre-spheroidizing flexible shaping process, a grinding system with vertical stirred mill and online classification linkage control is adopted. In the vertical stirred mill, a segmented stirring rotor and a spiral curved stirring arm are used to avoid the increase in graphite fracture rate caused by a single strong impact. The segmented stirring rotor is divided into a dispersion section, a shearing section and a fine grinding section from top to bottom, with the diameter increasing segment by segment. The inner wall of the grinding chamber is equipped with a gradient flow guide bushing that matches the segmented stirring rotor to reduce the deposition of materials in corners and segregation caused by particle size differences. S2. Fine shaping: The pre-spheroidized graphite is subjected to ultra-high speed airflow pulverization shaping, series airflow staged milling shaping and ultrasonic shaping in sequence to obtain shaped spheroidized graphite; In the ultra-high-speed airflow pulverization and shaping process, an ultra-high-speed airflow pulverization and shaping machine is used. By establishing a multi-field coupled collaborative control model of airflow field, temperature field, and particle field, linkage control is carried out. While completing rapid preliminary spheroidization shaping, the occurrence rate of crystal structure damage or over-refinement caused by excessive collision is reduced. S3. Deep purification: The shaped spherical graphite is subjected to demagnetization before acid washing, multi-stage acid washing, drying, low-frequency resonance mixing of graphite, and demagnetization after acid washing in sequence to obtain purified spherical graphite. The multi-stage pickling process includes stepwise acid addition mixed acid pickling, pressure filtration and intermediate washing, and aqua regia pickling. In the stepwise acid addition mixed acid pickling, water and shaped spheroidized graphite are added sequentially to the first-stage pickling container, followed by the sequential addition of hydrofluoric acid solution, concentrated hydrochloric acid, and concentrated nitric acid to improve acid utilization. In the pressure filtration and intermediate washing, dilute hydrochloric acid and water are used sequentially for cleaning to obtain intermediate cleaning material. In the aqua regia pickling, water and intermediate cleaning material are added sequentially to the second-stage pickling container, followed by the addition of aqua regia formed by the mixture of concentrated hydrochloric acid and concentrated nitric acid. S4. Particle size sieving: The purified spherical graphite is subjected to particle size sieving to obtain spherical graphite that meets the requirements for coating. S5. Fluidized Field Reconstruction Coating: Using pulverized high-soft-point petroleum-based asphalt as raw material, fluidized field reconstruction technology is employed. By constructing multiple temperature-gas flow fields and controlling the heating rate, temperature nodes, and fluidizing gas velocity at each stage, the spherical graphite to be coated is coated. After coating, a stepped heating method is used for carbonization treatment to obtain surface-modified spherical graphite. The coating treatment includes four stages: a rapid pre-spreading stage, a slow melting and leveling stage, an extremely slow shaping and solidification stage, and a stepped heating carbonization transition stage. S6. Finished Product Integration and Refining: Surface-modified spheroidized graphite is sequentially subjected to low-frequency resonance mixing in the finished product section, final demagnetization, and finished product sieving to obtain spheroidized graphite composite materials.

2. The method for preparing spherical graphite composite materials for LFP batteries as described in claim 1, characterized in that, In the impurity removal and dispersion process in step S1, a combination of screening and negative pressure air separation is adopted; in screening, a screen with an integrated high-frequency micro-vibrator is used; in negative pressure air separation, a negative pressure air separator equipped with a dispersing device at the feed inlet is used.

3. The method for preparing spherical graphite composite materials for LFP batteries as described in claim 1, characterized in that, In step S1, the horizontal ultrafine pulverizer and the online classification linkage control pulverization system include a pulverizing device, the inlet of which is connected to a vibrating frequency conversion feeding device with a buffer bin; the outlet of the pulverizing device is connected to the inlet of the classification device, and a dispersing device is provided between the outlet of the pulverizing device and the inlet of the classification device; an anti-static device is provided at the inlet of the classification device; a particle size analyzer is provided in the classification device; the fine powder outlet of the classification device is connected to a cyclone collector, and the coarse powder outlet of the classification device is connected to the return port of the pulverizing device through a sealed return pipe; The crushing device, grading device, and vibration frequency conversion feeding device are all electrically connected to the control device. The control device is used to receive the particle size signal fed back in real time by the particle size analyzer, and to adjust the grading speed parameters of the grading device, the crushing parameters of the crushing device, and / or the feeding parameters of the frequency conversion feeding device in linkage according to the preset particle size range.

4. The method for preparing spherical graphite composite materials for LFP batteries as described in claim 1, characterized in that, The gradient guide bushing is configured as follows: Upper guide dispersion section: shallow spiral guide grooves are opened on the inner wall, and the groove shape is a circular arc groove; Middle gradient shear section: bidirectional cross spiral grooves are opened on the inner wall, with positive and negative spiral grooves distributed alternately to form a cross turbulent flow trajectory; Lower strong grinding and stabilizing section: dense toothed axial stabilizing grooves are opened on the inner wall, with the groove shape being an axial straight groove + bottom circular arc transition, and the bottom of the groove and the groove surface forming a step difference to enhance the rolling and friction effect of the medium.

5. The method for preparing spherical graphite composite materials for LFP batteries as described in claim 1, characterized in that, In step S2, the process of establishing the multi-field coupled collaborative control model is as follows: by defining the devices associated with each field, collecting the characteristic parameters of each field under multiple operating conditions, establishing a global database, constructing the collaborative control logic between the parameters of each field, embedding the PLC control device, and verifying and optimizing it through trial operation, the linkage control of the airflow field, temperature field, and particle field is realized. The parameters involved in the establishment process include: airflow field parameters, temperature field parameters, and particle field parameters; among which, the airflow field parameters include airflow velocity, inlet pressure, and airflow rate; the temperature field parameters include the working temperature of the processing chamber and the temperature adjustment accuracy; and the particle field parameters include feed parameters, particle concentration, particle residence time, and particle size detection parameters.

6. The method for preparing spherical graphite composite material for LFP batteries as described in claim 1, characterized in that, In the series airflow classifying mill shaping process in step S2, a Sync real-time particle size monitoring device is configured using laser diffraction combined with AI algorithm to provide timely feedback and adjust the classification parameters in order to control batch differences. A Venturi feeder is used. The Venturi feeder has a specific contraction angle design in the contraction section to ensure smooth airflow acceleration, and the feeding structure is arranged in an inclined manner to optimize material introduction. Several auxiliary airflow introduction structures are set in the expansion section.

7. The method for preparing spherical graphite composite materials for LFP batteries as described in claim 1, characterized in that, Electromagnetic dry powder demagnetizing equipment with vibration dispersion function is used in pre-pickling demagnetization, post-pickling demagnetization, and final demagnetization.

8. The method for preparing spherical graphite composite material for LFP batteries as described in claim 1, characterized in that, In step S3, the specific process of multi-stage acid washing is as follows: Stepwise acid addition mixed acid washing: Water and shaped spheroidized graphite are added to the first-stage acid washing container in sequence, and acid solutions are added in the following order: First, hydrofluoric acid solution is added and reacted at 60±2℃ for a certain period of time; then concentrated hydrochloric acid is added and reacted in an acidic environment where hydrofluoric acid and hydrochloric acid coexist for a certain period of time at a reaction temperature of 65±2℃; finally, concentrated nitric acid is added and reacted in an acidic environment where hydrofluoric acid, hydrochloric acid, and nitric acid coexist for a certain period of time at a reaction temperature of 70-75℃. The first stage pickling material was obtained; Filtration and intermediate washing: After the first-stage acid washing material is pressure filtered, it is washed with dilute hydrochloric acid solution and water in sequence to obtain intermediate purified material; Aqua regia acid washing: Water and intermediate purified material are added to the second-stage acid washing container in sequence, and then aqua regia solution is added for acid washing. The acid washing temperature is 70-80℃; After acid washing, pure water ultrasonic-assisted washing is used for washing.

9. The method for preparing spherical graphite composite material for LFP batteries as described in claim 1, characterized in that, In step S5, the parameters for high-soft-point petroleum-based asphalt are: soft point 255-260℃, ash content <0.1%; coking value 60-65%. The quinoline insoluble content is 0.9-1%; the weight ratio of high-soft-point petroleum-based asphalt to spherical graphite to be coated is 0.8-1:

10. Multi-segment temperature-airflow field: First, the system enters the rapid pre-spreading section: the temperature is increased from room temperature to T1 at a rate of 6-8℃ / min, T1 is 300±5℃, and the operating gas velocity is 1.1-1.3 times Umf; after holding at this temperature, the system enters the slow melt-leveling section: the temperature is increased from T1 to T2 at a rate of 1.5-2℃ / min, T2 is 385±5℃, and the operating gas velocity is 1.5-2.0 times Umf; after holding at this temperature, the system enters the extremely slow... Curing and setting section: The temperature is increased from T2 to T3 at a rate of 0.5-0.7℃ / min, with a T3 temperature of 455±5℃ and an operating gas velocity of 0.8-1.0 times Umf. After the holding period, the temperature is increased to T4. After the holding period, the temperature is increased from T4 to T5, with a T4 temperature of 550±5℃ and a T5 temperature of 650±10℃. The heating rate is 2-3℃ / min, and the operating gas velocity is 1.0-1.2 times Umf. Carbonization treatment: After heating to 950±20℃ at a heating rate of 2-3℃ / min, hold the temperature; after the end, continue heating to 1150-1200℃ at a heating rate of 1-2℃ / min.

10. The method for preparing spherical graphite composite material for LFP batteries as described in claim 1, characterized in that, The parameters for spherical graphite composite materials are as follows: Particle size: D10≥8.0um; D50 is 16±2um; D90≤32um; Dmax≤45um; Tap density≥1.10g / ml; Ash content≤0.05%; Moisture content≤0.1%; Fe+Co+Ni+Cr+Zn content≤1ppm.

Images